THE ALLEN TELESCOPE ARRAY TWENTY-CENTIMETER SURVEY—A 690 DEG², 12 EPOCH RADIO DATA SET. I. CATALOG AND LONG-DURATION TRANSIENT STATISTICS

Abstract

We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch (12 visits), 690 deg 2 radio image and catalog at 1.4 GHz. The survey is designed to detect rare, very bright transients as well as to verify the capabilities of the ATA to form large mosaics. The combined image using data from all 12 ATATS epochs has rms noise σ = 3.94 mJy beam −1 and dynamic range 180, with a circular beam of 150 FWHM. It contains 4408 sources to a limiting sensitivity of 5σ = 20 mJy beam −1 . We compare the catalog generated from this 12 epoch combined image to the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency, and find that we can measure source positions to better than ∼20 . For sources above the ATATS completeness limit, the median flux density is 97% of the median value for matched NVSS sources, indicative of an accurate overall flux calibration. We examine the effects of source confusion due to the effects of differing resolution between ATATS and NVSS on our ability to compare flux densities. We detect no transients at flux densities greater than 40 mJy in comparison with NVSS and place a 2σ upper limit of 0.004 deg −2 on the transient rate for such sources. These results suggest that the 1 Jy transients reported by Matsumara et al. may not be true transients, but rather variable sources at their flux density threshold.

Unveiling the population of orphanγ-ray bursts

“…Despite specific studies designed to search for OAs in X-ray surveys (Grindlay 1999;Greiner et al 2000), in optical surveys (Vreeswijk 2002;Rau et al 2006;Malacrino et al 2007;Rau et al 2007), and in the radio band (Levinson et al 2002;Gal-Yam et al 2006;Bannister et al 2011;Bell et al 2011;Bower & Saul 2011;Croft et al 2010;Frail et al 2012;Carilli et al 2003;Matsumura et al 2009;Lazio et al 2010), no OA have been conclusively detected so far.…”

The Allen Telescope Array Twenty-Centimeter Survey—a 700-Square-Degree, Multi-Epoch Radio Data Set. Ii. Individual Epoch Transient Statistics

“…In Croft et al (2010), hereafter Paper I, we introduced a 12-epoch survey undertaken with the Allen Telescope Array (ATA; Welch et al 2009), the ATA Twenty-centimeter Survey (ATATS), and compared the image and catalog made with data from all 12 epochs to the NRAO VLA Sky Survey (NVSS; Condon et al 1998), a survey also at 1.4 GHz (with 45 resolution, compared to the 150 resolution of our data) undertaken with the VLA between 1993 and 1997. Unfortunately, both the raw and reduced data for epoch ATA4 were subsequently lost due to two disk failures, so for this paper we created a new image and catalog made with data from the remaining 11 epochs (which we term the master mosaic and master catalog).…”

VAST: An ASKAP Survey for Variables and Slow Transients

“…The sources were detected in a drift scan mode and have flux densities greater than 1 Jy, with typical timescales of minutes to days. (Note, however, the questions raised about these results by Croft et al 2010Croft et al , 2011, and the discussion about the resulting transient event rates by Ofek et al 2011. ) As briefly discussed earlier in Section 3.1, Bower et al (2007) reported the detection of 10 transient radio sources in archival VLA data at 4.8 and 8.4 GHz.…”