2018ApJ...861..147P

Multiband 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 nonrelativistic effect and jet effect by several groups. In this paper, we adopt a unified afterglow model that takes into account the nonrelativistic 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 hole-neutron star merger event. Moreover, we calculate multiband 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.