Radio Afterglows and Host Galaxies of Gamma-Ray Bursts

TL;DR

This study examines how host galaxy radio emissions influence GRB afterglow observations, revealing a frequency-dependent correlation that aids in estimating host brightness and assessing detectability with FAST.

Contribution

It introduces a statistical correlation between host galaxy radio flux ratios and frequency, improving estimates of host contributions and evaluating GRB detectability with FAST.

Findings

Host contribution increases at lower frequencies.

Most high-luminosity GRBs are detectable by FAST at z=1.

Many low-luminosity GRBs near Earth are detectable despite weaker afterglows.

Abstract

Considering the contribution of the emission from the host galaxies of gamma-ray bursts (GRBs) to the radio afterglows, we investigate the effect of host galaxies on observations statistically. For the three types of events, e.g. low-luminosity, standard and high-luminosity GRBs, it is found that a tight correlation exists between the ratio of the radio flux (RRF) of host galaxy to the total radio peak emission and the observational frequency. Especially, toward lower frequencies, the contribution from the host increases significantly. The correlation can be used to get a useful estimate for the radio brightness of those host galaxies which only have very limited radio afterglow data. Using this prediction, we re-considered the theoretical radio afterglow light curves for four kinds of events, i.e. high-luminosity, low-luminosity, standard and failed GRBs, taking into account the contribution from the host galaxies and aiming at exploring the detectability of these events by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Lying at a typical redshift of $z=1$, most of the events can be detected by FAST easily. For the less fierce low-luminosity GRBs, their radio afterglows are not strong enough to exceed the sensitivity limit of FAST at such distances. However, since a large number of low luminosity bursts actually happen very near to us, it is expected that FAST will still be able to detect many of them.