A Search for Low-frequency Radio Pulses from Long Gamma-Ray Bursts with the Murchison Widefield Array

It has been proposed that coherent radio emission could be emitted during or shortly following a gamma-ray burst (GRB). Here we present a low-frequency (170-200 MHz) search for radio pulses associated with long-duration GRBs using the Murchison Widefield Array (MWA). The MWA, with its rapid-response system, is capable of performing GRB follow-up observations within approximately 30 s. Our single pulse search, with temporal and spectral resolutions of 100 μs and 10 kHz, covers dispersion measures up to 5000 pc cm⁻³. Two single pulse candidates are identified with significance greater than 6σ, surviving a friends-of-friends analysis. We rule out random fluctuations as their origin at a confidence level of 97% (2.2σ). We caution that radio frequency interference from digital TV (DTV) is most likely the origin of these pulses since the DTV frequency bands almost cover the entire observing frequency band. If they are astrophysical signals, we estimate the peak flux densities for our pulse candidates of 3.6 ± 0.6 and 10.5 ± 1.5 Jy, with corresponding fluences of 431 ± 74 and 211 ± 37 Jy ms, respectively. Based on these observations and the assumption of a magnetar origin for the pulse, we constrain the radio emission efficiency as ϵ_r ∼ 10⁻³ for both candidates, which is consistent with pulsar observations. Our results highlight the promising potential of new-generation radio telescopes such as the MWA to probe the central engines of GRBs.