Searching for the radio remnants of short duration gamma-ray bursts

TL;DR

This study uses late-time radio observations of short gamma-ray bursts to search for radio remnants from neutron star mergers, constraining ejecta properties and ruling out highly energetic ejecta and magnetar remnants in most cases.

Contribution

It provides new constraints on the ejecta mass and energy from neutron star mergers using radio observations, and tests the magnetar remnant hypothesis.

Findings

Very energetic ejecta (E_ej > 5*10^{52} erg) are ruled out for ejecta mass M_ej < 0.01 M_sun.

The presence of a powerful magnetar remnant is excluded in these events.

Early radio emission in GRB 170817A may be suppressed by jet effects.

Abstract

Neutron star mergers produce a substantial amount of fast-moving ejecta, expanding outwardly for years after the merger. The interaction of these ejecta with the surrounding medium may produce a weak isotropic radio remnant, detectable in relatively nearby events. We use late-time radio observations of short duration gamma-ray bursts (sGRBs) to constrain this model. Two samples of events were studied: four sGRBs that are possibly in the local (<200 Mpc) universe were selected to constrain the remnant non-thermal emission from the sub-relativistic ejecta, whereas 17 sGRBs at cosmological distances were used to constrain the presence of a proto-magnetar central engine, possibly re-energezing the merger ejecta. We consider the case of GRB~170817A/GW170817, and find that in this case the early radio emission may be quenched by the jet blast-wave. In all cases, for ejecta mass range of M_ej \lesssim 10^{-2} (5 * 10^{-2}) M_sun, we can rule out very energetic merger ejecta E_ej \gtrsim 5 * 10^{52}(10^{53}) erg, thus excluding the presence of a powerful magnetar as a merger remnant.