VLBI Monitoring of Gamma-Ray Blazar PKS 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 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 J The TANAMI Program Tracking AGN with Austral Milliarcsecond Interferometry TANAMI is the only parsec-scale monitoring program targeting AGN south of -30 o 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 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 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 websitegsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi.http://fermi Fig 3: Gamma-ray light curve for PKS spanning approximately 21 months from August 2008 to May The square root of TS, the test statistic, gives a measure of the detection significance. Gamma-ray light curve for PKS spanning approximately 21 months from August 2008 to May 2010. PKS 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 GHz22 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) Epoch yyyy-mm-dd RMS mJy/beam S peak Jy/beam S total (Jy) maj (mas) min (mas) PA ( o ) DAmmando et al., in preparation (general paper on PKS ) 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 DAmmando 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, 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: 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 ApJ, 406,