Radio-interferometric Monitoring of FRB 131104: A Coincident AGN Flare, but No Evidence for a Cosmic Fireball

Abstract

The localization of fast radio bursts (FRBs) has been hindered by the poor angular resolution of the detection observations and inconclusive identification of transient or variable counterparts. Recently a γ-ray pulse of 380 s duration has been associated with FRB 131104. We report on radio-continuum imaging observations of the original localization region of the FRB, beginning three days after the event and comprising 25 epochs over 2.5 years. We argue that the probability of an association between the FRB and the γ-ray transient has been overestimated. We provide upper limits on radio afterglow emission that would be predicted if the γ-ray transient was associated with an energetic γ-ray burst. We further report the discovery of an unusual variable radio source spatially and temporally coincident with FRB131104, but not spatially coincident with the γ-ray event. The radio variable flares by a factor of 3 above its long-term average within 10 day of the FRB at 7.5 GHz, with a factor-of-2 increase at 5.5 GHz. Since the flare, the variable has persisted with only modest modulation and never approached the flux density observed in the days after the FRB. We identify an optical counterpart to the variable. Optical and infrared photometry, and deep optical spectroscopy, suggest that the object is a narrow-line radio active galactic nucleus.

A living theory catalogue for fast radio bursts

“…The emission is consistent with a gamma ray burst (GRB). The presence an expected multi-wavelength afterglow was not observed (Shannon and Ravi, 2017), but arguably may not be observable (Gao and Zhang, 2017). A high-energy (GeV) γ-ray afterglow is not affected by environment density, but searches for such signals have yielded null results (Xi et al, 2017).…”

Fast Radio Bursts - implications for Fermi and future prospects

“…The association claim was however refuted [32] based on the non-detection of a radio afterglow at the location of the gamma-ray transient and the discovery of an AGN both temporally and spatially coincident with the FRB. Data taken with the Fermi gamma-ray burst monitor was searched for gamma-ray bursts associated with the repeating FRB 121102 during the time it was visible to the Fermi sky [22].…”

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

“…The follow-up observations performed by the XRT and the UVOT on board Swift two days after Swift was triggered by Swift J0644.5-5111 didn't detect X-ray and optical counterparts (DeLaunay et al 2016). Shannon & Ravi (2017) observed the 5.5 GHz and 7.5 GHz counterparts of FRB 131104 three days to 2.5 years after the FRB trigger and found that the upper limits of the 5.5 GHz and 7.5 GHz are 70 µJy and 100 µJy, respectively.…”

“…A powerful tool to determine the progenitor system of Swift J0644.5-5111 is to research the properties of its environment, e.g., the number density (n) of the interstellar medium (ISM) surrounding the progenitor. Assuming that Swift J0644.5-5111 was associated with FRB 131104 and using the upper limit of 5.5 GHz counterpart of FRB 131104 reported by Shannon & Ravi (2017), Murase et al (2017) constrained the density of the ISM of FRB 131104 with the external shock model of afterglows and concluded that n 2 × 10 −3 cm −3 . By using the same model and the upper limits of radio counterparts and adopting different values of redshift, the fraction of energy in magnetic field (ε B ), and the fraction of energy in electrons (ε e ), Gao & Zhang (2017) constrained the parameter space of the ISM density.…”