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 website gsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi. 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) Θ maj (mas) Θ min (mas) PA ( o ) ± ± ± ± ± D’Ammando 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  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

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