Implications from the upper limit of radio afterglow emission of FRB 131104/Swift J0644.5-5111

Abstract

A $\gamma$-ray transient, Swift J0644.5-5111, has been claimed to be associated with FRB 131104. The $\gamma$-ray energy output is estimated as $E_{\gamma }\approx 5\times 10^{51}$\,erg at the nominal $z\approx 0.55$ redshift implied by the dispersion measure of FRB 131104. However, a long-term radio imaging follow-up observations only place an upper limit on the radio afterglow flux of Swift J0644.5-5111. Applying the external shock model, we make a detailed constraint on the afterglow parameters for the FRB 131104/Swift J0644.5-5111 system. We find that for the commonly used microphysics shock parameters (e.g., ${\epsilon }_e=0.1$, ${\epsilon }_B=0.01$ and $p=2.3$), if the redshift value inferred from the DM value is correct to order of magnitude (i.e., $z>0.1$), the ambient medium number density should be $\le 10^{-3}\mathrm{c}{\mathrm{m}}^{-3}$, which is the typical value for a compact binary merger environment but disfavors a massive star origin. Assuming a typical ISM density, one would require that the redshift of the FRB much smaller than the value inferred from DM value ($z\ll 0.1$), implying a non-cosmological origin of DM. The constraints are much looser if one adopts smaller ${\epsilon }_B$ and ${\epsilon }_e$ values, as observed in some GRB afterglows. The FRB 131104/Swift J0644.5-5111 association remains plausible. We critically discuss possible progenitor models for the system.

Accepted for publication in ApJL

References in corpus (4)

• A bright millisecond radio burst of extragalactic origin
• A fast radio burst in the direction of the Carina dwarf spheroidal galaxy
• Phenomenology of Reverse-Shock Emission in the Optical Afterglows of Gamma Ray Bursts
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