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30th of April 2015
A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz
by Martin Bell (CASS)
We have just finished a survey that targets an extremely deep part of the time-domain radio sky with the Australia Telescope Compact Array (ATCA). We chose the Chandra Deep Field South (CDFS) as the region for our survey. The CDFS is a 0.3 deg2 region favored for its low optical and HI extinction. A plethora of multi-wavelength data from both space and ground based facilities are available for this region. In late 2009, Huynh et al. (2012) obtained observations of the CDFS at 5.5 GHz (144 hours) which resulted in a map of ~10 micro-Janskys noise. The goal of our survey was simple; to obtain a further two epochs of observations (100 hours) of the CDFS that were designed to match those of Huynh et al. (2012). The motivation for this survey was to search a bespoke region of parameter space (5 GHz and <1 mJy) for signatures of dynamic radio emission on long timescales: months to years. We found four variable radio sources out of total 124 sources within the field. One of the sources showed variations greater than 50%. Nearly all of the sources within the field were cross-matched with AGN or QSOs. The remarkable thing about the detections was that they were all inverted spectrum radio sources. We had complete spectral information, including optical and X-ray IDs, of the objects. Our conclusions are that these variable objects are young GPS sources whereby the variability and spectra are indicative of fairly recent activity within the radio jets. The spectra of these variable sources have implications for future blind radio surveys, due to the inverted spectra they will be more difficult to detect e.g. at 1.4 GHz with ASKAP. See our paper on astro-ph/1504.06371 (Bell, Huynh, Hancock, Murphy, Gaensler, Burlon, Trott, and Bannister 2015, MNRAS, accepted) for further details.

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