Constraining the Environmental Properties of FRB 131104 Using the Unified Dynamical Afterglow Model

Abstract

Multi-band observations of the fast radio burst (FRB) 131104 show that this burst may be associated with a gamma-ray transient entitled Swift J0644.5-5111. Follow-up observations for potential X-ray and radio counterparts of FRB 131104/Swift J0644.5-5111 got null results and provided the upper limits of the emission flux at 5.5 GHz, 7.5 GHz, U -band, and X-ray band. By assuming this association and using these upper limits, environmental properties (the fraction of energy in a magnetic field ε B and the number density n) of the progenitor system of FRB 131104/Swift J0644.5-5111 were constrained in the context of the standard afterglow model that neglects the non-relativistic effect and jet effect by several groups. In this paper, we adopt a unified afterglow model that takes into account the non-relativistic effect and jet effect and use the upper limits of four bands (5.5 GHz, 7.5 GHz, U -band, and X-ray) to obtain more stringent constraints on the parameter space spanned by ε B and n. We thus suggest that FRB 131104/Swift J0644.5-5111 might originate from a black holeneutron star merger event. Moreover, we calculate multi-band emissions from a kilonova powered by the radioactivity of r-process elements synthesized in the ejected neutron-rich material and find that the U -band emission from the putative kilonova is significantly lower than the upper limit of the observations.

A living theory catalogue for fast radio bursts

“…In a kilonovae, as the stars coalesce, radioactive elements formed in a rapid neutron capture process (r-process) decay to power optical or near infra-red (NIR) emission. The latter is likely insignificant (Peng et al, 2018), but optical emission may be observable. The signal is isotropic and detectable for a period lasting days to weeks, making kilonovae good candidates for observational detection of counterparts.…”