GREEN BANK 3 - National Radio Astronomy ObservatoryVLBI Global Network Call for Proposals Correlator...

ATACAMA LARGE MILLIMETER ARRAY (ALMA)

GREEN BANK

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IN GENERAL

NEW RESULTS

ALMA Project Progress Report

The Green Bank TelescopeLatest Results from the GBT Precision Telescope

Control System ProjectThe Green Bank Telescope Joins 7-mm VLBI CommunityGBT Student Support Program:

Announcement of Awards

VLA Configuration Schedule; VLA/VLBA ProposalsVLBI Global Network Call for ProposalsCorrelator Station PositionsVLA/VLBA Observing for University Classes or

Summer ProgramsThe Status of the NRAO Data ArchiveVLA and VLBA Large Proposal Results

New VLSS Data Release Now AvailableGreen Bank Conference on the Discovery of Sag A*From the Spectrum ManagerColor Figures in Proposals2004 Summer Student ClassA Change in Editor for the Newsletter

Detection of the Intrinsic Size of the Galactic-CenterBlack Hole Radio Source, Sagittarius A*

Comparing Dust and Gas in Interstellar Space

Detailed Radio Images Seen Through aGravitational Lens

Resolving the Afterglow of a Gamma-ray Burst

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TABLE OF CONTENTS

Cover Image: The Very Long Baseline Array (VLBA) is the world's largest, full-time astronomical instrument, consisting of a series of 10 radioantennas spread out across North America from Hawaii to the Virgin Islands. Each antenna is 82 feet (25 meters) in diameter, weighs240 tons, and is nearly as tall as a ten story building. The antennas, controlled by the Array Operations Center in Socorro, New Mexico,function together as one instrument with very high resolution and sensitivity. The data from each antenna is recorded onto magnetic tapesand sent by mail to the astronomers doing the observations. The VLBAwas dedicated in 1993 and is used by astronomers around the world.

The NRAO Graphics Department will be happy to assist you in the production of images for your article as well as for

your research papers. Contact Patricia Smiley ( ) with your request.

If you have an interesting new result obtained using NRAO telescopes that could be featured in this section of the NRAO

Newsletter, please contact Mark Adams at . We particularly encourage Ph.D. students to describe their

thesis work.

Editor: Barry Turner ( ); Assistant Editor: Sheila Marks; Layout and Design: Patricia Smiley

[email protected]

[email protected]

[email protected]

Cover image courtesy of: NASA/GSFC and ORBIMAGE, NRAO/AUI

July 2004 ALMA Issue 100

ATACAMA LARGE MILLIMETER ARRAY (ALMA)

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ALMA Project Progress Report

Two of the three unfilled key positions in the JointALMA Observatory (JAO) offices have been filled.

Tony Beasley has accepted AUI/NRAO’s offer tobecome ALMA Project Manager in the JAO. It isanticipated that he will begin serving in this position inSeptember in Chile. Prior to this, he will be participatingin ALMA meetings, the first of which was the ALMAScience Workshop held in May at the University ofMaryland. Tony has been Project Manager forCARMA at Caltech; before taking that position he heldthe Assistant Directorship for Program Development inCharlottesville, and before that, the Deputy AssistantDirectorship for VLA/VLBA computing.

Rick Murowinski has accepted AUI/NRAO’s offer tobecome ALMA Project Engineer in the JAO. He beganhis duties on May 18, 2004. Rick comes to ALMAfrom The Astronomy Technology Research Group(Victoria), where he has been Deputy Leader ofthe group and working on ground- and space-basedinstrumentation for large telescopes, Gemini and JWSTamong others. Rick’s research interests are in solidstate detector physics. The move to ALMA brings hiscareer in a full circle from its start at Algonquin RadioTelescope and then working on SIS mixers at Chalmer's

Institute of Technology (Goteberg). Rick will take upduties for JAO while initially remaining based inVictoria. Once the new Chilean offices are ready thisfall, he'll move to Santiago.

The project continues to search for a candidate to fillthe position of Project Scientist, to be in charge ofcommissioning and science verification of ALMA.

The interface between the Executives and the JAO hasbeen clarified by a Management Plan defining imple-mentation of the management structure outlined in theBilateral Agreement. Project management has beendeveloping a Project Management Control System(PMCS) to define an integrated project schedule and totrack costs and performance. The PMCS will beimplemented over the course of the remainder of theyear.

At the end of May, testing of the prototype antennas atthe ALMA Test Facility on the VLA site concluded.Radiometric tests of the Alcatel/EIE antenna concludedthe suite of tests; a report on the performance of thatantenna and the Vertex/RSI antenna was delivered tothe project by the Antenna Evaluation Group. Even asthe final tests were occurring on the prototype antenna,a joint technical evaluation group was evaluating bidsfor construction of the production antennas. The report

This picture is of the ALMA camp - the living quarters are on the far right. Dining and office space are behind that. The first project employ-ees moved in on June 1, 2004. On the far left in the distance is the contractor camp. This picture is taken from above the camp, looking overthe salt lake to the north end of which San Pedro is located. Photo by Jim and Debra Shepherd.

July 2004 ALMA Issue 100

of this group will be delivered to the project in June,followed by evaluation of the commercial portion ofthe bid. It is expected that a contract for the productionantennas will be let in September.

Visitors to the ALMA Camp (see photo on previouspage) at the site of the Operations Support Facility(OSF) will find several temporary offices and sleepingfacilities now, along with a splendid outdoor grill areaas ALMA staff take up residency. The road from theOSF to the Array Operations Site (AOS) is in anadvanced stage of completion. A request for bids forthe initial phase of construction of the AOS TechnicalBuilding has been issued; excavation is expected tocommence in the fall. Office space for ALMA inSantiago has been secured and will be ready for occu-pancy this fall.

The first of several moves from Arizona occurred inJune with the arrival of the Tucson Receiver Group inCharlottesville. During the next several months anALMA Integration Center will take shape in the NRAOTechnology Center in preparation for the production ofthe major ALMA systems.

Since mid-March, all ALMA receiver cartridges haveundergone preliminary design reviews; no substantialproblems were found. Assembly of the first completeALMA Front End, comprising all four cartridges in thedewar, is scheduled to begin in January 2005. A majorimprovement to the baseline correlator design is a tun-able filter bank card, replacing the original single filtercard. This increases the correlator flexibility , notably theresolution in the widest bandwidth is increased by a fac-tor of 32. Details of the plan to implement this improvedfilter bank are in their final stages. Integration of the ele-ments of the ALMA system has begun, providing thefirst opportunity to perform tests of substantial portionsof ALMA hardware and software. Following lab integra-tion, the prototype hardware will be installed at the ATFfor testing on the prototype antennas.

An ALMA Operations Plan has been drafted to providea view of the future operations phase of ALMA. TheChair of the Operations Planning Group has beenDarrel Emerson, working with his counterpart at ESODavid Silva, and representatives of all ALMA teams.

The Operations Plan is reaching maturity, with detailsof budget and personnel and deployment of those per-sonnel included in the upcoming version. One elementof the Plan is the local ALMA center, the ALMARegional Center (ARC). In North America, the ARCwill be embedded in a more fully functional center, theNorth American ALMA Science Center (NAASC).While the ARC provides the bare essentials — proposalhandling, observing file generation and distribution ofdata to the user — the NAASC adds to these the levelof support services users find at other NRAO facilities.

Paul Vanden Bout was appointed the first Head of theNAASC and will participate in more fully defining thefacility during the coming months. During May, anALMA Science Workshop was held at the Universityof Maryland to familiarize future users with use of theinstrument, and to provide definition for the interactionbetween ALMA and its users centered in the NAASC.This is the first of a series of workshops designed tofamiliarize future users with ALMA.

At the workshop, astronomers discussed their scientificexpectations from ALMA, led by overviews fromA. Blain (Caltech), N. Evans (Univ. of TX.), M. Meixner(STScI) and M. Gurwell (CfA). Blain noted that thehigh resolution available from ALMA enables itsimages to avoid confusion from overlapping sourcesand resolve their internal structure; ALMA providesin less than an hour spatially and spectroscopicallyresolved images of the most interesting galaxies found.Evans described ALMA’s contributions to starformation studies, from the revelation of the detailedstructure of star-forming clouds in other galaxies to theuse of absorption against circumstellar disks to revealmotions leading to star formation on fine scales.Meixner noted that ALMA’s high resolution andsensitivity in the submillimeter range would lead todetection of photospheric emission from a host of nor-mal stars, and detail the complex spatio-kinematicstructure of the envelopes of evolved stars. Gurwellhighlighted ALMA’s high imaging dynamic range,enabling it to image planetary phenomena as diverseas volcanic plume evolution on Io, vertical thermalstructure and winds in the atmospheres of Mars andVenus, or the gas streaming from disintegrating

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July 2004 ALMA and Green Bank ssue 100

cometary nuclei to inform our knowledge of primoridalsolar system chemistry. During breakout sessions, thefocus turned to specific examples of ALMA projects asdescribed in the Design Reference Science Plan (seewww.alma.nrao.edu/science). Returning to the plenarysession, representatives of North American radiofacilities described their instrumental plans for theALMA era. Discussion of support needed to extract

the best science from the huge ALMA data output (upto 5 TB/day of data) extended late into the night. Thenext day, summaries were presented as the workshopclosed. Members of the ALMA North AmericanScience Advisory Committee (see http://www.cv.nrao.edu/naasc/admin.shtml) held a face-to-face meeting tosynthesize the results of the workshop for inclusion ina written report.

H. A. Wootten

The Green Bank Telescope

The first half of 2004 has seen a significant number ofhigh quality scientific results from the GBT. Since thebeginning of the year, a substantial number of papershave been submitted, including about nine ApJ Letterspublished or in press. Highlights include papers on thebinary double pulsar, high velocity clouds about M31,studies of the fine structure constant, detections of highredshift molecular lines, and detections of new inter-stellar molecules. Nearly all of the major observingcapabilities are working completely and reliably, andobservers are clearly utilizing them to good effect.

From January through April of this year, ~62 percentof total telescope time (on a 24-hour-day basis) wasscheduled for science. Fractions will be somewhatlower during the summer months while structuralinspections, painting, and other engineering activitiesare underway, but will rise again in the fall. From mid-September through mid-May, the GBT is dynamicallyscheduled to match projects with weather requirements.

With the increase in observing time and available capa-bilities, the backlog of proposals from previous calls isbeing steadily reduced. The low frequency (<10 GHz)backlog is now effectively eliminated. Nearly 1000 hoursof approved time still remains in the queue for higherfrequencies, but should be eliminated this coming falland winter. At the recent June 1, 2004 deadline (forTrimester 04C), 700 hours of low frequency and

200 hours of high frequency time were requested.These numbers should increase again at the October call.

This summer our inspection contractor, Modjeski &Masters, is undertaking the second installment of GBTstructural inspections begun last summer. Last summer,critical members in the tipping structure were inspected;this summer half the reflector backup structure and all

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The Robert C. Byrd Green Bank Telescope at night.

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July 2004 Green Bank Issue 100

the alidade structure will be inspected. No inspectionsare scheduled for 2005, although inspections areplanned on a periodic basis for future years. Structuralpainting will also resume this summer, and will be anannual activity for several years. As reported inprevious newsletters, some defects were found lastsummer in the elevation shaft assembly welds.Following extensive investigation and inspection, thesedefects were determined to be shrinkage cracks fromthe original welding and do not appear to be the resultof fatigue. Several of these defects were ground outand rewelded, and others will be monitored for anychanges. Provided that no significant changes in theshaft weldments are noted, this does not appear to be aserious problem.

The NRAO staff and our engineering consultant,SG&H, continue to study the behavior of the azimuthtrack and to develop plans for long-term repairs ormodifications. Finite element models have been suc-cessful in describing the dynamical properties of thewear plate and base plate assembly, and accounting forthe probable fretting wear mechanism. The mechanismfor wear plate fatigue is still under study. In themeantime, the maintenance staff has found effectivemeans to manage the problems, albeit with effort andexpense. Little or no observing time is presently beinglost to the track. It is unlikely that major modificationwork will be scheduled to occur before 2006 unless thepresent performance or behavior of the track shouldchange.

The NRAO staff and our university collaborators continueto make good progress on GBT development projects.The new 26-40 GHz (Ka-band) pseudo-correlationreceiver was completed in April and has undergonefirst engineering evaluations on the telescope. Only alimited set of test observations has been undertaken,but performance looks good. This receiver willundergo full astronomical commissioning in the falland early winter when high transparency weatherreturns. The Caltech Continuum Backend, a fastswitching, large bandwidth backend designed for usewith the 26-40 GHz receiver, underwent a recentproject review and appears on track for delivery thisfall. Work on this project is being shared by Caltech

and the NRAO. The Penn Array camera project, acollaborative effort of UPenn, NASA-Goddard, NIST,U. Cardiff, and NRAO to construct a 64-pixel, 3 mmbolometer array for the GBT is also progressing well.The full cryogenics system is assembled and functioningwell and the optics tower has been installed recently.Delivery of the Penn Camera is expected in 2005. ThePrecision Telescope Control System project to deliver3 mm telescope capability for the GBT is progressingvery well and is described in a companion article. Thesoftware group has recently delivered a number ofcapabilities to observers including a single dish FITS(SDFITS) data export format, binary data files for theCLASS data reduction system, and progress toward anIDL data reduction capability. Finally, work toward anew configuration and observing interface to the GBTis proceeding very well, and is scheduled for betarelease in mid-summer.

P. R. Jewell

Latest Results from the GBT PrecisionTelescope Control System Project

The goal of the GBT Precision Telescope ControlSystem (PTCS) project is to allow the GBT to workeffectively at frequencies up to 115 GHz (wavelengthsdown to 3 mm). It is now just a little over a year sinceour Conceptual Design Review, and we have alreadymade excellent progress, culminating in the delivery ofusable Q-band (43 GHz, 7 mm) performance in thespring of this year. After an initial period of instrumen-tation development during summer 2003, during thefall we developed and released significantly improvedstrategies for pointing and focus corrections. Morerecently, we have started the detailed characterizationof the antenna efficiency and surface accuracy. Each ofthese activities is briefly described below.

Pointing/Focus

It was well known from the original GBT design studiesthat thermal gradients in the antenna would be one ofthe largest so-called “non-repeatable” sources of point-ing and focus error. Thermal gradients may introduceup to ~30 arcseconds of pointing error under the most

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extreme conditions. This affects theblind pointing both directly, and alsoindirectly, by introducing systematicerrors into traditional (gravity only)pointing models developed using con-ventional techniques. Changes in thethermal gradients may introduce driftsin offset pointing over the requiredtracking timescales of one-half to onehour. Finally, thermal gradients maycause tens of millimeters of radialfocus error, an effect not explicitlyanticipated during early GBT opera-tion. All of these effects meant that inthe spring of 2003, although the GBTwas capable of 26 GHz operation,observations required frequent offsetpointing and focus checks.

The performance of the antenna hasnow been substantially improved, to thelevel required for Q-band operation, by the develop-ment of an elegant but operationally simple mechanismfor correcting in real time for the effects of thermalgradients in the antenna. During the summer of 2003,we installed a system of ~20 precision temperaturesensors on the antenna subreflector, feedarm,primary backup structure and alidade. These have anabsolute accuracy of 0.15 deg C, and are read out overRS232/Ethernet at a 1 Hz rate. During the fall, weperformed a number of pointing runs, where azimuth,elevation and radial focus offsets were measured astro-nomically, while temperature data was simultaneouslylogged. Through physical intuition, insight and discoveryvia numerical experimentation, we chose a series of“features,” or linear combinations of temperaturesensors, to characterize deformations of the substruc-tures of the GBT. For example, the difference betweenthe subreflector and mean temperature of the primarybackup structure represents the difference in materialthermal expansion coefficient between the primary(steel) and subreflector (aluminum). We then performedlinear regressions between these features and theastronomically measured data. These regressionssimultaneously estimate the feature coefficients and thetraditional gravity pointing terms, so that we end up

with both a thermally-neutral gravity model, and thethermal corrections to the gravity model. The modelswere then tested by applying them to additional, inde-pendent datasets. An example for focus is shown inFigure 1. This shows the results of repeated focusmeasurements on a source, 0117+8928, within onedegree of the north celestial pole, and hence effectivelystationary in azimuth and elevation. All of the focusvariations are therefore due to thermal gradients. Thedata span a 24 hour period, with some daytime meas-urements rejected due to high wind. The measured dataare shown as black crosses, while the predictions of themodel are the red dots. As can be seen, the model doesan excellent job of removing the large (~30 mm) diurnalvariation in focus. Similar results are obtained forazimuth and elevation pointing error.

This scheme has now been implemented within the GBTmonitor and control system, with the model being eval-uated in real-time, and corrections to pointing and focusapplied automatically every 10 seconds. Using thiscorrection system, we routinely achieve 68th percentilefocus residuals of < 3 mm, and pointing residuals of~3" or better in each axis under benign conditions. Themodel is now being extended to account for other

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Figure 1. A test of the focus thermal model. Black crosses are the measuredpositions, red dots the prediction of the model. X-axis is local time in hours,Y-axis focus offset in mm.

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Surface Measurements

In line with our intermediate priorities to deliver Q-bandoperation for this past winter, the bulk of the PTCSefforts to date have been devoted to pointing improve-ments. However, we have also made some surfaceaccuracy and efficiency measurements. We have usedtwo independent methods to measure surface deforma-tions. First, we have used traditional phase-coherentholography, performed at 12 GHz using a geo-stationarysatellite at an elevation angle of about 42 degrees, nearthe rigging angle. Secondly, we have used the phase-retrieval technique (also known as the “out-of-focus”beam map, or OOF technique) developed andimplemented by the Radio Astronomy Group at theUniversity of Cambridge, UK. In this approach, onlythe power pattern of the antenna is measured, usuallyat two or more different focus settings. The phase ofthe signal in the aperture is later recovered bynumerical processing. Usually, this technique is used

with artificial sources, but the Cambridge grouphave extended this to provide measurement ofsurface errors with moderate spatial resolution,by observing astronomical sources usingexisting astronomical receivers. We have testedthis technique at 12, 22, and 43GHz, usingastronomical methanol, water, and SiO masersources. The two techniques are complementary:phase-coherent holography provides higherresolution, but our system is currently restrict-ed to 12 GHz and a single elevation; the OOFtechnique provides lower spatial resolution, butcan be performed over a range of elevations,and at higher frequencies.

The results of a 150× 150 point phase-coherentholography map (~0.7 m resolution on the dish)is shown in Figure 2. The correspondingOOF maps show good agreement. Details atthe individual panel level (especially a fewstuck actuators) are easily visible in the holog-raphy amplitude and phase plots. However, therms surface error in these maps, ~ 400 microns,is entirely dominated by the large-scale error,which is well represented by a series ofZernike polynomials.

We have measured a 43 GHz gain-elevation curve forthe GBT, without any attempt to correct for residualthermal or gravitational distortions. The efficiencypeaks at around 0.43 at 52 degrees elevation, and fallsoff symmetrically at higher and lower elevations. Theabsolute efficiency scale is somewhat uncertain due touncertainties in the receiver calibration. However, themeasured value of 0.43 gives a Ruze equivalent surfaceerror of 390 microns, in good agreement with theholography measurements.

Since measuring this gain-elevation curve, we haveperformed tests of the surface corrections predicted bythe holography measurements, by performing back-to-back measurements on 3C286 and 3C279, with andwithout the corrections applied. Unfortunately,attempts to determine absolute efficiencies using thesemeasurements were prevented by the uncertainties inthe receiver calibration, and the poor weather conditions

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Figure 2. A false-color image of a phase-coherent 12 GHz holog-raphy map showing the total wavefront error. The peak to peakrange is −1.3mm (blue) to +1.3mm (yellow); the rms error is~400 microns. 1.3mm, the rms error ~400 microns.

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at the time of the observations. However, in all cases,the peak gain was improved (by ~20-30 percent), thebeam FWHM became closer to the theoretical value,and sidelobes were significantly reduced. We aretherefore confident that we can use holographic meas-urements to substantially improve the surface accuracyof the antenna.

Future Work

The PTCS project has fallen naturally into a six-monthcycle, with instrumentation development work pro-ceeding primarily in the summer, and extensive com-missioning work performed mainly during the winterhigh-frequency observing season. We are currentlyupgrading the temperature sensors, and installing incli-nometers and accelerometers. We are planning a seriesof experiments using infrared thermography of the pri-mary surface in conjunction with OOF beam maps toattempt to isolate (and correct for) thermal gradient fig-ure error, and simultaneously refine the FEM model ofgravitational distortions, much the same as was done inour pointing corrections. Our goal is to deliver proto-

type 86 GHz operation in the Spring of 2005, with full115 GHz operation to be delivered a year later.

Further details of the PTCS project are available at:http://wiki.gb.nrao.edu/bin/view/PTCS/WebHome.

Acknowledgements

The work described here would not have been possiblewithout the full support of the PTCS project team.Current team members include: Joe Brandt, Jeff Cromer,Ray Creager, Paul Marganian, Melinda Mello,J.D. Nelson, Jason Ray and John Shelton. Wegratefully acknowledge assistance with the surfacemeasurements from Claire Chandler, Ron Maddalena,Fred Schwab, Bojan Nikolic, Richard Hills, andJohn Richer. We would also like to acknowledge theprevious NRAO staff members, the constructioncontractors Lockheed-Martin and its predecessors, andothers who have delivered us such a delightful antennato work with.

R. M. Prestage, K. T. Constantikes,D. S. Balser, J. J. Condon

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Figure 1. Amplitude and phase plots for the calibration source NRAO530 for theLos Alamos to North Liberty (top) and Los Alamos to Green Bank (bottom) baselines.

The Green Bank Telescope Joins 7-mm VLBI Community

One of the key intermediate goalsfor the Green Bank Telescope,and the GBT Precision TelescopeControl System Project, was todeliver usable Q-band (43GHz,7mm) telescope performance bythe Winter of 2003/04. Thiscapability was achieved inDecember 2003. In conjunctionwith use of the active surface,the crucial new developmentwas the implementation ofautomated real-time correctionsto pointing and focus, to compen-sate for the effects of thermalgradients in the antenna structure(see accompanying article). Thiscorrection system has been inproduction use, to great effect,since February 2004.

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The first class of science to make use of this newcapability has been 7 mm VLBI, with observations per-formed in March and April 2004. Mapping of Sgr A*was the object of project BS131 (Shen et al), and theM84 jet was observed in project bw070 (Walker et al).Sgr A* will again be studied by Bower et al. in May.

Under good weather conditions (clear skies and windsbelow 5 mph) the telescope performance is very good,as shown in the accompanying correlator plot. Thisfigure shows results for the calibration sourceNRAO530 in project BS131. The upper two panelsshow the results from the LA-NL baseline (Los Alamosto North Liberty), and the large arrow shows thetypical correlated amplitude is about 300 counts.The lower two panels show the results from LA-GB(Los Alamos to the GBT), and the correspondingamplitude is about 1200 counts. Since the geometricarea of the GBT is 16 times that of a VLBA antennaand the fringe amplitude is proportional to the geomet-ric mean of the collecting areas, we conclude that theGBT aperture efficiency equals that of the NL VLBAantenna, about 40 percent. This is quite consistentwith our independent direct measurements.

The inclusion of the GBT in VLBI observationsprovides many advantages. One is the immediateincrease in sensitivity noted above. Another is that theinclusion of a large antenna such as the GBT improvesthe ability to use self calibration. Finally, inclusion ofthe GBT can significantly improve the UV coverage,either directly by providing additional baselines, orindirectly by allowing the self-calibration of otherantennas which contribute N-S resolution.

In summary, the addition of the GBT to the VLBInetwork will make possible observations of unprece-dented high sensitivity, and we look forward to thedelivery of many exciting new science results.

R. M. Prestage, F. D. Ghigo

GBT Student Support Program:Announcement of Awards

Three awards were made in April as part of the GBTStudent Support Program. This program is designed tosupport GBT research by graduate or undergraduatestudents at U.S. universities, thereby strengthening theproactive role of the Observatory in training new gen-erations of telescope users.

The April awards were in conjunction with approvedobserving proposals submitted at the February dead-line. Awards were made for the following students:

New applications to the program may be submittedalong with new GBT observing proposals at anyproposal deadline. For full details, restrictions, andprocedures, select “GBT Student Support Program”from the GBT astronomers page. For a cumulativerecord of past awards under this program, select “GBTStudent Support Status” from the GBT astronomerspage.

J. M. Dickey (U Minn)J. E. Hibbard, P. R. Jewell, F .J. Lockman,

J. M. Wrobel (NRAO)

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P. Kondratko (Harvard U) in the amount of$35,000 for the proposal entitled “Anchoring theExtragalactic Distance Scale”.

M. Krco (Cornell U) in the amount of $33,000for the proposal entitled “GBT Observations ofNarrow HI Absorption as a Probe of MolecularCloud Evolution”.

P. Demorest (UC Berkeley) in the amount of$17,000 for the proposal entitled “PrecisionTiming of Binary and Millisecond Pulsars”.

July 2004 Socorro Issue 100

GENERAL: Please use the most recent proposal cover-sheets, which can be retrieved at http://www.nrao.edu/administration/directors_office/tel-vla.shtml for theVLA and at http://www.nrao.edu/administration/directors_office/vlba-gvlbi.shtml for the VLBA.Proposals in Adobe Postscript format may be sent [email protected]. Please ensure that the Postscriptfiles request US standard letter paper. Proposals mayalso be sent by paper mail, as described at the webaddresses given above. Fax submissions will not beaccepted. Finally, VLA/VLBA referee reports are nowdistributed to proposers by email only, so pleaseprovide current email addresses for all proposal authorsvia the most recent LaTeX proposal coversheets.

VLA: The maximum antenna separations for the fourVLA configurations are A-36 km, B-11 km, C-3 km,and D-1 km. The BnA, CnB, and DnC configurationsare the hybrid configurations with the long north arm,which produce a circular beam for sources south ofabout -15 degree declination and for sources north ofabout 80 degree declination. Some types of VLAobservations are significantly more difficult in daytimethan at night. These include observations at 90 cm(solar and other interference; disturbed ionosphere,especially at dawn), deep 20 cm observations (solarinterference), line observations at 18 and 21 cm (solar

interference), polarization measurements at L-band(uncertainty in ionospheric rotation measure), andobservations at 2 cm and shorter wavelengths in B andA configurations (tropospheric phase variations,especially in summer). Proposers should defer suchobservations for a configuration cycle to avoid suchproblems. In 2004, the A configuration daytime willinvolve RAs between 11h and 20h. In 2005, the B con-figuration daytime will involve RAs between 21h and04h. Current and past VLA schedules may be found athttp://www.vla.nrao.edu/astro/prop/schedules/old/. EVLAconstruction will continue to impact VLA observers;please see the web page at http://www.aoc.nrao.edu/evla/archive/transition/impact.html.

Approximate VLA Configuration Schedule

VLBA: Time will be allocated for the VLBA on intervalsapproximately corresponding to the VLA configurations,from those proposals in hand at the correspondingVLA proposal deadline. VLBA proposals requestingantennas beyond the 10-element VLBA must justify,

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Configuration Starting Date Ending Date Proposal Deadline

D 18 Jun 2004 30 Aug 2004 2 Feb 2004A(+PT) 17 Sep 2004 10 Jan 2005 1 Jun 2004BnA 21 Jan 2005 14 Feb 2005 1 Oct 2004B 18 Feb 2005 23 May 2005 1 Oct 2004CnB 03 Jun 2005 20 Jun 2005 1 Feb 2005C 24 Jun 2005 19 Sep 2005 1 Feb 2005DnC 30 Sep 2005 17 Oct 2005 1 Jun 2005D 21 Oct 2005 03 Jan 2006 1 Jun 2005A(+PT?) 20 Jan 2006 01 May 2006 3 Oct 2005

VLA Configuration Schedule; VLA/VLBA Proposals

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2004 C D D,A A2005 A,B B,C C D2006 A A,B B,C C


quantitatively, the benefits of the additional antennas.Any proposal requesting a non-VLBA antenna isineligible for dynamic scheduling, and fixed datescheduling of the VLBA currently amounts to onlyabout one quarter of observing time. Adverse weatherincreases the scheduling prospects for dynamicsrequesting frequencies below about 10 GHz. When theVLA-Pie Town link is in use during the VLA’s A con-figuration, we will try to substitute a single VLAantenna for Pie Town in a concurrent VLBA dynamicprogram. Therefore, scheduling prospects will beenhanced for VLBA dynamic programs that canaccommodate such a swap. See http://www.aoc.nrao.edu/vlba/schedules/this_dir.html for a list of dynamicprograms which are currently in the queue or wererecently observed. VLBA proposals requesting theGBT, the VLA, and/or Arecibo need to be sent only tothe NRAO. Any proposal requesting NRAO antennasand antennas from two or more institutions affiliatedwith the European VLBI Network (EVN) is a Globalproposal, and must reach BOTH the EVN schedulerand the NRAO on or before the proposal deadline.VLBA proposals requesting only one EVN antenna, orrequesting unaffiliated antennas, are handled on a bilat-teral basis; the proposal should be sent both to theNRAO and to the operating institution of the otherantenna requested. Coordination of observations withnon-NRAO antennas, other than members of the EVNand the DSN, is the responsibility of the proposer.

J. M. Wrobel, B.G. [email protected]

VLBI Global Network Call for Proposals

Proposals for VLBI Global Network observing arehandled by the NRAO. There are three Global Networksessions per year, with up to three weeks allowed persession. The Global Network sessions currentlyplanned are:

Any proposal requesting NRAO antennas and antennasfrom two or more institutions affiliated with theEuropean VLBI Network (EVN) is a Global proposal,and must reach both the EVN scheduler and the NRAOon or before the proposal deadline. Fax submissions ofGlobal proposals will not be accepted. A few EVN-only observations may be processed by the Socorrocorrelator if they require features of the EVN correlatorat JIVE which are not yet implemented. Other propos-als (not in EVN sessions) that request the use of theSocorro correlator must be sent to NRAO, even if theydo not request the use of NRAO antennas. Similarly,proposals that request the use of the EVN correlator atJIVE must be sent to the EVN, even if they do notrequest the use of any EVN antennas. All requests foruse of the Bonn correlator must be sent to the MPIfR.

Please use the most recent proposal coversheet, whichcan be retrieved at http://www.nrao.edu/administration/directors_office/vlba-gvlbi.shtml. Proposals may besubmitted electronically in Adobe Postscript format.For Global proposals, those to the EVN alone, or thoserequiring the Bonn correlator, send proposals [email protected]. For Globalproposals that include requests for NRAO resources,send proposals to [email protected]. Please ensurethat the Postscript files sent to the latter addressrequest US standard letter paper. Proposals may alsobe sent by paper mail, as described at the web addressgiven. Finally, VLA/VLBA referee reports are nowdistributed to proposers by email only, so pleaseprovide current email addresses for all proposal authorsvia the most recent LaTeX proposal coversheet.

J. M. Wrobel, B. G. [email protected]

Correlator Station Positions

The station locations used on the VLBA correlatorwere updated on May 12, 2004. The new coordinatesare based on the 2004b solution from the GoddardSpace Flight Center and are a significant improvementover the coordinates, and especially the rates, that havebeen in use for several years. The 2004b solutionshould closely match the International Terrestrial

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Date Proposals Due

21 Oct to 11 Nov 2004 01 Jun 2004Feb/Mar 2005 01 Oct 2004


Reference Frame (ITRF) and should be appropriate foruse with the International Celestial Reference Frame(ICRF) source coordinates and the Earth OrientationParameters (EOP) from the USNO that are used on thecorrelator. For the first time, we are now using a con-sistent set of reference frames.

The VLA positions in the geodetic frame have beenrecalculated to match the new VLBI coordinates. TheVLA uses a unique coordinate frame that is shiftedand rotated with respect to the ITRF. VLA positionsare measured with baselines run on the VLA. Twopositions are available in both the VLA frame and in2004b — VLA station N8 and Pie Town (used by theVLA in Pie Town link observations). The new posi-tions for the VLA antennas are based on shifting theVLA frame so that N8 is at its position from the 2004bsolution, and rotating the frame in the XY plane by anempirical number, very close to the VLA center longi-tude, so that the Pie Town VLA and 2004b positionsmatch as closely as possible.

The changes in the VLBA positions were typically lessthan 10 mm in each coordinate in the positions at thereference date of 1997.0. But the rates used previouslywere based on only a small time span of data and aresignificantly different in the new solution. These arethe rates due to tectonic motion and have values oftypically a few cm per year. For correlation, the refer-ence positions are adjusted by the rates multiplied bythe time offset from the reference date. The adjustedpositions are different by up to 30 mm in each coordi-nate (typically 10 to 20 mm). What ultimately mattersis the baseline coordinates which are the differencesbetween the antenna coordinates. The magnitude ofthe vector differences between the old baselines andthose from 2004b are between 4 and 34 mm with20 mm being typical.

The accuracy of phases derived using phase referencingshould be improved by the baseline changes divided bythe wavelength and scaled down by the ratio of thesource/calibrator separation divided by a radian. Forexample, a 20 mm baseline change for a 1.3 cm wave-length observation with a 2 degree target/calibratorseparation would have phases improved by about20 degrees.

Changing the coordinates used on the correlator willaffect any long term astrometric monitoring projects.The geodesy groups use only total delays to avoidworries about such correlator changes. Other groupsfor whom this might be important should have somemechanism to adjust all of their data to commonmodels. Note that, thanks to the tectonic motions,processing with the same coordinates all the time isnot a viable option — the antennas really are moving.

For details of the 2004b solution visit the website:http://gemini.gsfc.nasa.gov/solutions/2004b/. ForEOP from Bulletin-A as used by the correlator seehttp://maia.usno.navy.mil/bulletin-a.html.

R. C. Walker

VLA/VLBA Observing for UniversityClasses or Summer Programs

Instructors of university classes in observationalastronomy or advisors of summer student programsmay request small amounts of observing time on theVLA or VLBA. A typical allotment per class orprogram would be two VLA hours and/or four VLBAhours.

To apply for this time, the instructor or advisor shouldsend a short request of one or two paragraphs [email protected]. This request should include adescription of the class or program, the range of dateswhen the class or program will meet, the most desirabledate for the observing time, plus statements that atleast ten classroom hours will be devoted to theobserving project and that sufficient computingresources will be available to the students.

Most requests will come from experienced VLA/VLBAobservers known at the NRAO. However, sometimesrequests come from instructors or advisors with noprior VLA/VLBA observing experience; in such cases,we recommend that the instructor or advisor first gainsome experience by, for example, attending a synthesisimaging summer school and/or collaborating with anexperienced colleague.

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The time allotted for student observing will becoordinated with the time allotted to normal observing,whether under regular proposals or under rapid-response-science proposals. Student time will thereforebe scheduled at LSTs where normal observing has theleast demand on the instrument. About 2 to 6 weeks inadvance, the instructor or advisor will be emailedabout which particular time slot has been allocated.Before the actual observing, the instructor or advisorshould reply stating what will be observed in theallotted time. Data acquired during student time willhave no proprietary period.

We request a short report on the outcome of theobserving project, either written jointly by the studentsor the best of the project reports tendered by thestudents as part of their classwork. This report, prefer-ably in postscript or PDF format, should be sent [email protected]. Reports on student observingtime that was scheduled after June 1, 2004, will beposted at http://www.aoc.nrao.edu/~schedsoc/.

J. M. Wrobel, B. G. [email protected]

The NRAO Data Archive has been operational for sevenmonths and allows everyone on-line access to all VLAdata and some VLBA data (http://e2e.aoc.nrao.edu/archive). Thus far over 350 users from 175 institutionshave downloaded over 7800 telescope data files. Thedownload data rate is about 100 Gbytes per month.Data files over one year old are in the public domain(see URL below for details) and accounted for 3/4 ofthe file downloads. The data files reside on a hard diskarray and provide the archive users with fast accessand downloads via FTP.

Currently the archive contains all VLA data going backto 1976, raw VLBA data going back to June 2002, andsome calibrated VLBA data going back toDecember 2002. Efforts to expand the VLBA archiveback to 1992 are underway. There is a small amountof GBT data available now from 2002 and 2003. Weintend to begin archiving raw GBT data and making itavailable within the third quarter of 2004.

In the figure below, the coverage of VLA data in thearchive is shown. The total integration time of the

The Status of the NRAO Data Archive

The coverage ofVLA data in thearchive is shown.The total integrationtime of the VLA persquare degree isplotted from under300 seconds (black)to over 10000 sec-onds (white). Everysquare degree on thesky above -40 degreesdeclination has beenobserved by the VLAand is in the DataArchive.


VLA per square degree is plotted from under 300 sec-onds (black) to over 10000 seconds (white). Everysquare degree on the sky above -40 degrees declinationhas been observed by the VLA and is in the DataArchive.

A new NRAO-wide data archive policy has beenwritten and may be found at http://www.nrao.edu/administration/directors_office/dataarchive.shtml. Thenew policy shortens the proprietary period from18 months to 12 months. This is in line with propri-etary periods at other major observatories.

The development of the NRAO Archive is proceedingin phases. The first phase is essentially complete, thatis, we now provide users with access to all VLA dataand tools to identify and download the data that they’re

interested in. The next phase is to make the archivescientifically more useful to a wider range ofastronomers, especially non-radio astronomers. To thatend, a group in Socorro is discussing several issues:improvements to the user interface, more descriptivedisplay tables and automated data reduction pipelinesthat will produce calibrated data and useful images.

We would like to encourage people to use the archive,experiment with it, and send comments andsuggestions to either [email protected] [email protected]. The web page at http://e2e.aoc.nrao.edu/archive/archivefuture.html contains an outline of whatwe think is important to develop in the near future.

J. M. Benson, D. A. Frail, G. B. Taylor

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Configuration No. Proposals Hr. Requested Hr. Allocated

A 2 640 240B 1 400 0C 3 524 24D 0 0 0

Hybrid arrays 0 0 0All 1 495 ~240

ALL VLA 4 2059 ~504VLBA 1 336 336

The Large Proposal Review Committee for the VLAand VLBA met in late April to consider large proposalssubmitted at the deadline of February 2, 2004. ThisCommittee is made up entirely of scientists fromoutside the NRAO, who consider the broad scientificimpact of large observing proposals in their deliberations.At their April meeting, the Committee evaluated fourlarge VLA proposals and one large VLBA proposal.They were advised of the proposals’ logistical impacton other VLA and VLBA observing by the AssistantDirector for Socorro Operations, but otherwise actedindependently in arriving at their recommendations.

In the end, it is the intent of the NRAO to implementall the recommendations of the Committee.

The single submitted VLBA proposal was accepted forall its requested time. Of the four VLA proposals,one was accepted for all its requested time, one wasaccepted for part of its requested time, and two wererejected.

The table below gives the amount of time requestedand allocated for the large proposals, with the VLAproposals broken down by configurations:

VLA and VLBA Large Proposal Results


Note also that the upcoming VLA configuration cycle,from approximately September 2004 through January2006, has time reserved for previously allocated largeproposals. These include 120 hours in C configurationfor AK563, 121 hours in BnA configuration and212 hours in B configuration for AP452, 89 hours inB configuration for AW605, and 40 hours in B orBnA configuration for AH810. For identification ofthese proposals and more information, see the LargeProposal web page cited below.

As a reminder to prospective proposers, VLBA largeproposals may be submitted at any of the standardNRAO deadlines. The next deadline for VLA largeproposals will be June 1, 2005. Potential proposersshould be aware that this VLA deadline will cover the

configuration cycle from January 2006 throughMay 2007, during full production mode and outfittingof the EVLA at a rate of 4-6 antennas per year.Therefore, one might expect the total amount ofobserving time, and the number of available antennas,to be reduced somewhat. More detailed predictions willbe made available as the June 2005 deadline drawsnearer.

Additional information about the large proposal process,and links to results from previously scheduled large pro-posals, may be found at http://www.vla.nrao.edu/astro/prop/largeprop/.

J. S. Ulvestad

Page 14

Below, we list the proposal codes, investigators, and proposal titles for which observing time was granted via thereview process:

AK583, Kulkarni et al., “Cosmic Explosions.” 20 hours of VLA time allocated per month,beginning after the successful completion of scientific checkout for the Swift satellite.

AS801, Schinnerer et al., “The COSMOS Deep 1.4 GHz Imaging Survey: Probing CosmicEvolution in the Radio Domain.” 240 hours of VLA A configuration and 24 hours of VLA Cconfiguration allocated.

BL123, M. Lister et al., “The MOJAVE Program: Monitoring of Jets in AGN with VLBAExperiments.” 14 VLBA sessions of 24 hours each, allocated at monthly intervals.

July 2004 In General Issue 100

New VLSS Data Release Now Available

The VLA Low-frequency Sky Survey (VLSS,formerly known as 4MASS), is an ongoingeffort to map an area of 3π sr coveringthe entire sky above a declination of-30 degrees, at a frequency of74 MHz (400 cm) see April 2004Newsletter for discussion of thescience. The survey has 80"resolution and an averagedetection limit of 0.5 Jy/beam(5σ). These observations arepossible due to the new74 MHz system on the VLAas well as various new datareduction algorithms whichcan now handle the challengesof RFI and ionospheric distor-tions at this low frequency. TheVLSS is being conducted as aservice to the astronomicalcommunity and all data products arebeing made publicly available as soonas they are reduced and verified.

The first major data releasefor the VLSS is now publiclyavailable at the VLSS web-site (http:// lwa.nrl.navy.mil/VLSS), which is also linked from the NRAO homepage.Previously only data from regions observed during testobservations were available, comprising under 10 per-cent of the total survey region. The new release includesmaps and catalogs for all observations conducted so far,totaling roughly 50 percent of the eventual surveyregion. The images are available as a set of 14°×14°images distributed on a grid such that adjacent imagesoverlap by at least 2 degrees. Images can also beobtained through a postage stamp server. A source cat-alog containing all ~ 32, 000 objects detected at the 5σlevel is available in its entirety or through our search-able catalog browser.

Our next round of observations will take place in early2005, and we expect to have that data reduced, verified,and released publicly toward the end of that year. Atthat point the survey will be roughly 90 percentcomplete, with only regions in the far south (below-10 degrees) and various high noise fields (due mainlyto an over-active ionosphere) remaining to be observed(or re-observed).

The scientific goals of this survey are multiple.Samples of sources with steep spectral indices at lowfrequencies can be used to detect pulsars, high redshiftradio galaxies, and cluster halos and relics. Using these

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IN GENERAL

The blue regions indicate the current sky coverage of the VLSS. Maps and source catalogs of anyarea in this region are now available at the VLSS website (http://lwa.nrl.navy.mil/VLSS).


A small workshop commemorating the 30th anniversaryof the discovery of SgrA*, the radio source associatedwith the supermassive black hole at the center of ourGalaxy, was held in Green Bank, WV, on March 25thand 26th. There were 60 participants from a variety ofinternational and national institutes and many of theNRAO scientific staff. The program consisted of a dayand a half of scientific talks, a banquet, and a ceremonyand dedication of a plaque on the 45 Foot Telescope bythe original discoverers. A reception for all participantsand Green Bank staff followed at the Green BankScience Center.

The discovery of the compactradio source at the center of theMilky Way was made byBruce Ballick and Bob Brownin February 1974. They hadoriginally been searching forcompact regions of star forma-tion in the vicinity of theGalactic Center. The placementof the 45 Foot Telescope nearHuntersville, W V as the 35 kmoutstation for the NRAO GreenBank radio link interferometer(consisting of three 85 Footantennas at Green Bank), wascrucial for resolving out theextended confusion from SgrAWest and providing spatial reso-lutions of 0.3" (at 3.7 cm) and0.7" (at 11 cm) and detectingthe very compact radiosource, SgrA*.

An opening review talk on massive objects at thecenters of galaxies was given by Roger Blanford(Caltech), followed by a series of historical talks givenby the original observers, Bruce Ballick (U Washington)and Bob Brown (NAIC), and the Green Bank sitedirector at that time, Dave Hogg (NRAO). A numberof fascinating letters from Ballick to Brown wereshown which provided additional insight into thedetails of the discovery (also summarized recently byGoss, Brown & Lo, 2003, Astron. Nachr. S1, 1).Roy Booth (OSO), K.Y. Lo (NRAO) and Ron Ekers(ATNF) also presented accounts of early work on thesize and structure of SgrA* based on some of the first

low frequency data it is also possible to study absorp-tion effects in supernova remnants, normal galaxies,and in HII regions in the Galactic plane. Another maingoal of this survey is to make a low frequency counter-part to the NVSS, which will be available for publicuse by all astronomers. Finally we will produce a lowfrequency sky model which can be used to plan andcalibrate more sensitive 74 MHz VLA experiments, as

well as providing an initial calibration grid for plannedradio telescopes such as the SKA and LOFAR.

Wendy Lane and Aaron Cohen,(Naval Research Laboratory)

Survey done in collaboration with Rick Perley,Bill Cotton, Jim Condon (NRAO),

Namir Kassim, Joseph Lazio (NRL),and Bill Erickson (UMD)

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Bob Brown (left) and Bruce Balick (right) at the 45 Foot Telescope, which provided the cru-cial baseline for their discovery of SgrA*.

Green Bank Conference on the Discovery of Sag A*


aperture synthesis studies at Jodrell Bank, OwensValley Radio Observatory, and the VLA.

Following the historical talks on SgrA*, a series oftalks on recent results were presented. Don Backer(UC Berkeley) gave an overview of interstellarscattering properties toward SgrA*, and Geoff Bower(UC Berkeley) and Zhi-Qiang Shen (ShanghaiObservatory) reported on VLBA closure phase tech-niques used to constrain the size of this compactsource. Results on the linear and circular polarizationof SgrA* were given by Geoff Bower (UC Berkeley).Variability of SgrA* on a number of timescales is nowconfirmed across the spectrum from radio — Zhao (CfA),Bower (UC Berkeley), Herrnstein (AMNH)) tonear-IR — Ghez (UCLA), Genzel (MPIfA), Schoedel(Cologne) to X-rays — Baganoff (MIT). Progressreports by Ramesh Narayan (CfA), Sera Markoff (MIT),Eliot Quataert (UC Berkeley) and Fulvio Melia(U Arizona) followed, describing the various modelsto explain the spectrum, polarization and variability ofSgrA*. Perspectives on the current state and character-istics of the modeling were given by Heino Falcke(MPIfA). The stellar and intersetllar environmentsurrounding SgrA* was discussed in a series of talkson Friday morning. The scientific talks concluded atnoon with a thoughtful review by Mark Morris (UCLA).

Following the scientific program, a dedication ceremonywas held at the 45 Foot antenna, where NRAO DirectorFred Lo presented Bruce Ballick and Bob Brown withcommemorative framed posters (see picture). A plaqueon the 45-foot antenna and an informational adjacentsign for visitors were unveiled. An informal scientificsession was held on Friday evening to discuss prospectsfor future millimeter and sub-millimeter VLBI obser-vations of SgrA*. The next generation of telescopeswill provide an excellent opportunity for imaging onthe scale of the event horizon, allowing for detailedtests of accretion models and general relativity. The scientific program, PDF and PPT versions of thetalks, and photographs are available on the web at:http://www.aoc.nrao.edu/~gcnews/GCconfs/SgrAstar30/index.html.

Cornelia Lang(U. Iowa)

From the Spectrum ManagerThe NRAO made three FCC filings in recent months,on matters ranging from Ku-band satellite uplinks onships — we requested exclusion zones around theMauna Kea and St. Croix VLBA stations — to redefiningthe meaning of RFI (the “interference temperature”metric) and allowing use of higher power unlicenseddevices in remote areas (so-called “cognitive radio”technology). In another initiative occasioned by FCCactivity (some might call it hyper-activity) theObservatory is in the process of contacting all the localpower operators supplying the NRAO antennas toassess their plans for deployment of Broadband OverPower Lines, aka BPL. This new service, which theFCC has decided to allow under very slightly modifiedPart 15 rules governing unlicensed devices, holds greatperil for the passive and services, amateur radio, andemergency communications. The question now,though, is not whether but when large-scale deploymentwill begin.

Although some of the most important issues are still atL-band and below — the 1720 MHz OH line nowfinds itself squarely in the middle of a large swath ofspectrum re-aligned for cell phone use; Iridium is peti-tioning to expand its ~1620 MHz frequency allocationdownward; and BPL will increasingly make its wayonto the scene — K-band and mm-wave spectrum areincreasingly under pressure. The FCC has alreadyapproved the use of 24 GHz short-range radar on cars;your next one may have more microwave transceiversthan airbags. The FCC has also approved guidelinesfor unlicensed use of so-called ultrawideband (UWB)devices, one example of which is to use the entire3-10.6 GHz spectrum to send HDTV from one end ofyour house to the other. And point-to-point 76 GHzmicrowave links will soon be available free on a first-come-first-served basis at a national website.The Observatory has instituted an email discussiongroup on RFI matters, to which all interested passiveusers of the spectrum are invited to subscribe online at:http://listmgr.cv.nrao.edu/mailman/listinfo/RFIWatch.

The NRAO now also hosts, quarterly (approximately),a free-to-call-in national telecon during which wehave free-ranging discussion of RFI- and spectrum

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management-related issues. The next will be held inearly September: interested parties should subscribe toRFIWatch or send to [email protected] a request to benotified.

H. S. LisztScientist and Spectrum Manager

Color Figures in ProposalsWe are pleased to announce a formal policy in whichthe NRAO will once again accept color figures as partof the proposals for VLA, VLBA, and GBT. Due tolimitations in our ability to duplicate all our proposalsin color, or to select out specific pages to be printed incolor, we are adopting the following rules for such sub-mission.

We wish to remind proposers that this procedure placessome extra burden on the referees, by asking them to

download the appropriate color figures from the web.However, all options that involve paper distribution ofthe color figures from the NRAO are administrativenightmares in an era of electronic proposals. Since it isan additional task for the referees, we cannot guaranteethat the color figures actually will be accessed.Therefore, we suggest that proposers use color figuressparingly, and only if they are essential to the scientificjustification; an over-reliance on unnecessary color fig-ures is unlikely to endear a proposer to the referees!

J. S. Ulvestad, P. R. Jewell

2004 Summer Student Class

By the time this newsletter hits the stands, the 2004summer student class should have reported to theirassigned NRAO sites. The 2004 class consists of24 students: 14 undergraduate students supported bythe National Science Foundations “ResearchExperience for Undergraduates” (REU) program; twoundergraduate students or graduating seniors supportedby the NRAO Undergraduate Summer Studentprogram; and eight graduate students supported by theNRAO Graduate Summer Student program. Elevenstudents are assigned to Socorro, eight toCharlottesville, and five to Green Bank. These 24 stu-dents were chosen from 146 applications.

During their 10-12 week summer internship, the stu-dents will work with an NRAO advisor on a project inthe advisor’s area of expertise. Besides their summerresearch projects, the students will attend a lectureseries and go on field trips to other observatories.Students assigned to Socorro will collaborate on aVLA and VLBA observational project and attend theSynthesis Imaging Summer School. Students assignedto Green Bank or Charlottesville will have the opportu-nity to work on a GBT observational project.

The accompanying table lists the names and schools ofall 2004 summer students, together with their NRAOadvisor, site, and project title. More detailed descrip-tions of the student projects are available at http://www.nrao.edu/students/NRAOstudents_projects04.shtml.Details on these and all NRAO student programs areavailable at http://www.nrao.edu/students/.

J. Hibbard

The electronic proposal should include a legiblegrey-scale version of the color figure. The NRAOwill only distribute black-and-white versions ofproposals to the referees on paper.

If the proposer wishes a color version of the figureto be available to the referees, he/she should addto the figure caption language such as “Color ver-sion of this figure is available on line at NRAO.”

Proposers should inform the relevant NRAO per-sonnel of the existence of a color figure, anddeposit that figure with NRAO. For the GBT, thismay be done by including the figure as a separateattachment using the Proposal Submission Tool.For the VLA and VLBA, proposers should waituntil they get an acknowledgment that includes thecode assigned to the proposal. Then, they shouldlog in to NRAO via anonymous ftp, change todirectory pub/incoming/Proposals/colorfigs, anddeposit the figure. They should use the namingconvention “XXnnnn-Fign.ps” where “XXnnnn”is the proposal code, such as AB1023 or BN043.The “n” in “Fign” should be replaced by theFigure number.

Color figures will be made available to the refer-ees via a private URL, so that they may view thefigures when reviewing a proposal.

(1)

(2)

(3)

(4)

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PARTICIPANT SCHOOL PROJECT ADVISOR SITE PROGRAM

Patrick California Institute Radio Observations Dale Frail SOC NRAOCameron of Technology of Gamma-ray Burst GRP

Afterglows

High ResolutionUniversity of Imaging of Yancy

Jana Grcevich Wisconsin-Madison Formaldehyde Shirley SOC NSF REUEmission TowardsPre-protostellar Cores

Nicole Lycoming College The Evolution of Greg Taylor SOC NSF REUGugliucci Radio Galaxies

Kelley Hess Cornell University Radio Sources in the Lorant SOC NSF REUAndromeda Galaxy Sjouwerman

University of A Test SpectrometerBradley Isom Nebraska-Lincoln for the Green Bank John Ford GB NSF REU

Electronics Division

University of Broadband DigitalSarah Jaeggli Arizona Spectrograph for the Rich Bradley CV NSF REU

GB/SRBS

University of SoftwareCarlos Kelly Alaska, Fairbanks Development for the Jim Pisano CV NRAO

ALMA Correlator GRP

University of VLA Observations of Ken CV NRAOJohn Kelly Virginia the Chandra Deep Kellermann GRP

Field South

Mariana Sweet Briar TurbulentLazarova College Characteristics of Tony Minter GB NRAO

Galactic HI uGRP

ResearchMarsha Logan Benedict College Opportunities in Solar Tim Bastian CV NRAO

Radiophysics GRP

University of Investigating the Craig NRAOChun Ly Arizona Structure of Radio Walker SOC GRP

Jets

University at The Life of Young Yuri GB NSF REUAnn Martin Buffalo Radio Jets Near Kovalev

Black Holes

Data ReductionDanielle Miller James Madison Involving Nicole GB NSF REU

University Higher-Dimensional Radziwill

2004 NRAO Summer Students


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PARTICIPANT SCHOOL PROJECT ADVISOR SITE PROGRAM

Rebecca Villanova University Automated 600 - Eric Percy 720 GHz Receiver Bryerton CV NSF REU

Measurements

Automation HardwareLin Qiu University of Development for John Effland CV NRAO

Wisconsin-Madison ALMA Receiver uGRPEvaluation

North CarolinaLynnae Quick Agricutural and Radio Observations Rachel Osten CV NSF REU

Technical of Brown DwarfsUniversity

Urvashi Rao University of A New Deconvolution Tim SOC NRAOVenkata California, San Diego Algorithm Cornwell GRP

Kirstin Clarkson University The Jets of the Vivek SOC NSF REUSchillemat Microquasar SS433 Dhawan

A Search for ExplosiveSarah Scoles Agnes Scott College Radio Transients in the Glen GB NSF REU

VLA Data Archive Langston

Optimization of ScaleAnandkumar New Mexico Tech Sensitive Sanjay SOC NRAOShetiya Deconvolution Bhatnagar GRP

Algorithms

Christine Water Masers in the Mark Simpson Wellesley College FU Orionis Object Z Claussen SOC NSF REU

Canis Majoris

Prototype Design of aNew Orthomode Shing-Kuo

David Stewart Virginia Tech Transition Based on Pan CV NRAOthe Active Balun GRPTechnique

Observations of theSunyaev-Zeldovich

Adrienne Stilp University of Effect in Clusters of Steve Myers SOC NSF REUWisconsin-Madison Galaxies with the

Cosmic BackgroundImage

Willamette Time Evolution in the ShamiBen Zeiger University Supernova Remnant Chatterjee SOC NSF REU

STB 80

2004 NRAO Summer Students (continued)


Page 20

A Change in Editor for the NewsletterIt is exactly 23 years ago this month that the first issueof the NRAO Newsletter appeared, having beenfounded by Mort Roberts, then Director, with myselfappointed as Editor. In June 1981, there was only oneother astronomical newsletter (ESO’s Messenger) andnone other that could be nicknamed the Yellow Peril(the color of the NRAO Newsletter was intended to begold). Over time, we graduated from single-column todouble-column, from matte to glossy, and greeted thenew millennium (January 2000) with full color. Thesubject matter had evolved from a narrow emphasison purely technical matters to the present inclusion ofscience, for which John Hibbard, Juan Uson, andJim Condon have served as associate editors forscience. They have provided a wealth of stimulatingscience featuring the results of NRAO facilities, andincluding images of technically superb quality. Oursubscription list grew from about 400 to 1247 atpresent. The current budget for four issues per yearis ~$15,000.

After nearly a quarter century, it comes time tomodernize once again, this time with the Editor. Thepresent issue is the 100th, which seems to be a goodnumber for me to bow out with. After nearly a quartercentury, it is time to pass the editor’s job to someonenew. Thus, beginning with the October 1 issue,Mark Adams, recently hired as the Assistant to theDirector, will begin his tenure as editor. I’d like toexpress my great appreciation for the many peoplewho have made the Newsletter possible. Theseinclude those who contributed articles over the years(in some cases a great many), and those who helpedwith the production of the Newsletter. The list is long,but in addition to the Science editors, I would like tosingle out Sheila Marks and Patricia Smiley. Pat hasbeen with the Newsletter since 1981 and her graphicarts skills have been indispensable. It has been apleasure to work with all.

Barry Turner, Editor


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July 2004 New Results Issue 100

NEW RESULTS

This year is the 30th anniversary ofthe discovery of Sagittarius A*(Sgr A*), the compact radio sourceassociated with the massive black holeat the center of the Milky Way.Since that time, Sgr A* has been thetarget of numerous observations atradio, infrared, and X-ray wavelengthsand much has been learned. Theproper motions of stars in the GalacticCenter, for instance, have demonstratedconclusively that the mass of theobject is 4 million times the mass ofthe Sun (Ghez et al. 2004).

In spite of this progress, much is stillunknown about Sgr A*. In particular,we have yet to achieve the most basicof results: an image of the sourceitself. This problem has remainedthorny because of the presence ofturbulent interstellar plasma along theline of sight from the Earth to theGalactic Center. This turbulent plasma scatters theradio waves produced by the source. The resultantimage is an ellipse with a size that scales quadraticallywith wavelength. From 20 cm to 0.7 mm wavelength,the apparent size of Sgr A* decreases from 0.5 arcsecto less than 1 milli-arcsec. Since the effects of scatter-ing weaken substantially with decreasing wavelength,observations have been pushed to short wavelengths.A combination of the effects of water vapor in theatmosphere and poor antenna performance makecalibration challenging in this regime, leading touncertainty over the quality of the image.

We have recently used a non-standard technique, closureamplitude analysis, to study new and archival observa-tions of Sgr A* obtained with the Very Long BaselineArray (Bower et al. 2004). Our technique is robust

against many of the problems of short-wavelengthobserving. Essentially, closure amplitude analysisforms a quantity that is independent of amplitude cali-bration. The result is less precise but more accuratethan what is found with traditional calibration. Wecompensate for the lack of precision by using a largenumber of experiments, 19 in total, to achieve a moreaccurate and more precise result.

The VLBA data span 6 cm to 0.7 cm wavelength.Combining the VLBA data at 2 cm and longer wave-lengths with archival Very Large Array data at 20 cm,we are able to make a highly accurate calibration of thescattering law. We difference our measured size fromthe expectation of the scattering law to obtain a meas-urement of the intrinsic size of the source at 1.3 cmand 0.7 cm wavelength (see figure). The intrinsic size

Detection of the Intrinsic Size of the Galactic-Center Black Hole Radio Source,Sagittarius A*

Major-axis size, minor-axis size, and position angle (deg) of Sgr A* as a function ofwavelength normalized by a λ 2 scattering law (solid line). The deviation in the shortwavelength sizes from the scattering law are the indication of the presence of theintrinsic source. We include a 3.5 mm measurement of the major axis, also made withclosure-amplitude techniques (Doeleman et al. 2001).

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is 24 ± 2 Schwarzschild radii at 0.7 cm, where oneSchwarzschild radius is the size of the event horizonof a four million solar mass black hole. This is thehighest-resolution observation of any black hole systemin units of the event horizon. We can use the size andthe upper limit to proper motion of the black hole(Reid et al. 2003) to derive a lower limit to the massdensity of the black hole: 40,000 solar masses percubic astronomical unit (1 AU = 150 million km).

The intrinsic size decreases strongly with decreasingwavelength. If the power-law that we observe continuesto even shorter wavelengths, then the source willbecome comparable to the event horizon scale around awavelength of 1.3 mm. On this scale, the image willbe severely distorted by propagation effects in thestrong gravity of the black hole (Falcke, Melia, & Agol2000). Radiation traveling close to the black hole willbe gravitationally lensed and appear in a ring with aninner radius of five Schwarzschild radii. Detection ofthis ring will be the tightest constraint ever placed on

the mass density of a black hole. Details of the imagemay reveal information about the spin of the black hole.Plans are underway to conduct the next-generationexperiment to observe this effect. The experiment willrely on an ad hoc network of millimeter and submilli-meter wavelength telescopes including the AtacamaLarge Millimeter Array in Chile. While technicallyvery challenging, this exciting experiment will provideus ultimately with the closest look at physics in thestrong gravity of a black hole.

Geoffrey C. BowerUC Berkeley

References:

Ghez, A. et al. 2004, ApJL, 601, 159Bower, G. C., Falcke, H., Herrnstein, R. M., Zhao,

J. H., Goss, W. M., & Backer, D. C. 2004, Science, 304, 704

Reid, M. et al. 2003, Astron. Nachr., 324, S1Falcke, H., Melia, F., & Agol, E. 2000, ApJL, 528, 13Doeleman, S. S. et al. 2001, AJ, 121, 2610


Between every astronomer and the extragalactic universestands the interstellar medium of our own Galaxy, theMilky Way, which can obscure, confuse, and impedeattempts to peer through it. This is a special problemat wavelengths most affected by emission or absorptionsince there is no direction from Earth to extragalacticspace which is completely free of interstellar gas anddust.

The Spitzer Space Telescope (formerly called SIRTF)is the last of NASA’s four “Great Observatories.” It waslaunched into an Earth-trailing solar orbit in August2003 to obtain images and spectra in at infrared wave-lengths between 3 and 180 microns. Its earliest sciencemission is the “First-Look” Survey (FLS) covering anarea of about five square degrees — a deep view of theextragalactic sky in the far-infrared at sensitivitiesabout 100 times better than surveys with previoussatellites. Because emission from “foreground”Galactic dust can be bright at longer infrared wave-

lengths, it is important to understand this Galacticcontamination in the FLS field.

One of the best tracers of interstellar dust is interstellargas. At high Galactic latitudes, where there is littlemolecular gas, the best tracer is the 21 cm line ofneutral atomic hydrogen (HI). The total amount of gasis approximately proportional to the total amount ofdust, and the line observations can be used to distin-guish gas in clouds with different velocities.

The Robert C. Byrd Green Bank Telescope (GBT) has asignificant advantage for measuring 21 cm emission athigh Galactic latitudes, where the emission is alwaysextended and often quite weak. Most radio telescopeshave feeds, subreflectors, and support legs partiallyblocking their main mirrors, and they scatter “stray”HI radiation from unwanted directions into the feeds.These structures are offset on the asymmetric GBT sothe aperture is unblocked and the amount of strayradiation confusing the desired signal is reduced.

Comparing Dust and Gas In Interstellar Space

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However, there is still some stray radiation from for-ward spillover around the subreflector which weattempted to subtract to make an accurate image of thespectra and sky distribution of HI in the FLS field with9.2 arcmin resolution. The HI spectra show emissionfrom a number of interstellar components: a high-velocity cloud, several intermediate-velocity clouds, awidespread broad-line source, and several local, coolclouds.

How do the dust and gas images compare? The leftpanel of the figure is the best image showing the totalamount of dust derived from infrared data by Schlegel,Finkbeiner, and Davis (1998). Not all HI is associatedwith infrared-emitting dust. In particular, high-velocityclouds have never been detected in the infrared, mostlikely because these distant clouds have almostprimordial chemical compositions. They contain hydro-gen and helium gas but are nearly devoid of the heavierelements (carbon, oxygen, silicon, iron, etc.) producedin stars and needed to form dust. Our HI map of theFLS field, excluding emission from high-velocity

clouds (VLSR < −100 km/s), is shown in the right panelof the figure. The detailed similarity of these HI gasand dust images is striking. A quantitative analysisshows that the dust-to-HI gas ratio does vary somewhatacross the FLS field and among spectral components.For the brighter components this suggests the presenceof molecular hydrogen in addition to atomic hydrogen.For others the variations imply an interesting variationin physical conditions across a cloud. It is clear thatthese HI data are providing new information about theinterstellar medium itself as well as estimates of theGalactic foreground contamination.

The GBT data were obtained as a service to the astro-nomical community and have been released via theweb (http://www.cv.nrao.edu/fls_gbt) for anyone to useand analyze.

F. J. Lockman and J. J. Condon

References:

Lockman, F. J., & Condon, J. J. 2004, AJ, submittedSchlegel, D. J., Finkbeiner, D. P., & Davis, M.

1998, ApJ, 500, 525


Interstellar gas is an excellent tracer of dust in the FLS area. The left panel is a false-color image of infrared-emitting dust, and the rightpanel shows the HI column density after the high-velocity emission has been subtracted. Colors ranging from dark blue to red indicateincreasing column density.

61°00'

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Right Ascension (J2000)

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Radio surveys have been extremely successful atidentifying gravitational lens systems, the most notablebeing CLASS (the Cosmic Lens All-Sky Survey)which discovered a total of 22 lens systems using datafrom the VLA, MERLIN, and the VLBA. Lens systemsresult when the radio rays from a distant source pass,en route to the earth, close to a large mass concentrationsuch as a galaxy or galaxy cluster. Gravity causes therays to be deflected and can, under certain conditions,produce multiple images of the background source.The positions and brightnesses of the various imagescan be used to measure important properties of thegalaxy doing the lensing, such as its total mass andmass distribution. Very Long Baseline Interferometer(VLBI) observations can often provide the most useful

constraints on the lens model as the high resolution canseparate the lensed images (which are usually unre-solved by smaller arrays) into additional components ifthe source contains substructure.

A good example of where VLBI observations haverevealed subcomponents in previously unresolved lensimages is the source CLASS B0128+437 (Biggs et al.2004). This was known to consist of four lensedimages from MERLIN observations, but follow-upobservations with the VLBA at 5 GHz resolved theimages into a jet having a length of ~ 30 milli-arcsecand dominated by three knots of emission in the bright-est image A (see Figure 1). This image shows theMERLIN map (center inset) indicating the positions of

the four images plus VLBAmaps of each image.B0128+437 is not a terriblybright source (CLASS sourceshave total flux densities as lowas 30 mJy), and the brightestVLBI subcomponent has a totalflux of only 4 mJy. However,the signal-to-noise ratio issufficient (off-source rmsnoise = 50 microJy/beam) thatwe can determine the positionsand sizes of each subcomponentby fitting elliptical Gaussians tothe data.

This source has also been stud-ied at other frequencies (2.3 and8.4 GHz) with the VLBAobserving in conjunction withthe 100-m Effelsberg telescopein Germany. These data haveallowed us to measure thebrightness variation with fre-quency of the subcomponents.Since gravitational lenses areachromatic, we can use thisfrequency dependence to


Detailed Radio Images Seen Through a Gravitational Lens

Figure 1. The four images A, B, C, and D as seen by MERLIN (center inset) andresolved by the VLBA (outer panels).

Page 25

determine which subcomponent in each image corre-sponds to the same source component. Figure 2 showsimage A at 2.3, 5 and 8.4 GHz (from left to right). Acomparison between the two highest frequenciesdemonstrates that the brightness of the southernmostcomponent is less variable with frequency than the others.

We have attempted to find a mass model which satisfiesthe multitude of image constraints that have beenprovided by the VLBI imaging. Prior to this a simplemodel had been constructed using the MERLIN dataalone, but since practically nothing is known about thelensing galaxy (Hubble Space Telescope observationsshow it to be extremely faint, I = 24 mag), it was notpossible to compare the model galaxy parameters withobservations. The extra constraints provided by theVLBI data, however, rule out such simple models forthe lensing galaxy as these are unable to reproduce theobserved subcomponent positions. More complicatedmodels are therefore required and an important factorin the success of this will be the acquisition ofimproved optical/infrared HST imaging with whichimportant model constraints (such as the position ofthe lensing galaxy) can be obtained.

Whereas it requires detailed modeling to reveal thediscrepancy between the observed and modeled imagepositions, immediately apparent from the VLBI map isthe difference between image B and the other three.Whilst three subcomponents can be seen in images A,C and D (the three subcomponents in C are revealed inmaps of higher resolution), image B (figure 1) showsno apparent signs of any significant substructure. Thisimage does have the appearance of a straight jet, butthe subcomponents appear to be missing. This iscaused, we believe, by the radio radiation producingthis image being distorted as it travels through theinterstellar medium of the lensing galaxy. The result isthat the subcomponents are smeared and can no longerbe differentiated. VLBI studies of other lens systemssuggest that this phenomenon is quite common in thelens population.

Andy Biggs Joint Institute for VLBI in Europe

Reference:

Biggs, A. D., Browne, I. W. A., Jackson, N. J., York, T., Norbury, M. A., McKean, J. P., & Phillips, P. M. 2004, MNRAS, 350, 949


Figure 2. Component A at 2.3 GHz (left), 5 GHz (middle), and 8.4 GHz (right).

Page 26

Gamma-ray Bursts (GRBs) herald the most powerfulexplosions in the Universe and produce afterglows thatcan be detected for months to years at radio wavelengthsbefore they fade away. Very Long BaselineInterferometer (VLBI) observations of the nearby(z = 0.1685) gamma-ray burst GRB 030329 allowed us,for the first time, to resolve a GRB afterglow (Taylor etal. 2004). The size of the afterglow was found to be~ 0.07 mas (0.2 pc) 25 days after the burst, and0.17 mas (0.5 pc) 83 days after the burst, indicating anaverage apparent expansion rate of 3-5 times the speedof light. This apparent superluminal expansion is con-sistent with expectations of the standard fireball model(Granot & Loeb 2003, and references therein). Basedon energetics and breaks in the light curves, typicalGRBs appear to be collimated into cones of angle~ 0.1 radians (Berger, Kulkarni, & Frail 2003), whichwe must be within to see the gamma-rays. To get an

apparent superluminal expansion of 5c requiresLorentz factors of ~7 and bulk motions close to thespeed of light. The energy release estimated from themeasured expansion of GRB 030329 is 2 × 1050 ergsassuming expansion into a circumburst medium with aconstant density of 1 cm-3.

Much more difficult to explain in GRB 030329 was theemergence of an additional compact component at adistance of 0.28 ± 0.05 mas (0.80 pc) from the maincomponent (Figure 1). Assuming that it was ejected atthe time of the explosive event marked by the GRBitself, an apparent velocity of 19c would have beenrequired to reach its observed position 52 days after theburst. This is the first such “shrapnel” from a GRBexplosion to be observed. If such high-speedcomponents turn out to be commonplace, then this factwill have profound implications for the fireball models.


Resolving the Afterglow of a Gamma-ray Burst

Left: Image of GRB 030329 at 15 GHz taken with an array consisting of the VLBA, VLA, GBT, and Effelsberg telescopes. The resolution is0.25 × 0.67 mas. Contours start at 0.6 mJy/beam and increase by factors of 2. The extension to the northeast is a ~ 20σ detection of a jetcomponent. Right: The same image with a point source of 4 mJy at the position of the main afterglow component subtracted. The jet compo-nent has a flux density of 1.8 mJy.

Page 27


We measure the projected proper motion of GRB030329 in the sky to be < 0.3 mas in the 80 days fol-lowing the burst. In the relativistic fireball model ashift in the flux centroid is expected due to thespreading of the jet ejecta (Sari 1999). For a jet viewedoff the main axis the shift can be substantial. However,since gamma rays were detected from GRB 030329 itis likely that we are viewing the jet largely on axis.The predicted displacement in this case is expectedto be small (0.02 mas), and well below our measuredlimit over 80 days of 0.10 ± 0.14 mas.

In the competing “cannonball” model, the aftergloworiginates from the superluminal motion of plasmoidsejected during a supernova explosion with Γ0 ~ 1000(Dado, Dar, and De Rújula 2003). Dar & De Rújula(2003) predicted a displacement of 2 mas over the 80days of our VLBI experiment assuming plasmoidspropagating in a constant-density medium. This modelcan be ruled out based on the VLBI limit of < 0.3 mason the proper motion. A further problem for thecannonball model is that the compact plasmoids willscintillate strongly at all times, whereas inGRB 030329 there are only moderate variations seenin the radio light curves, consistent with weakinterstellar scintillation. Berger et al. (2003) derive a

model-dependent size of 0.020 mas at 15 days after theburst, consistent with the growth rate directly imagedby the VLBA starting 25 days after the burst.

The VLBI campaign to obtain these results made useof many of the largest radio telescopes on Earth includ-ing the VLBA, phased VLA, Green Bank, Effelsberg,Arecibo, and phased Westerbork telescopes. Bycorrelating the signals from all these telescopes a lownoise of 30 microJy/beam was achieved in just138 minutes on the fading GRB, 83 days after theburst. The resultant high signal-to-noise observationyielded the most secure measurement of the angularsize of the afterglow.

G. B. Taylor (NRAO)

References:

Berger, E. et al. 2003, Nature, 426, 154Berger, E., Kulkarni, S. R., & Frail, D. A. 2003, ApJ,

590, 379Dado, S., Dar, A., & De Rújula, A. 2003, A&A,

401, 243Dar, A. & De Rújula, A. 2003, GRB Circular Network,

2133, 1Granot, J. & Loeb, A. 2003, ApJ, 593, L81Sari, R. 1999, ApJ, 524, L43

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