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 $\gamma$-ray pulse of $380$ s duration has been associated with the fast radio burst 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 yr. Besides probabilistic arguments that suggest that the association between the $\gamma$-ray transient and the FRB is not compelling, we provide upper limits on a putative radio afterglow of this transient that are at odds with standard models for its progenitor. We further report the discovery of an unusual variable radio source spatially and temporally coincident with FRB 131104, but not spatially coincident with the $\gamma$-ray event. The radio variable flares by a factor of $3$ above its long term average within $10$ d of the FRB at 7.5 GHz, with a factor-of-$2$ increase at $5.5$ GHz. Within our observations, 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 AGN.

8 pages, 3 Figures, submitted to ApJ Letters

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Cited by in corpus (8)

• Fast Radio Bursts
• INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154
• Multiwavelength observations of Fast Radio Bursts
• Deep optical observations contemporaneous with emission from the periodic FRB 180916.J0158+65
• Zwicky Transient Facility constraints on the optical emission from the nearby repeating FRB 180916.J0158+65
• Search for GeV counterparts to fast radio bursts with Fermi
• FRB131104 Swift BAT data revisited: No evidence of a gamma-ray counterpart
• Detectability of radio afterglows from binary neutron star mergers and implications for fast radio bursts