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AGILE confirmation of gamma-ray activity from the IceCube-170922A error region

ATel #10801; F. Lucarelli (SSDC/ASI and INAF/OAR), G. Piano (INAF/IAPS), C. Pittori, F. Verrecchia (SSDC/ASI and INAF/OAR), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Bulgarelli (INAF/IASF-Bo), P. Munar-Adrover, G. Minervini, A. Ursi (INAF/IAPS), S. Vercellone (INAF/OA-Brera), I. Donnarumma (ASI), V. Fioretti, A. Zoli (INAF/IASF-Bo), E. Striani (CIFS and INAF/IAPS), M. Cardillo (INAF/OA-Arcetri and INAF/IAPS), F. Gianotti, M. Trifoglio (INAF/IASF-Bo), A. Giuliani, S. Mereghetti, P. Caraveo, F. Perotti (INAF/IASF-Mi), A. Chen (Wits University), A. Argan, E. Costa, E. Del Monte, Y. Evangelista, M. Feroci, F. Lazzarotto, I. Lapshov, L. Pacciani, P. Soffitta, S. Sabatini, V. Vittorini (INAF/IAPS), G. Pucella, M. Rapisarda (ENEA-Frascati), G. Di Cocco, F. Fuschino, M. Galli, C. Labanti, M. Marisaldi (INAF/IASF-Bo), A. Pellizzoni, M. Pilia, A. Trois (INAF/OA-Cagliari), G. Barbiellini, E. Vallazza (INFN Trieste), F. Longo (Univ. Trieste and INFN Trieste), A. Morselli, P. Picozza (INFN and Univ. Roma Tor Vergata), M. Prest (Univ. dell'Insubria), P. Lipari, D. Zanello (INFN and Univ. Roma Sapienza), P. W. Cattaneo, A. Rappoldi (INFN Pavia), S. Colafrancesco (INAF/OAR and Wits University), N. Parmiggiani (University of Modena and Reggio Emilia), A. Ferrari (Univ. Torino and CIFS), F. Paoletti (East Windsor RSD Hightstown and INAF/IAPS), A. Antonelli (SSDC/ASI), P. Giommi, L. Salotti, G. Valentini, and F. D'Amico (ASI)
on 29 Sep 2017; 15:41 UT
Credential Certification: Fabrizio Lucarelli (fabrizio.lucarelli@asdc.asi.it)

Subjects: Gamma Ray, >GeV, Neutrinos

Referred to by ATel #: 10817, 10830, 10838, 10840, 10844, 10845, 10861

Following the IceCube observation of a high-energy neutrino candidate event, IceCube-170922A, at T0 = 17/09/22 20:54:30.43 UT (https://gcn.gsfc.nasa.gov/gcn3/21916.gcn3), and the detection of increased gamma-ray activity from a previously known Fermi-LAT gamma-ray source (3FGL J0509.4+0541) in the IceCube-170922A error region (ATel #10791), we have analysed the AGILE-GRID data acquired in the days before and after the neutrino event T0, searching for significant gamma-ray excess above 100 MeV from a position compatible with the IceCube and Fermi-LAT error regions.

On a 3-day integration starting from 2017-09-18 12:00 UT, a preliminary maximum likelihood analysis yields a detection at about 4 sigma significance level with a flux F(E>100 MeV)=(1.3 +/- 0.5) x 10^-6 ph cm^-2 s^-1, centered at Galactic coordinates (l, b)=(196.1, -20.3) +/- 0.7 deg (95% stat. c.l.) +/- 0.1 deg (syst.) (R.A., Decl. (J2000): 77.13, 4.79 deg), less than 1 degree both from the IceCube centroid and from the position of 3FGL J0509.4+0541. The AGILE detection occurs within the Fermi-LAT reported period of increase in gamma-ray activity.

A preliminary search for a peak flux in the range (T0 +/- 6) days shows that the maximum emission occurs between one or two days before the neutrino detection time. This might confirm a result found by AGILE, regarding the detection of a possible gamma-ray precursor of a previous IceCube HESE event, IceCube-160731 (Lucarelli et al., ApJ 846 (2017)).

Gamma-ray activity from this region was previously reported by AGILE in 2014 (ATel #6457).

This measurement was obtained with AGILE observing a large portion of the sky in spinning mode. Multifrequency observations of the AGILE error circle are strongly encouraged.