TITLE: GCN CIRCULAR NUMBER: 24989 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-190704A and detection of the new gamma-ray source 1WHSP J104516.2+275133 DATE: 19/07/05 23:57:36 GMT FROM: Sara Buson at GSFC/Fermi S. Garrappa (DESY-Zeuthen, DE), S. Buson (Univ. of Wuerzburg, DE; UMBC, USA) and T. Venters (NASA-GSFC, USA) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC190704A neutrino event (GCN 24981) 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 2019-07-04 at 18:48:52.25 UTC (T0) with J2000 position RA = 161.85 (+2.16 -4.33) deg, Decl. = 27.11 (+1.81 -1.83) deg 90% PSF containment. One cataloged >0.1 MeV gamma-ray source is located within the 90% IC190704A localization error, at a distance of roughly 0.8 deg. This is the unassociated object 4FGL J1049.8+2741 (The Fermi-LAT collaboration, 2019, arXiv:1902.10045). In a preliminary analysis of the LAT data over one day and one month prior T0, this object is not significantly detected in the LAT data. Preliminary analysis indicates no significant (>5sigma) excess emission (0.1 - 800 GeV) at the IC190704A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IceCube best-fit position, the >0.1 GeV flux upper limit (95% confidence) is <1.5e-10 ph cm^-2 s^-1 for ~10.9-years (2008-08-04 / 2019-07-05), < 6e-9 (< 5e-7) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. In the analysis of the 10.9-years integrated LAT data (0.1 - 800 GeV), a >5 sigma new excess of gamma rays was detected 0.8 deg offset from the best-fit IC190704 position and within the 90% confidence localization of the direction of the neutrino. Assuming a power-law spectrum, the best-fit localization is (J2000) RA: 161.343, Dec: 27.848 (0.08 deg 99% containment, 0.03 deg 68% containment). The most likely counterpart is the blazar 1WHSP J104516.2+275133 (a.k.a. Arsioli et al. 2015, A&A 579 34), located 0.025 deg away from the best-fit position of the gamma-ray excess, and within its 68% containment. The gamma-ray best-fit spectral parameters are flux = (7.8 +/- 3.5)e-10 ph cm^-2 s^-1 and index = 1.8 +/- 0.1. In a preliminary analysis of the LAT data over one day and one month prior T0, 1WHSP J104516.2+275133 is not significantly detected in the LAT data. The hard gamma-ray spectrum and detection of >100GeV photons positionally consistent with the blazar make this object a promising TeV candidate. We strongly encourage multiwavelength observations of this potentially compelling source, positionally consistent with the IceCube neutrino IC190704A. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source and of the neutrino region will continue. For this source the Fermi-LAT contact persons are S. Garrappa (simone.garrappa at desy.de ) and S. Buson (sara.buson at uni-wuerzburg.de ). 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.