TITLE: GCN CIRCULAR NUMBER: 20269 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-161210 DATE: 16/12/15 16:48:07 GMT FROM: Sara Buson at GSFC/Fermi S. Buson (NASA-GSFC), C.C. Cheung (NRL), D. Kocevski (NASA/MSFC), G. Vianello (Stanford), on behalf of the Fermi-LAT collaboration We report follow-up observations of the very high-energy IceCube-161210 neutrino event (GCN 20247) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2016-12-10 20:06:40 UTC (T0) with J2000 position, RA =46.58 deg, Decl. = 14.98 deg. There are no cataloged >100 MeV gamma-ray sources consistent with the IceCube-161210 localization. The closest gamma-ray source is 3FGL J0250.6+1713, associated with the high-synchrotron peaked flat-spectrum radio quasar, NVSS J025037+171209 (Ackermann et al. 2015 ApJS 810, 14), at a distance of roughly 4 deg and does not show indication of enhanced gamma-ray activity during the 24 hours close to the neutrino detection. The neutrino localization region was outside the LAT field of view at the time of the detection by IceCube. It entered the LAT FoV at ~T0 + 2000 s. We searched for the existence of intermediate (hours to days) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant excess gamma-ray emission (0.1 - 300 GeV) within the I-161210 90% confidence localization. Assuming a power-law spectrum (photon index = 2.2 fixed) for a point source at the IceCube position, the >100 MeV flux upper limits (95% confidence) are < 6.6e-07 ph cm^-2 s^-1 between T0 + 1927 s and T0 + 4413 s (the time interval in which the position of I-161210 entered the LAT field of view for the first time), < 2.7 x 10^-7 ph cm^-2 s^-1 in 24 hours of exposure beginning at T0, and < 3.7 x 10^-8 ph cm^-2 s^-1 in one week of exposure prior to T0. Longer timescale analysis will be made as data become available. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source region will continue. For this source the Fermi LAT contact person is S. Buson (e-mail: sara.buson at nasa.gov). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.