We present the Allen Telescope Array Twenty-centimeter Survey ( ATATS ) , a multi-epoch ( 12 visits ) , 690 square degree 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 \sigma = 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 5 \sigma = 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 \sim 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 2 \sigma upper limit on the transient rate for such sources of 0.004 deg ^ { -2 } .
These results suggest that the \gtrsim 1 Jy transients reported by Matsumura et al .
( 32 ) may not be true transients , but rather variable sources at their flux density threshold .