[vsnet-grb-info 28536] Fermi-LAT Gamma-ray Observations of IceCube-210811A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30639
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-210811A
DATE:    21/08/12 23:59:33 GMT
FROM:    Simone Garrappa at DESY  <simone.garrappa at desy.de>

S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and R. de 
Menezes (Univ. of Sao Paulo, Univ. of Wuerzburg) on behalf of the 
Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy 
IC210811A neutrino event (GCN 30627) 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 2021-08-11 at 02:02:44.04 
UT (T0) with J2000 position RA = 270.79 (+ 1.07, - 1.08) deg, Decl. = 
25.28 (+ 0.79, - 0.84) deg (90% PSF containment). One cataloged 
gamma-ray (>100 MeV) source is located within the 90% IC210811A 
localization region (4FGL-DR2, The Fermi-LAT collaboration 2020, ApJS, 
247, 33). This is the unassociated source 4FGL J1803.3+2425. Based on a 
preliminary analysis of the LAT data over the timescale of 1-day and 
1-month prior to T0, this object is 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 IC210811A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC210811A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 5.3e-10 ph cm^-2 s^-1 for 
~13-years (2008-08-04 to 2021-08-11 UTC), and < 5.0e-8 (< 1.3e-7) 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 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.