Finding short GRB remnants in globular clusters: the VHE gamma-ray source in Terzan 5

TL;DR

This paper investigates whether the VHE gamma-ray source in Terzan 5 is a remnant of a short gamma-ray burst, analyzing signatures of relativistic outflows and ejecta to understand its origin and implications.

Contribution

It proposes that the VHE source in Terzan 5 could be a short GRB remnant, providing estimates of signatures and energies consistent with such an origin.

Findings

The VHE source's energy could be powered by a short GRB in a hadronic scenario.

The remnant's age estimate aligns with the occurrence of such events in the Galaxy.

Further observations could confirm the presence of relativistic shocks or heated plasma.

Abstract

Globular cluster are believed to boost the rate of compact binary mergers which may launch a certain type of cosmological gamma-ray bursts (GRBs). Therefore globular clusters appear to be potential sites to search for remnants of such GRBs. The very-high-energy (VHE) gamma-ray source HESS J1747-248 recently discovered in the direction of the Galactic globular cluster Terzan 5 is investigated for being a GRB remnant. Signatures created by the ultra-relativistic outflow, the sub-relativistic ejecta and the ionizing radiation of a short GRB are estimated for an expected age of such a remnant of t > 10^4 years. The kinetic energy of a short GRB could roughly be adequate to power the VHE source in a hadronic scenario. The age of the proposed remnant estimated from its extension possibly agrees with the occurrence of such events in the Galaxy. Sub-relativistic merger ejecta could shock-heat the ambient medium. Further VHE observations can probe the presence of a break towards lower energies expected for particle acceleration in ultra-relativistic shocks. Deep X-ray observations would have the potential to examine the presence of thermal plasma heated by the sub-relativistic ejecta. The identification of a GRB remnant in our own Galaxy may also help to explore the effect of such a highly energetic event on the Earth.