Finding LoTSS of hosts for GRBs: a search for galaxy–gamma-ray burst coincidences at low frequencies with LOFAR

Abstract

ABSTRACT The LOFAR (Low Frequency Array) Two-metre Sky Survey (LoTSS) is an invaluable new tool for investigating the properties of sources at low frequencies and has helped to open up the study of galaxy populations in this regime. In this work, we perform a search for host galaxies of gamma-ray bursts (GRBs). We use the relative density of sources in Data Release 2 (DR2) of LoTSS to define the probability of a chance alignment, Pchance, and find 18 sources corresponding to 17 GRBs that meet a Pchance < 1 per cent criterion. We examine the nature and properties of these radio sources using both LOFAR data and broad-band information, including their radio spectral index, star formation rate estimates, and any contributions from active galactic nucleus emission. Assuming that the radio emission is dominated by star formation, we find that our sources show high star formation rates (101–103 M⊙ yr−1) compared with both a field galaxy sample and a sample of core-collapse supernova hosts, and the majority of putative hosts are consistent with ultra-luminous infrared galaxy classifications. As a result of our analyses, we define a final sample of eight likely GRB host candidates in the LoTSS DR2 survey.