Search

Short gamma-ray bursts (GRBs) are explosive transients caused by binary mergers of compact objects containing at least one neutron star. Multiwavelength afterglow observations provide constraints on the physical parameters of the jet, its surrounding medium, and the microphysics of the enhanced magnetic fields and accelerated electrons in the blast wave at the front of the jet. The synchrotron radio emission can be tracked for much longer than in other spectral regimes, and it can pin down the evolution of the spectral peak. We present the results of a systematic observing campaign of eight short GRBs with the MeerKAT radio telescope. Additionally, we present observations of four of these short GRBs using the ATCA radio telescope and two of these short GRBs with the e -MERLIN radio telescope. Using these results we report one possible detection of a short GRB afterglow from GRB 230217A and deep upper limits for the rest of our short GRB observations. We use these observations to place constraints on some of the physical parameters, in particular those related to electron acceleration, the circumburst density, and gamma-ray energy efficiency. We discuss how deeper observations with new and upgraded telescopes should be able to determine if the gamma-ray efficiency differs between long and short GRBs. We also report detections of the likely host galaxies for four of the eight GRBs and upper limits for another GRB, increasing the number of detected host galaxies in the radio with implications for the star formation rate in these galaxies. [ABSTRACT FROM AUTHOR]

A new generation of radio telescopes with excellent sensitivity, instantaneous uv coverage, and large fields of view, are providing unprecedented opportunities for performing commensal transient searches. Here, we present such a commensal search in deep observations of short gamma-ray burst fields carried out with the MeerKAT radio telescope in South Africa at 1.3 GHz. These four hour observations of eight different fields span survey lengths of weeks to months. We also carry out transient searches in time slices of the full observations, at time-scales of 15 min and 8 s. We find 122 variable sources on the long time-scales, of which 52 are likely active galactic nuclei, but there are likely also some radio flaring stars. While the variability is intrinsic in at least two cases, most of it is consistent with interstellar scintillation. In this study, we also place constraints on transient rates based on state-of-the-art transient simulations codes. We place an upper limit of 2 × 10−4 transients per day per square degree for transients with peak flux of 5 mJy, and an upper limit of 2.5 × 10−2 transients per day per square degree for transients with a fluence of 10 Jy ms, the minimum detectable fluence of our survey. [ABSTRACT FROM AUTHOR]