The GLAST Mission Gamma-ray Large Area Space Telescope Omar Tibolla Padova University International...

The GLAST MissionGamma-ray Large AreaGamma-ray Large AreaSpace TelescopeSpace Telescope

Omar TibollaPadova University

International School of Cosmic Ray Astrophysics,

Erice (Italy) 20 - 27 June 2006

Large Area Telescope (LAT)

GLAST Burst Monitor (GBM)

Gamma-ray Large Area Space Telescope

-France -Germany

-Italy -Japan

-Sweden -USA

Energy Range 10 keV-300 GeV.

GLAST :

- An imaging gamma-ray telescope (LAT)

- A second instrument for the study of Gamma Ray Bursts (GBM).

Omar Tibolla. ISCRA. Erice (Italy) 20 - 27 June 2006

ACD contains 16 towers and each tower is divided in two parts:

-the TRACKER (TKR): 18 layers in each tower -Tungsten converters -2 orthogonal SSD planes of silicon microstrip sensors for detecting the electromagnetic shower(1.5 χ0 including silicon and other materials)

-a CALORIMETER (CAL) of CsI crystals dopped by Tl; so the energy deposited by the EM shower is converted in light signal. CAL is characterized by fast decaying fluorescent light (~ns) and a long decaying afterglow (~ms).

e+ e–

e+ e–e+ e–

The main instrument of GLAST is the Large Area Telescope (LAT): a pair conversion telescope:

Anticoincidence Shield (ACD) made of plastic scintillator (Bicron-408) sensitive to charged particles; ACD is segmented to avoid self veto from Calorimeter backsplash and also for micrometeorites.

TRACKER

CALORIMETER

ANTICOINCIDENCESHIELD


LAT Specifications and Performance Compared with EGRET



<0.15o (>10 GeV)



EGRET (>100 MeV)Simulated LAT (>100 MeV, 1 yr)Simulated LAT (>1 GeV, 1 yr)

Improvements from EGRET to GLAST:

The Glast Burst Monitor (GBM) will include two sets of detectors:

-12 sodium iodide (NaI) scintillators -2 cylindrical bismuth germanate (BGO)

scintillators

The NaI detectors are sensitive in the lower end of the energy range, from a few

keV to about 1 MeV and provide burst triggers and locations.

The BGO detectors cover the energy range ~150 keV to ~ 30 MeV, providing a

good overlap with the NaI at the lower end and with the LAT at the higher end.

Schematic layout of the 12 NaI and two BGO detectors on the GLAST spacecraft


Quantity BATSE GBM (Minimum Spec.)

Energy Range 25 keV - 10 MeV < 10 keV - > 25 MeV

Field of View 4π sr all sky notocculted by the Earth

Energy Resolution < 10% < 10%

Deadtime per Event < 15 μs

Burst Sensitivity 0.2 cm-2 s-1 < 0.5 cm-2 s-1

GRB Alert Location ~ 25° < 15°

GRB Final Location 1.7° < 1.5°

GBM Specifications and Performance Compared with BATSE


AGN/BLAZARS

UNIDENTIFIED EGRET SOURCES

NEW PARTICLE PHYSICS

EXTRAGALACTIC BACKGROUND LIGHT

GAMMA-RAY BURSTS

PULSARS

COSMIC RAYS AND INTERSTELLAR EMISSION

SOLAR FLARES


Scientific purposes


AGN /BLAZARsEGRET discovered that blazar-class active galactic nuclei are bright and variable sources of high-energy gamma rays.The emission is believed to be powered by accretion onto Supermassive Black Holes at core of distant galaxies.GLAST will increase the number of known AGN gamma-ray sources from about 100 to thousands.

Unidentified EGRET Sources

More than 60% of EGRET sources are Unidentified!GLAST should be able to identify them!

Considering their distribution in the sky, almost one third of these are extragalactic (=Blazars).Some should be Radio-quiet Pulsars.Recent works speak about Galactic Micro-Quasar, or also that these objects could be associated with the nearby Gould Belt of star forming regions that surrounds solar neighborhood.


New Physics

SUSY theories (in particular Minimal Super-Simmetrical Model: MSSM) state the existence of the Lightest Super-Simmetrical Particle: neutralino.

The theories predict that annihilation of neutralino and anti-neutralino should give us

a signal ( or ).


In last years they expect to be able to see this kind of signal from Galactic Center:

(GLAST Scientific Brochure, 2001) (Cesarini et al., astro-ph/0305075 v2, 2004)


New Physics (2)Recently new models have been proposed about detecting this signal better from DM mini-spikes (=clumps around intermediate Black Holes: 102 MO < MBH <106MO ) in

Galactic Halo (Bertone, Zentner and Silk, PhyRev D72, 103517) .

.

In Padova, following this model we are trying to simulate these kind of scenarios; see the spectra by Riccardo Rando’s work (work in progress): for different masses and distance of the clumps.

.


Extragalactic Background Light

The Diffuse EBL consists of the sum of the starlight emitted by Galaxies through the history of the Universe.A way to study this extragalactic background is to measure the attenuation on -ray spectra of distant extragalactic objects by these EBL photons. (see the spectra by Luis Reyes’s work on DC2)

The sensitivity of GLAST at high energies will permit the measurement of AGN spectra at high energies and so the study of extragalactic background light: thanks to the large number of AGNs that GLAST will discover, the intrinsic spectra of AGNs should be distinguishable from the effects of attenuation.


Gamma Ray Bursts

With its high-energy response and very short deadtime (very important to confirm the Standard models) GLAST will give big improvements in GRBs study.

LAT and GBM will detect almost 100 bursts per year and will provide near-real-time location information to other observatories for afterglow searches.

GLAST will measure spectra from keV to GeV energies and tracking their afterglows.

(Simulated light curve of a GRB detected by LAT

and by GBM)

(GLAST Scientific Brochure, 2001)


PULSARS

GLAST will discover many gamma-ray Pulsars, 250 or more (considering that many radio-quiet, Geminga-like, Pulsars should be discovered and that GLAST will be able to precisely search for periodicities directly in EGRET Unidentified Sources) and will provide definitive spectral measurements (in order to distinguish between the two primary models: outer gap and polar cap models)

(Geminga seen by EGRET)

(Spectra of the 2 primary models, simulated for 1 year of survey observation)


Cosmic Rays and Interstellar Emission

GLAST will spatially resolve some Supernovae Remnants and precisely measure their spectra (see the end of this talk); and it may determine whether SNRs are sources of cosmic rays.

Spatial and spectral studies of this gamma-ray emission will permit to study separately the distributions of protons and electrons; so will test cosmic-ray production and diffusion theories.

RXJ1713.7-3946 and RXJ0852.0-4622 (Vela Junior) seen by H.E.S.S. array


Solar Flares

GLAST should be able also to study Solar Flares.In fact EGRET discovered that the Sun is a source of GeV gamma rays.

Mandzhavidze and Ramaty (1992) modeled EGRET data using a composite spectrum of electron bremsstrahlung and pion decay

Thank to its Large Effective Area and its small deadtime, GLAST will be able to determine where the acceleration takes place and it should be able also to confirm (or not) if the protons are accelerated along with electrons.


And other extremely important features are the COMPLEMENTARITY WITH GROUND-BASED GAMMA-RAY TELESCOPES and that GLAST will study the Universe in UNEXPLORED REGIONS OF EM SPECTRUM.


GLAST CURRENT STATUS: Hardware16 towers were assembled last year and now LAT final assembly is complete!

Delivery of LAT for integration with the spacecraft: May 2006

GBM instruments (NaI, BGO Detectors, Power Supply Box, etc.) are ready and they have just passed through EMI and thermal vacuum tests.

GLAST integration and testing: Summer 2006 through Summer 2007

Launch: Launch Date August 2007

Launch Site Kennedy Space Center

Launch Vehicle Delta 2920H-10

Orbit 565 km Circular (i.e.; e<0.01), 28.5° Inclination

Begin Science 1-2 months after launch

Mission Duration 5 years (10 years Goal)


GLAST CURRENT STATUS: SoftwareDC2 is closed the 2nd of June 2006: http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/default.html

Data challenges are full-sky simulations. They provide excellent testbeds for science analysis software.

Full observation, instrument, and data processing simulation. Team uses data and tools to find the science. “Truth” revealed at the end.

• A progression of data challenges.– DC1 in 2004. 1 simulated day all-sky survey simulation ( 3rd EGRET Catalog), later

enlarged to a week of simulation.• find the sources, including GRBs• a few physics surprises

– DC2 NOW (kickoff 1-3 March). 55 simulated days all-sky survey.• first catalog• add source variability (AGN flares, pulsars) and extended sources (SNRs and

Molecular Clouds); add GBM; add backgrounds (charged particles and albedo ) • closeout end of May (>100 participants)

– DC3 (?) in 2007. Support for flight science production.


DATA CHALLENGE 2

In DC2 there are simulated many Galactic sources:

http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/Sky_model_Galactic_Digel_v3.ppt

And many Extragalactic sources:

http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/dc2_truth_exgal_McEnery.ppt

(DC2 Sky)


Simulated Extragalactic sources are:-Galaxies-Galaxy Clusters-AGNs-GRBs-Extragalactic Background Light

Galactic sources are summarized in this table:

# sources # gammas

Milky Way itself (=Diffuse Emission of MW) (1)

1,704,807

Pulsars (414) 140,596

Plerions (7) 9780

SNR (11) 22,592

XRB (5) 1491

OB associations (4) 295

Small molecular clouds (40)

1741

Dark matter (~2) 5158

‘Other 3EG’ (120) 112,386

Sun (1 flare) 4669

Moon (1) 10,523


During DC2 I essentially worked on SNRs: simulation and analysis.About SNRs simulation, see again:

http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/Sky_model_Galactic_Digel_v3.ppt

SNRs simulations in DC2

(SNRs in DC2 Sky)

I implemented some HESS SNRs for GLAST software, including spectral extrapolation down to energy range of LAT; (sometimes, we used also Cangaroo (I and II) and EGRET results in order to do some tests on these SNRs)


-RXJ1713.7-3946(astro-ph/0511678v2, 2005)

-HESS galactic survey (ApJ, 636, 777-797, 2006): -HESSJ1634-472 -HESSJ1640-465 -HESSJ1713-381 -HESSJ1813-178 -HESSJ1834-087

-RXJ0852.0-4622(A&A, 437, L7-L10, 2005)

Simulated SNRs:The full work was presented at Goddard Space Flight Center the 2nd of June 2006:

http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/GSFC_simulation_Tibolla.ppt


RXJ1713.7-3946: spectrumIn DC2 RXJ1713-3946 is simulated using the Broken Power Law that H.E.S.S. used to fit their experimental data:

The Break Energy is at 6.7 TeV, so for our model a single Power Law is perfectly fine and we used the lower energy part of the Broken Power Law: spectral index is 2.06 and the flux above 10 MeV integrates to 0.038 m-2 s-1 (a little smaller but very close to EGRET values).

Other test were made, using the Single Power Law spectrum proposed by Cangaroo (I e II), the Single Power Law spectrum proposed by H.E.S.S. in previous work and fluxes of the “Unidentified” EGRET source 3EG 1714-3857 (this source is very close to RXJ1713-3946, so the comparisons are immediate (see HESS paper); the total flux of 3EG 1714-3857 above 20 MeV is almost 0.03533 m-2 s-1 and it means a luminosity that is almost 1/5 of Crab luminosity, so we used this EGRET source as “the best case”) (the exempla, we will see, will follow the Cangaroo Single PL)


RXJ1713.7-3946: spatial distribution

(starting from HESS Count Map)

(and HESS simple geometrical model)

I constructed the “real physical SNRs”, using the spectral laws just seen in last slide.


Using gtobsim.exe , a scientific tool that tell us if and how each photon from “real source” interact with our instrument, we can see for example the GLAST Count Maps of that gammas (1 month of observations in “survey mode”):

(~2500 gammas, > 20 MeV) (~750 gammas, > 200 MeV) (33 gammas above 2 GeV)

(Note: the different PSFs at different energies)(In reality in DC2 the things are a little bit different, because of new IRFs with harder cut for Background Rejection, but the procedure is exactly the same)


RXJ0852.0-4622 (Vela Jr)Almost the same thing was made for Vela Jr; as I did previously, I extrapolated the total flux we should have at LAT energies, using HESS Power Law:

1.2

200

20 112

1.2

20 120 10280295.0

1 TeV

Esm

TeV

E GeV

MeV TeVMeV TeVMeVE

Almost 1/5 - 1/6 of the luminosity of the Crab.

And with this flux, I constructed again the “real physical SNRs” starting from HESS Count map:


Again, what we will see after one month of observations will be:

(2285 gammas, > 20 MeV)

(1080 gammas, > 200 MeV)

(61 gammas above 2 GeV)

So increasing the observation’s time up to 10 (5+5) years and giving a cut in energy at 2 GeV (in order to have a very small PSF) we obtain exactly the structure we had simulated before!GLAST will be able to resolve spatially such SNRs!


HESSJ1634-472

HESSJ1640-465

HESSJ1713-381

HESSJ1813-178

HESSJ1834-087

Other SNRs in inner Galaxy

http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/GSFC_simulation_Tibolla.ppt


Analysis SNRs:

And what about analysis?(also this work was presented at Goddard at same workshop, the 1st of June 2006:http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/GSFC_analysis_Tibolla.ppt )

In order to see what we can do with analysis, we go on studying RXJ0852.0-4622, that in “real life” is one of the most “unlucky” object of the sky (Note: EGRET didn’t see it):

PSR0904-5008 RXJ0852.0-4622

Vela


First question should be: “Is it a source? Or is it only a feature of the Galaxy?”Using another GLAST tool (gttsmap.exe), we can to a statistical map of this region (we model the sky including backgrounds ( also the Galaxy) and all the known sources; so the tool, analyzing each single photon, give us the probability to have a point source(!!!) there).

And we obtained a big probability to have a source there: yes, it’s a source!

Is it extended? Using the same method we see that it seem to be also extended:


We do another Statistical Map much more detailed (20-25 days of computations) and we can say that it surely extended:

And we can also see something like a structure, a structure similar to the one we simulated!

Also in this “real” case GLAST will be able to solve spatially that SNR!

(Note: the “canonical” way to search this kind of structure should be: deconvolution + cuts in energy)


And what about spectral analysis?Doing spectral analysis on that source in principle is very difficult because of its “very noisy” neighbours.We found that to study all the sources together was almost impossible. So we “isolated” and studied separately the sources; but in order to do it we had to use very small RoI, smaller than PSF ( cuts in energy).

BackgroundsExtragalactic background (fixed):constant diffuse emissionPref = 1.6 ( x 10-7)Sp. Index= -2.1

Galactic backgrounds: modeled with MapCube file GP_gamma.fitsThe scale factor is almost 1 never change very much(up to 1.037..)

Residual component:modeled with MapCube file residual.fitsThe scale factor is more than 3 times grater than we was expecting... 3.309


Vela and PSR0904-5008 PSR0904-5008

Galactic backgrounds

Residual components

Extragalactic background



Residual components

Vela

Vela fits quite well with a Broken Power Law.PSR0904-5008 with a single power law with an exponential cut-off.



Vela

Vela Jr


Residual components

PSR0904-5008

Putting all together we could analyze the SNR:

RXJ0852.0-4622 seems to fit well with a single Power Law.The work is still in progress but until now the values don’t differ too much;the extremes are: Prefactor 1 = 9769 + 982 ( x 10-9) Spectral Index 1 = -2.163 + 0.042

Prefactor 2 = 5180 + 797 ( x 10-9) Spectral Index 2 = -2.014 + 0.053

Not very far from what we have simulated!


Conclusions

About SNRs, GLAST will spatially resolve some Supernovae Remnants and precisely measure their spectra.

About GLAST, I think that, looking its scientific purposes, it doesn’t need other comments.

About the other sources, I send you again to:http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/default.html


AcknowledgementsIn alphabetic order:

- Giovanni Busetto; Padova University, Italy. - Jim Chiang; GSSC/UMBC, USA. - Valerie Connaughton; University of Alabama in Huntsville, USA. - Bernard Degrange; Ecole Polytechnique, Palaiseau, France. - Seth Digel; SLAC, Stanford, USA. - Francesco Longo; Trieste University , Italy. - Julie McEnery; GSFC, USA. - Elisa Mosconi; Padova University, Italy. - Riccardo Rando; Padova University, Italy. - Luis Reyes; GSFC, USA. - Steve Ritz; GSFC/UMD , USA. - Antonio Saggion, Padova University, Italy. - Francesca Maria Toma; Padova University, Italy. - Tracy Usher; SLAC, Stanford, USA. - John P. Wefel, Louisiana State University, Baton Rouge, USA.

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The GLAST Mission Gamma-ray Large Area Space Telescope Omar Tibolla Padova University International...

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