AGILE Detection of a Candidate Gamma-Ray Precursor to the ICECUBE-160731 Neutrino Event
F. Lucarelli ; C. Pittori ; F. Verrecchia ; I. Donnarumma ; et al.
Sep - 2017
DOI: 10.3847/1538-4357/aa81c8

journal : The Astrophysical Journal

Volume : 846 ; Issue : 2
type: Article Journal

Abstract
On 2016 July 31 the ICECUBE collaboration reported the detection of a high-energy starting event induced by an astrophysical neutrino. Here, we report on a search for a gamma-ray counterpart to the ICECUBE-160731 event, made with the AGILE satellite. No detection was found spanning the time interval of ±1 ks around the neutrino event time T 0 using the AGILE "burst search" system. Looking for a possible gamma-ray precursor in the results of the AGILE-GRID automatic Quick Look procedure over predefined 48-hr time bins, we found an excess above 100 MeV between 1 and 2 days before T 0, which is positionally consistent with the ICECUBE error circle, that has a post-trial significance of about $4\sigma$. A refined data analysis of this excess confirms, a posteriori, the automatic detection. The new AGILE transient source, named AGL J1418+0008, thus stands as a possible ICECUBE-160731 gamma-ray precursor. No other space missions nor ground observatories have reported any detection of transient emission consistent with the ICECUBE event. We show that Fermi-LAT had a low exposure for the ICECUBE region during the AGILE gamma-ray transient. Based on an extensive search for cataloged sources within the error regions of ICECUBE-160731 and AGL J1418+0008, we find a possible common counterpart showing some of the key features associated with the high-energy peaked BL Lac (HBL) class of blazars. Further investigations on the nature of this source using dedicated SWIFT ToO data are presented.

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