Challenges for Fast Radio Bursts as Multi-Messenger Sources from Binary Neutron Star Mergers

Fast radio bursts (FRBs) are millisecond-duration transients from extragalactic sources, with their origins remaining a topic of active debate. Among the proposed progenitors, binary neutron star (BNS) mergers are compelling candidates for some non-repeating FRBs. However, associating FRBs with BNS mergers cannot be based solely on low chance coincidence probability. This study delineates necessary criteria for associating FRBs with BNS mergers, focusing on the post-merger ejecta environment. To underscore the significance of these criteria, we scrutinise the proposed association between GW190425 and FRB20190425A, considering the requirement for the FRB signal to traverse the dense merger ejecta without significant attenuation to remain detectable at 400 MHz. Our investigation reveals that if the FRB is linked to the gravitational wave event, the GW data support a highly off-axis configuration, with a probability of the BNS merger viewing angle p(θv > 30 degrees) being approximately 99.99%. This strongly excludes an on-axis system, which is required for this FRB to be detectable. We also find far-away FRB emission models inadequate to explain the FRB-GW connection. Thus, we conclude that GW190425 is not related to FRB20190425A. We discuss the implications for future multi-messenger observations, suggesting that BNS merger remnants are unlikely to account for more than 1% of FRB sources. This finding implies that short gamma-ray bursts should not be used to explain the global characteristics of the FRB host population.