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Published February 20, 2016 | Submitted + Published
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The Caltech-NRAO Stripe 82 Survey (CNSS) Paper. I. The Pilot Radio Transient Survey in 50 deg^2


We have commenced a multiyear program, the Caltech-NRAO Stripe 82 Survey (CNSS), to search for radio transients with the Jansky VLA in the Sloan Digital Sky Survey Stripe 82 region. The CNSS will deliver five epochs over the entire ~270 deg^2 of Stripe 82, an eventual deep combined map with an rms noise of ~40 μJy and catalogs at a frequency of 3 GHz, and having a spatial resolution of 3''. This first paper presents the results from an initial pilot survey of a 50 deg^2 region of Stripe 82, involving four epochs spanning logarithmic timescales between 1 week and 1.5 yr, with the combined map having a median rms noise of 35 μJy. This pilot survey enabled the development of the hardware and software for rapid data processing, as well as transient detection and follow-up, necessary for the full 270 deg^2 survey. Data editing, calibration, imaging, source extraction, cataloging, and transient identification were completed in a semi-automated fashion within 6 hr of completion of each epoch of observations, using dedicated computational hardware at the NRAO in Socorro and custom-developed data reduction and transient detection pipelines. Classification of variable and transient sources relied heavily on the wealth of multiwavelength legacy survey data in the Stripe 82 region, supplemented by repeated mapping of the region by the Palomar Transient Factory. A total of 3.9^(+0.5)_(-0.9)% of the few thousand detected point sources were found to vary by greater than 30%, consistent with similar studies at 1.4 and 5 GHz. Multiwavelength photometric data and light curves suggest that the variability is mostly due to shock-induced flaring in the jets of active galactic nuclei (AGNs). Although this was only a pilot survey, we detected two bona fide transients, associated with an RS CVn binary and a dKe star. Comparison with existing legacy survey data (FIRST, VLA-Stripe 82) revealed additional highly variable and transient sources on timescales between 5 and 20 yr, largely associated with renewed AGN activity. The rates of such AGNs possibly imply episodes of enhanced accretion and jet activity occurring once every ~40,000 yr in these galaxies. We compile the revised radio transient rates and make recommendations for future transient surveys and joint radio-optical experiments.

Additional Information

© 2016 The American Astronomical Society. Received 2015 April 29; accepted 2015 December 2; published 2016 February 11. The authors extend sincere thanks to Joan Wrobel and other scheduling staff at the NRAO in Socorro for extensive help with the scheduling of the VLA observations, and to James Robnett and other computing staff for their untiring assistance with the data storage and allocation of computing resources. The authors also wish to thank Luis Ho, Branimir Sesar, Eran Ofek, Sanjay Bhatnagar, Urvashi Rau, Kumar Golap, Vivek Dhawan, Craig Walker, Talvikki Hovatta, Tim Pearson, Anthony Readhead, Chuck Steidel, and Allison Strom for insightful discussions. The contribution of PTF collaboration members to optical data processing and optical follow-up observations relevant for this project is acknowledged. K.P.M. is grateful to NRAO for the Grote Reber Fellowship, and to Yamini Jangir for going over this manuscript and providing useful suggestions. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. S.R.K.'s research in part is supported by NASA and NSF. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California, Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research has made extensive use of ADS, CDS (Vizier and SIMBAD), NED, SDSS, and IRSA. We thank the anonymous referee for comments that helped in improving certain parts of the manuscript.

Attached Files

Published - Mooley_2016_ApJ_818_105.pdf

Submitted - 1601.01693.pdf


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