A Revised View of the Transient Radio Sky

Abstract

We report on a re-analysis of archival data from the Very Large Array for a sample of 10 long-duration radio transients reported by Bower and others. These transients have an implied all-sky rate that would make them the most common radio transient in the sky and yet most have no quiescent counterparts at other wavelengths and therefore no known progenitor (other than Galactic neutron stars). We find that more than half of these transients are due to rare data artifacts. The remaining sources have lower signal-to-noise ratio (S/N) than initially reported by 1σ -1.5σ . This lowering of S/N matters greatly since the sources are at the threshold. We are unable to decisively account for the S/N differences. By two orthogonal criteria one source appears to be a good detection. Thus the rate of long-duration radio transients without optical counterparts is, at best, comparable to that of the class of recently discovered Swift J1644+57 nuclear radio transients. We revisit the known and expected classes of long-duration radio transients and conclude that the dynamic radio sky remains a rich area for further exploration. Informed by the experience of past searches for radio transients, we suggest that future surveys pay closer attention to rare data errors and ensure that a wealth of sensitive multi-wavelength data be available in advance of the radio observations and that the radio searches should have assured follow-up resources.

Discovery of a Meter-Wavelength Radio Transient in the Swire Deep Field: 1046+59

“…Our detection indicates a transient surface density that is more strict than the limit from Bower et al (2007), even considering the factor of two decrease suggested by Frail et al (2011). However, the frequency range in Figure 9 sults with similar flux sensitivity.…”

“…All published limits have been scaled to represent the surface density at 95% confidence. The Bower et al (2007) results have also been adjusted to reflect the recent reanalysis by Frail et al (2011). For completeness, we note the non-detection limit from Lazio et al (2010) of Σ < 10 −7 with flux sensitivity >2.5 kJy at 74 MHz.…”

Radio Counterparts of Compact Binary Mergers Detectable in Gravitational Waves: A Simulation for an Optimized Survey

“…In fact, radio afterglows have been already detected for four sGRBs(e.g., Fong et al 2015) and they will be detectable counterparts of GW merger events (Feng et al 2014). Recent observations suggest that the radio transient sky is far quieter compared to the optical one, so we expect far fewer false positives by a factor of a hundred or more depending on the sky location than in the optical-IR (e.g., Frail et al 2012;Mooley et al 2013Mooley et al , 2016. This paper focuses on strategies for detecting and identifying, following the detection of a GW event, two different radio post-merger counterparts: (i) the longer duration radio remnants that may last from months to years and (ii) the faster ultrarelativistic radio afterglow components that last weeks to months (Nakar & Piran 2011;Piran et al 2013;Margalit & Piran 2015).…”

MILLIMETER TRANSIENT POINT SOURCES IN THE SPTpol 100 SQUARE DEGREE SURVEY

“…No single map contributes more than this, which implies that no single observation dominates the observed excess. This rules out the kinds of brief instrumental systematics identified by Frail et al (2012) in previous radio transient surveys.…”