Search for merger ejecta emission from late time radio observations of short GRBs using GMRT

TL;DR

This study conducted late-time low-frequency radio observations of five short GRBs using GMRT to search for merger ejecta emission indicative of magnetar remnants, but found no evidence, thus constraining the energy of potential magnetars.

Contribution

First delayed low-frequency radio observations of short GRBs targeting merger ejecta emission, providing constraints on magnetar energies post-merger.

Findings

No detection of late-time radio emission from the five GRBs.

Constraints on the rotational energy of magnetars, excluding maximally rotating ones.

Highlights the need for future radio observatories to detect or further constrain such emissions.

Abstract

Short gamma-ray bursts (GRBs) are the aftermath of compact binary mergers involving neutron stars. If the merger remnant is a millisecond magnetar instead of a black hole, a significant proportion of the rotational energy deposited to the emerging ejecta can produce a late-time radio brightening from its interaction with the ambient medium. Detection of this late-time radio emission from short GRBs can have profound implications for understanding the physics of the progenitor. We report the radio observations of five short GRBs - 050709, 061210, 100625A, 140903A, and 160821B using the Giant Metrewave Radio Telescope (GMRT) at 1250, 610, and 325 MHz frequencies after $\sim$ $2 - 11$ years from the time of the burst. The GMRT observations at low frequencies are particularly important to detect the signature of merger ejecta emission at the peak. These observations are the most delayed searches associated with some of these GRBs for any late-time low-frequency emission. We find no evidence for such an emission. We find that none of these GRBs are consistent with maximally rotating magnetar with a rotational energy of $\sim 10^{53}\, {\rm ergs}$. However, magnetars with lower rotational energies cannot be completely ruled out. Despite the non detection, our study underscores the power of radio observations in the search for magnetar signatures associated with short GRBs. However, only future radio observatories may have the capabilities to either detect these signatures or put more stringent constraints on the model.