Extragalactic Transients in the Era of Wide-Field Radio Surveys. I. Detection Rates and Light Curve Characteristics

The impending era of wide-field radio surveys has the potential to revolutionize our understanding of astrophysical transients. Here we evaluate the prospects of a wide range of planned and hypothetical radio surveys using the properties and volumetric rates of known and hypothetical classes of extragalactic synchrotron radio transients (e.g., onand off-axis gamma-ray bursts, supernovae, tidal disruption events, compact object mergers). Utilizing these sources and physically motivated considerations we assess the allowed phase-space of radio luminosity and peak timescale for extragalactic transients. We also include for the first time effects such as redshift evolution of the rates, K-corrections, and non-Euclidean luminosity distance, which affect the detection rates of the most sensitive surveys. The number of detected events is calculated by means of a Monte Carlo method, using the various survey properties (depth, cadence, area) and realistic detection criteria that include a cut on the minimum variability of the transients during the survey and an assessment of host galaxy contamination. For the detected events we also quantify how well each light curve is characterized (e.g., the fraction of sources with a measured rise time, decline time, and peak brightness). We find that near-term GHz frequency surveys (ASKAP/VAST, Very Large Array Sky Survey) will detect few events: . 30− 50 onand off-axis long GRBs and off-axis tidal disruption events, and ∼ 10− 20 neutron star binary mergers if ∼ 1% of the mergers result in a stable millisecond magnetar. Lowfrequency surveys (e.g., LOFAR) are unlikely to detect any transients, while a hypothetical large-scale mm survey may detect ∼ 40 on-axis long GRBs. On the other hand, we find that SKA surveys at ∼ 0.1 − 1 GHz have the potential to uncover thousands of transients, mainly onand off-axis long GRBs, on-axis short GRBs, off-axis TDEs, and neutron star binary mergers with magnetar remnants. Subject headings: gamma-ray bursts: general — radio continuum: general — supernovae: general — surveys