Abstract:
In some cases, the merger of two neutron stars can produce a rapidly rotating and highly magnetized millisecond magnetar. A
significant proportion of the rotational energy deposited to the emerging ejecta can produce a late-time radio brightening from
interacting with the ambient medium. Detection of thislate-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 legacy Giant Metrewave Radio Telescope (GMRT) at 1250, 610, and 325 MHz frequencies
and the upgraded-GMRT (uGMRT) at band 5 (1050–1450 MHz) and band 4 (550–900 MHz) after ∼2–11 yr 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 GRBs for any late-time low-frequency
emission. We find no evidence for such an emission. We find that none of these GRBs is consistent with maximally rotating
magnetar with a rotational energy of ∼ 1053 erg. 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 be able to detect these signatures or put more stringent
constraints on the model.
