Modeling Supernova-like Explosions Associated with Gamma-ray Bursts with Short Durations

TL;DR

This paper explores the possibility of supernova-like ejecta, called macronovae, associated with short gamma-ray bursts, powered by radioactive decay, and assesses their observability with current telescopes.

Contribution

It introduces the concept of macronovae in short GRBs and analyzes their potential detectability using existing observational capabilities.

Findings

Macronovae could be powered by neutron decay or Nickel radioactive decay.

Observations within one hour to one day post-burst can constrain macronova parameters.

Short GRBs may have faint supernova-like components, detectable with current telescopes.

Abstract

There is now good evidence linking short-hard GRBs with both elliptical and spiral galaxies at relatively low redshifts, redshift of about 0.2. This contrasts with the average redshift of about 2 of long-duration events, which also occur only in star-forming galaxies. The diversity of hosts is reminiscent of type Ia supernovae, which are widely (but not universally) believed to originate from the coalescence of white dwarfs. By analogy, it has been postulated that short-hard bursts originate from neutron star mergers. Mergers, as well as stellar core-collapse events (type II SNe and long-duration GRBs) are accompanied by long-lived sub-relativistic components powered by radioactive decay of unstable elements produced in the explosion. It is therefore interesting to explore whether short duration events also have ejecta powered by radioactivity (i.e. that are supernova-like). Observations already inform us that any supernova like component in the first few well studied short hard bursts must be fainter than those typical of type Ia or core-collapse supernovae. Rather than refer to weaker supernova-like component as ``mini-super nova'', an etymologically indefensible term, I use the term {\it macronova}. I investigate the observability of macronovae powered by neutron decay and by radioactive Nickel. Separately, I note that a macronova will reprocess energetic emission arising from a long lived central source. I find that surprisingly interesting limits on the basic parameters of macronovae can be obtained provided observations are obtained with current 10-m class telescopes over a range of one hour to one day following the burst.