Are there radio-loud and radio-quiet gamma-ray bursts?

Abstract

ABSTRACT The potential existence of two separate classes of Long-duration Gamma-Ray Bursts (LGRBs) with and without radio afterglow emission, corresponding to radio-bright/loud and radio-dark/quiet populations, has been recently argued and favoured in the GRB literature. The radio-quiet LGRBs have been found to have, on average, lower total isotropic gamma-ray emissions (Eiso) and shorter intrinsic prompt gamma-ray durations (e.g. T90z). In addition, a redshift −T90z anticorrelation has been discovered among the radio-loud LGRBs, which is reportedly missing in the radio-quiet class. Here, we discuss the significance of the differences between the energetics and temporal properties of the two proposed classes of radio-loud and radio-quiet LGRBs. We show that much of the proposed evidence in support of the two distinct radio populations of LGRBs can be explained away in terms of selection effects and sample incompleteness. Our arguments are based on the recent discovery of the relatively strong, highly significant positive correlation between the total isotropic emission (Eiso) and the intrinsic prompt duration (T90z) that is present in both populations of short-hard and long-soft GRBs, predicted, quantified, and reported for the first time by Shahmoradi (2013a;2013b) and Shahmoradi & Nemiroff (2015).