Abstract
Abstract Discovered in 2011 with LOFAR, the 15 Jy low-frequency radio transient ILT J225347+862146 heralds a potentially prolific population of radio transients at <100 MHz. However, subsequent transient searches in similar parameter space yielded no detections. We test the hypothesis that these surveys at comparable sensitivity have missed the population due to mismatched survey parameters. In particular, the LOFAR survey used only 195 kHz of bandwidth at 60 MHz, while other surveys were at higher frequencies or had wider bandwidth. Using 137 hr of all-sky images from the Owens Valley Radio Observatory Long Wavelength Array, we conduct a narrowband transient search at ∼10 Jy sensitivity with timescales from 10 minutes to 1 day and a bandwidth of 722 kHz at 60 MHz. To model the remaining survey selection effects, we introduce a flexible Bayesian approach for inferring transient rates. We do not detect any transient and find compelling evidence that our nondetection is inconsistent with the detection of ILT J225347+862146. Under the assumption that the transient is astrophysical, we propose two hypotheses that may explain our nondetection. First, the transient population associated with ILT J225347+862146 may have a low all-sky density and display strong temporal clustering. Second, ILT J225347+862146 may be an extreme instance of the fluence distribution, of which we revise the surface density estimate at 15 Jy to 1.1 × 10−7 deg−2 with a 95% credible interval of (3.5 × 10−12, 3.4 × 10−7) deg−2. Finally, we find a previously identified object coincident with ILT J225347+862146 to be an M dwarf at 420 pc.
Highlights
IntroductionA new generation of low radio frequency (ν 300 MHz; wavelength λ 1 m) interferometer arrays based on dipoles have emerged
Over the last decade, a new generation of low radio frequency (ν 300 MHz; wavelength λ 1 m) interferometer arrays based on dipoles have emerged
Unlike Anderson et al (2019), which searched for broadband (∆ν/ν > 1) counterparts to ILT J225347+862146, we explore the possibility that the event was narrowband, with ∆ν/ν 1
Summary
A new generation of low radio frequency (ν 300 MHz; wavelength λ 1 m) interferometer arrays based on dipoles have emerged. Dipole arrays simultaneously offer a large effective area (∼ λ2/4π) as well as field of view (FOV) and are well suited to synoptic surveys of the time domain sky. Some coherent emission mechanisms prefer low radio frequencies (e.g. electron cyclotron maser emission, Treumann 2006) or have steep spectra (e.g. pulsars, Jankowski et al 2018). Despite their potential prevalence at low radio frequencies, the luminosity function for coherent emission sources at low radio frequencies remains poorly characterized. Initial transient surveys probing timescales of seconds to years at these frequencies have made significant progress into the transient rate-flux density phase space, but the transient populations at these frequencies remain poorly understood compared to higher radio frequencies
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