VLBI Monitoring of VLBI Monitoring of Gamma-Ray Blazar Gamma-Ray Blazar

PKS 0537-441PKS 0537-441

Faith Hungwe (Rhodes/HartRAO)

Dr Roopesh Ojha (NASA/GSFC)

Prof Roy Booth (HartRAO)

Outline Background

The TANAMI Program

Fermi

Results

Future Work

Background The fact that Active Galactic

Nuclei (AGN) are bright gamma-ray emitters was one of the most important results made by the EGRET instrument on board the Compton Gamma Ray Observatory.

EGRET also left us with a lot of questions about AGN, eg:

The Compton Gamma-Ray Observatory•Where are gamma-rays produced in the AGN jets with respect to the compact radio cores?•How do variability patterns relate to intrinsic jet parameters like jet speeds etc (time variability is a useful tool for linking behaviour at different wavelengths)

Background

The EGRET sources present a subset of AGN that are radio loud.

Radio observations of AGN with Very Long Baseline Interferometry resolves the powerful relativistic jets the produce the radio emission

Most theoretical models predict that gamma-ray emission is produced in the inner-most region of the jets, very close to the black hole while the radio emission is produced further downstream

PKS 0537-441 strongly variable BL Lacertae object

one of the brightest gamma-ray blazars detected in the southern sky to date.

known to be a strong intra-day variable

sometimes classified as a highly polarised quasar (Treves et al. 1993).

has been a candidate for gravitational microlensing (Romero et al. 1995)

Detected by EGRET as 3EG J0540-4402

The TANAMI ProgramTracking AGN with Austral Milliarcsecond Interferometry

TANAMI is the only parsec-scale monitoring program targeting AGN south of -30o

The TANAMI Program PI: Dr Roopesh Ojha

Observations using the technique of VLBI

Initial sample (44 sources) was selected based on previous (EGRET) gamma-ray detection and/or radio flux density monitoring observations.

Through a MoU with the Fermi collaboration, TANAMI program has since 2009 started monitoring observations of new Fermi sources

To date, more than 14 epochs have been observed and data processing is divided between members of the collaboration.

•Gamma Ray Space Telescope •Launched in June 2008 • Has 2 instruments, the Large Area Telescope (LAT) and the Gamma ray Burst Monitor (GBM)

Fermi

Fermi The main instrument

on Fermi, the Large Area Telescope (LAT) has a broader energy coverage, better resolution, a wider field of view and more sensitivity than EGRET.

Has detected 55 TANAMI sources

Observations of AGN using both Fermi and radio VLBI will likely address most of the questions the EGRET left us with.

Gamma-Ray Observations The gamma-ray observations for PKS 0537-441 were made using the

Fermi/LAT.

For each event, the Fermi/LAT measures 3 quantities, the arrival direction, the energy and the arrival time.

The gamma-ray data were reduced using Fermi science tools, using monthly time bins and an energy range of 100 MeV to 300 GeV.

The analysis is repeated for each time bin (time consuming).

Gamma-Ray Light-curve

All Fermi/LAT data shown here were downloaded from the public website http://fermi.

gsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi.

Gamma-ray light curve for PKS 0537-441 spanning approximately 21 months from August 2008 to May 2010.

•PKS 0537-441 has been reported by Fermi/LAT to be active about four times in the past two years.•In October 2008 and July 2009, by the Fermi/LAT •Feb of 2010, by AGILE•most recently (April 2010) by Fermi/LAT

•Gamma-ray light curve shows the source to be active in September 2008, July 2009 and April 2010•Monthly bin sizes were used, a possible source of the disparity. •Most telegrams are sent at the onset of increased activity and not necessarily the peak of such activity.

Radio Behaviour

8 GHz 22 GHz

Observations at the two frequencies allow calculations of the spectral indices which, when used together with indices from other energy bands, e.g. gamma-ray, give the broadband Spectral Energy Distribution (SED) used to constrain models for emission.

Freq(GHz)

Epochyyyy-mm-dd

RMSmJy/beam

Speak

Jy/beamStotal

(Jy)Θmaj

(mas)

Θmin

(mas)

PA(o)

8.4 2007-11-10 0.37±0.40 4.85 5.10 2.2 0.7 12

8.4 2008-03-28 0.58± 0.11 3.38 4.24 2.8 0.6 -1

8.4 2008-08-08 0.39± 0.35 4.67 4.91 3.5 1.9 -3

22.3 2008-03-26 0.47± 0.99 3.12 3.43 1.9 1.2 -70

22.3 2008-03-08 0.47± 0.36 3.00 3.21 1.7 1.3 -72

D’Ammando et al., in preparation (general paper on PKS 0537-441)

Ojha et al., in preparation

Image Parameters

Skills gained and work done so far…

Scheduling VLBI experiments (MeerKAT will participate in VLBI experiments)

Calibrating VLBI data using AIPS (VLBA+ and LBA)

Imaging VLBI data using DIFMAP

Reducing gamma-ray data from the Fermi/LAT using Fermi science tools

Learning to make Spectral Index maps

Hungwe et al., submitted

D’Ammando et al., in preparation

Ojha et al., in preparation

Future work Fermi has been continuously collecting gamma-

ray light curves and spectra of all TANAMI sources using its main instrument, the Large Area Telescope

This will allow us to obtain broadband spectral indices of the cores and brightest jet features

From Fermi and TANAMI observations, we will also measure time delays between radio and gamma-ray emission bursts. These delays can be used to calculate how far from the core the gamma ray emission originate

Single dish monitoring of TANAMI sources with HartRAO

Thank You

References Abdo, A., et al. 2010, ApJS, 188, 405

Bastieri, D. 2009, The Astronomer's Telegram 2124

Heidt, J., Jager, K., Nilsson, K., Hopp, U., Fried, J. W., & Sutorius, E. 2003, A&A, 406, 565-577

Hungwe F., Ojha R., Kadler M., Booth R., Proceedings of the Workshop, Fermi meets Jansky, Bonn, 2010

Lucarelli, F., Striani, E., D'Ammando, F., et al., 2010, The Astronomer's Telegram 2454

Ojha, R, Kadler, M., et al. 2010, A &A, In Press, arXiv:1005.4432

Romero, G. E., Surpi, G. & Vucetich, H. 1995, A&A, 301, 641

Shepherd, M. C. 1997, Astronomical Society of the Pacific Conference Series, 125, 77

Tosti, G. 2008, The Astronomer's Telegram 1759

Treves, A., Belloni, T., Falomo, R., Fink, H., Maraschi, L., Sambruna, R. M., Tagliaferri, G. & Zimmermann, H. U. 1993 ApJ, 406, 447-450