Deep ATCA and VLA radio observations of short-GRB host galaxies. Constraints on star-formation rates, afterglow flux, and kilonova radio flares

TL;DR

This study conducted radio observations of short-GRB host galaxies to detect obscured star formation, afterglows, and kilonova radio flares, finding mostly non-detections that constrain star formation rates and flare luminosities, thus informing models of short-GRB progenitors.

Contribution

First comprehensive radio survey of short-GRB hosts that constrains star formation, afterglow luminosities, and kilonova radio flare predictions, with implications for progenitor models.

Findings

No new host with obscured star formation detected.

One host galaxy (GRB 100206A) shows starburst activity consistent with previous data.

Radio non-detections limit star formation rates and constrain magnetar-powered flare luminosities.

Abstract

We report the results of an extensive radio-continuum observing campaign of host galaxies of short gamma-ray bursts (GRBs). The goal of this survey was to search for optically obscured star formation, possibly indicative of a population of young short-GRB progenitors. Our sample comprises the hosts and host-galaxy candidates of 16 short-GRBs from 2005 to 2015, corresponding to roughly 1/3 of the presently known ensemble of well-localized short bursts. Eight GRB fields were observed with ATCA (at 5.5 and 9.0 GHz), and eight fields with the VLA (mostly at 5.5 GHz). The observations typically achieved a 1-sigma_rms of 5 to 8 microJy. In most cases they were performed years after the corresponding burst. No new short-GRB host with optically obscured star formation was found. Only one host galaxy was detected, the one of GRB 100206A at z=0.407. However, its starburst nature was already known from optical/IR data. Its measured radio flux can be interpreted as being due to a star formation rate (SFR) of about 60 M_sol/yr. This is in good agreement with earlier expectations based on the observed broad-band spectral energy distribution of this galaxy. The 15 non-detections constrain the SFRs of the suspected host galaxies and provide upper limits on late-time luminosities of the associated radio afterglows and predicted kilonova radio flares. The non-detection of radio emission from GRB explosion sites confirms the intrinsically low luminosity of short-GRB afterglows and places significant constraints on the parameter space of magnetar-powered radio flares. Luminous radio flares from fiducial massive magnetars have not been found.