TANAMI: tracking active galactic nuclei with austral milliarcsecond interferometry

Abstract

Context. A number of theoretical models vie to explain the γ-ray emission from active galactic nuclei (AGN). This was a key discovery of EGRET. With its broader energy coverage, higher resolution, wider field of view and greater sensitivity, the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope is dramatically increasing our knowledge of AGN γ-ray emission. However, discriminating between competing theoretical models requires quasi-simultaneous observations across the electromagnetic spectrum. By resolving the powerful parsecscale relativistic outflows in extragalactic jets and thereby allowing us to measure critical physical properties, Very Long Baseline Interferometry observations are crucial to understanding the physics of extragalactic γ-ray objects. Results. We present first epoch images for 43 sources, some observed for the first time at milliarcsecond resolution. Parameters of these images as well as physical parameters derived from them are also presented and discussed. These and subsequent images from the TANAMI survey are available at http://pulsar.sternwarte.uni-erlangen.de/tanami/. Conclusions. We obtain reliable, high dynamic range images of the southern hemisphere AGN. All the quasars and BL Lac objects in the sample have a single-sided radio morphology. Galaxies are either double-sided, single-sided or irregular. About 28% of the TANAMI sample has been detected by LAT during its first three months of operations. Initial analysis suggests that when galaxies are excluded, sources detected by LAT have larger opening angles than those not detected by LAT. Brightness temperatures of LAT detections and non-detections seem to have similar distributions. The redshift distributions of the TANAMI sample and sub-samples are similar to those seen for the bright γ-ray AGN seen by LAT and EGRET but none of the sources with a redshift above 1.8 have been detected by LAT.

Unusual flaring activity in the blazar PKS 1424−418 during 2008−2011

“…2; observed on 2008 March 26) clearly indicates that this source is extremely core dominated at this frequency. This is further confirmed by the 8.4 GHz image in Ojha et al (2010) which shows a dominant, compact VLBI core and a very diffuse and resolved jet. The milliarcsecond core flux densities of PKS 1424−418 at 8.4 GHz at four epochs during 2008 through 2010 are listed in Table 2.…”

“…High resolution Very Long Baseline Interferometry (VLBI) observations of this blazar carried out as part of the TANAMI program show it to have a faint low-surface-brightness jet with a wide opening angle (Ojha et al 2010). At the milliarcsecond scale, the 22.3 GHz image of PKS 1424−418 ( Fig.…”

“…These flux A40, page 4 of 11 densities were obtained by model fitting a circular Gaussian to the core of VLBI images made by the TANAMI program. For details on the observations, imaging and model fitting process refer to Ojha et al (2010).…”

“…With mean flux densities over 3 Jy and known variability at multiple radio frequencies (Tingay et al 2003), PKS 1424−418 is a strong and variable radio source. High resolution Very Long Baseline Interferometry (VLBI) observations of this blazar are being carried out as part of the TANAMI program (Ojha et al 2010), and radio monitoring is being done as part of the F-GAMMA project (Fuhrmann et al 2007;Angelakis et al 2008), the Submillimeter Array (SMA, Gurwell et al 2007), and other radio telescopes. 5.…”

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

“…This is the second in a series of papers presenting results from broadband observations of PKS 2004−447. The observations reported in this series were conducted as part of the TANAMI 2 multiwavelength programme (Ojha et al 2010;Kadler et al 2015) that monitors γ-ray loud AGNs south of −30 • declination. In a separate paper (Kreikenbohm et al 2016, hereafter Paper I), we discussed X-ray observations with XMM-Newton and Swift, finding a flat blazar-like power law and moderate variability on time scales down to months with an observed luminosity of (0.7-2.6) ×10 44 erg/s.…”