A VLA search for 5 GHz radio transients and variables at low Galactic latitudes

TL;DR

This study used the VLA to search for short-lived 5 GHz radio transients and variability at low Galactic latitudes, finding a low transient density and significant variability likely due to scintillation.

Contribution

First comprehensive 5 GHz transient survey at low Galactic latitudes with real-time detection and multi-wavelength follow-up, providing new transient density estimates and variability analysis.

Findings

Detected a single transient with 2.4 mJy flux density.

Estimated transient sky surface density of 0.039 deg^-2 for >1.8 mJy.

Found >30% of sources brighter than 1.8 mJy are variable at >4 sigma.

Abstract

We present the results of a 5 GHz survey with the Very Large Array, designed to search for short-lived (<1 day) transients and to characterize the variability of radio sources at milli-Jansky levels. A total sky area of 2.66 deg^2, spread over 141 fields at low Galactic latitudes was observed 16 times with a cadence sampling timescales of days, months and years. Most of the data were searched for transients in near real time. Candidates were followed up using visible light telescopes (1-2 hr delays) and the X-Ray Telescope on board the Swift satellite. The final processing of the data revealed a single possible transient with a flux density of 2.4 mJy. This implies a transients, >1.8 mJy, sky surface density of 0.039 (-0.032/+0.13) deg^-2. This areal density is consistent with the sky surface density of transients from the Bower et al. survey extrapolated to 1.8 mJy. Our observed transient areal density is consistent with a Neutron Stars (NSs) origin for these events. Furthermore, we use the data to measure the sources variability on days to years time scales, and we present the variability structure function of 5 GHz sources. The mean structure function shows a fast increase on ~1 day time scale, followed by a slower increase on time scales of up to 10 days. On time scales between 10-60 days the structure function is roughly constant. We find that >30% of the unresolved sources brighter than 1.8 mJy are variable at the >4 sigma confidence level, presumably due mainly to refractive scintillation.