The Allen telescope array PiGHz sky survey II. daily and monthly monitoring for transients and variability in the Boötes field

Abstract

We present results from daily radio continuum observations of the Boötes field as part of the PiGHz Sky Survey (PiGSS). These results are part of a systematic and unbiased campaign to characterize variable and transient sources in the radio sky. The observations include 78 individual epochs distributed over five months at a radio frequency of 3.1GHz with a median rms image noise in each epoch of 2.8mJy. We produce five monthly images with a median rms of 0.6mJy. No transient radio sources are detected in the daily or monthly images. At 15mJy, we set an upper limit (2σ) to the surface density of one-day radio transients at 0.025 deg-2. At 5mJy, we set an upper limit (2σ) to the surface density of one-month radio transients at 0.18 deg-2. We also produce light curves for 425 sources and explore the variability properties of these sources. Approximately 20% of the sources exhibit some variability on daily and monthly timescales. The maximum rms fractional modulations on the one-day and one-month timescales for sources brighter than 10mJy are 2 and 0.5, respectively. The probability of a daily fluctuation for all sources and all epochs by a factor of 10 is less than 10-4. We compare the radio to mid-infrared variability for sources in the field and find no correlation. Finally, we apply the statistics of transient and variable populations to constrain models for a variety of source classes. © 2011 The American Astronomical Society. All rights reserved.