ASGARD: A Large Survey for Galactic Radio Transients

Peter Williams (Harvard-Smithsonian Center for Astrophysics)

ASGARD: A Large Survey for Galactic Radio Transients

Systematic studies of transient and variable radio emission are a relative novelty. Searches for slow radio transients, sources that vary over timescales of days to months, have so far tended to focus on extragalactic fields. Many Galactic sources, however, vary on these timescales, including X-ray binaries, cool dwarfs, and several objects of unknown nature discovered in previous efforts. ASGARD, the ATA Survey of Galactic Radio Dynamism, is an effort to characterize the population of Galactic radio transients and variables more fully. ASGARD has a large overall footprint (23 deg), a substantial number of epochs (200), and a significant dedication of observatory time (1700 hr over two years), which make it sensitive to rare objects as well as variability on many timescales. I will present early results from the analysis of two pointings: one centered on the microquasar Cygnus X-3 and one overlapping the Kepler field of view. Out of 134 sources detected in these pointings, the only compellingly variable one is Cygnus X-3, and no transients are detected. I estimate number counts for potential Galactic radio transients and compare our current limits to previous work and our projection for the fully analyzed ASGARD data set.

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