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GCN Circular 32528

Subject
Fermi-LAT Gamma-ray Observations of IceCube-220907A
Date
2022-09-07T21:42:57Z (2 years ago)
From
Sara Buson at GSFC/Fermi <sara.buson@gmail.com>
J. Sinapius (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg), S. Garrappa (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the IceCube-220907A high-energy neutrino event (GCN 32523Loading...
 
 ) 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 2022-09-07 at 06:46:47.52 UT (T0) with J2000 position RA = 224.81 (+2.07, -1.95) deg, Decl. = +44.70 (+0.94 , -1.06) deg (90% PSF containment). One cataloged gamma-ray (>100 MeV) source is located within the 90% IC220907A localization region at a distance of roughly 1.38 deg (4FGL-DR3; The Fermi-LAT collaboration 2022, ApJS, 260, 53). This is the unassociated gamma-ray source 4FGL J1504.6+4343. Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma).

We searched for intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC220907A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC220907A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.5e-10 ph cm^-2 s^-1 for ~14-years (2008-08-04 to 2022-09-07 UTC), and < 1.1e-8 (< 4.7e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.

Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For these observations the Fermi-LAT contact persons are J. Sinapius (jonas.sinapius at desy.de), 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.