Letter to the Editor

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

Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
e-mail: wilfried.domainko@mpi-hd.mpg.de

Received: 22 June 2011
Accepted: 4 August 2011

Abstract

Context. Globular cluster are believed to boost the rate of compact binary mergers that may launch a certain type of cosmological gamma-ray burst (GRB). Therefore globular clusters appear to be potential sites to search for remnants of such GRBs.

Aims. 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.

Methods. Signatures created by the ultrarelativistic outflow, the subrelativistic ejecta and the ionizing radiation of a short GRB are estimated for an expected age of such a remnant of t ≳ 10⁴ years.

Results. The kinetic energy of a short GRB could roughly be adequate for powering 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. Subrelativistic merger ejecta could shock-heat the ambient medium.

Conclusions. Further VHE observations can probe for the presence of a break towards lower energies expected for particle acceleration in ultrarelativistic shocks. Deep X-ray observations would have the potential to examine whether there is any thermal plasma heated by the subrelativistic 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.