GB6 J2113+1121: A multi-wavelength flaring gamma-ray blazar temporally and spatially coincident with the neutrino event IceCube-191001A

Abstract

A radio-emitting tidal disruption event (AT2019dsg) is proposed as a likely counterpart of the IceCube neutrino event IC-191001A. In this work we have revisited the {\it Fermi}-LAT data in the direction of the neutrino and confirmed no signal at the site of AT2019dsg. Instead, at the edge of the 90\% confidential level error region of this neutrino there is a $\gamma$-ray transient source associated with a blazar GB6 J2113+1121. In May 2019, GB6 J2113+1121 was undergoing an unprecedented $\gamma$-ray flare since the start of the {\it Fermi}-LAT operation, with a variability amplitude about 20-fold. Similar violent flares of GB6 J2113+1121, unobserved before, have been also detected observed in optical bands. Moreover, the blazar remained in a high flux state in the infrared bands when IceCube-191001A arrived, though its $\gamma$-ray and optical activities has temporally ceased. Motivated by the spatial and temporal coincidence, we suggest that GB6 J2113+1121 is a candidate of the counterpart of IC-191001A. The jet properties of GB6 J2113+1121 are investigated, which are found to be comparable with that of the neutrino-emitting blazars (candidates). A specific analysis of archival IceCube data in this direction and future observations would put a further constraint on the origin of the neutrino.