Nov 07, 2012

Steve Croft, University of California: Berkeley

"AGN Variability, Tidal Disruptions, and Transients from Next Generation Radio Telescopes"

The next generation of radio telescopes such as the Australian Square Kilometer Array Pathfinder (ASKAP) will provide radio variability information with a cadence of days for samples of hundreds of thousands of active galactic nuclei (AGNs). They will also potentially detect tens to hundreds of transient events per month, including radio afterglows from stellar explosions such as supernovae and gamma ray bursts; but the majority of these radio transients may arise from the tidal disruption of stars passing close to supermassive black holes. An early pioneer in the new generation of radio telescopes is the Allen Telescope Array (ATA), which undertook several systematic searches for radio transients and variability. I will present results from the Pi GHz Sky Survey (PiGSS), a survey which includes a wide field (~5000 sq. deg.) component, and also a total of 459 repeated observations of four 12 sq. deg. deep fields. PiGSS provides some of the most sensitive current upper limits on the transient rate in the radio, reaching sensitivities of a few milliJanskies over effective areas of thousands of square degrees. PiGSS also discovered several strongly variable sources, and provides variability measurements for hundreds of radio AGNs, for hundreds of epochs with a cadence of days.

Steve is an Assistant Project Astronomer working with Geoff Bower in Berkeley and David Kaplan in Milwaukee on large radio surveys, transients, and variable sources. He helped commission the Allen Telescope Array for science operations and developed data analysis pipelines. He got his PhD from the University of Oxford, working with Steve Rawlings on radio galaxies in cluster environments. He then worked as a postdoc at the Lawrence Livermore National Laboratory with Wil van Breugel and Bob Becker, studying radio galaxy hosts and environments, high-redshift protoclusters, and jet-induced star formation, using data at a wide range of wavelengths from many different telescopes.