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VLBI Monitoring of Gamma-Ray Blazar PKS 0537-441

VLBI Monitoring of Gamma-Ray Blazar PKS 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.

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VLBI Monitoring of Gamma-Ray Blazar PKS 0537-441

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  1. VLBI Monitoring of Gamma-Ray Blazar PKS 0537-441 Faith Hungwe (Rhodes/HartRAO) Dr Roopesh Ojha (NASA/GSFC) Prof Roy Booth (HartRAO)

  2. Outline • Background • The TANAMI Program • Fermi • Results • Future Work

  3. 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: • 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 The Compton Gamma-Ray Observatory (time variability is a useful tool for linking behaviour at different wavelengths)

  4. 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

  5. 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

  6. The TANAMI Program Tracking AGN with Austral Milliarcsecond Interferometry TANAMI is the only parsec-scale monitoring program targeting AGN south of -30o

  7. 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.

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

  9. 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.

  10. 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).

  11. Gamma-Ray Light-curve Gamma-ray light curve for PKS 0537-441 spanning approximately 21 months from August 2008 to May 2010. All Fermi/LAT data shown here were downloaded from the public website http://fermi. gsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi. Fig 3: Gamma-ray light curve for PKS 0537-441 spanning approximately 21 months from August 2008 to May 2010. The square root of TS, the test statistic, gives a measure of the detection significance. Fig 3: Gamma-ray light curve for PKS 0537-441 spanning approximately 21 months from August 2008 to May 2010. The square root of TS, the test statistic, gives a measure of the detection significance.

  12. 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.

  13. Radio Behaviour 8 GHz 22 GHz

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

  15. 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

  16. 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

  17. Thank You

  18. 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

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