Description:
<jats:title>Abstract</jats:title>
<jats:p>Fast radio bursts (FRBs) are short-lived (∼ms), energetic transients (having a peak flux density of ∼Jy) with no known prompt emission in other energy bands. We present results of a search for prompt X-ray emissions from 41 FRBs using the Cadmium Zinc Telluride Imager on <jats:italic>AstroSat</jats:italic>, which continuously monitors ∼70% of the sky. Our searches on various timescales in the 20–200 keV range, did not yield any counterparts in this hard X-ray band. We calculate upper limits on hard X-ray flux, in the same energy range and convert them to upper bounds for <jats:italic>η</jats:italic>: the ratio of X-ray to radio fluence of FRBs. We find <jats:italic>η</jats:italic> ≤ 10<jats:sup>8–10</jats:sup> for hard X-ray emission. Our results will help constrain the theoretical models of FRBs as the models become more quantitative and nearer, brighter FRBs are discovered.</jats:p>