GCN Circular 34932

S. Buson (Uni Wuerzburg), S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari)  and J. Sinapius (DESY) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IC231027A  high-energy neutrino event (GCN 34891
Not found
 
 
) 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 2023-10-27 at 04:16:10.44 UT (T0) with J2000 position RA =  267.16 (+3.35, -3.40) deg, Decl. = +46.96 (+2.25, -2.88) deg (90% PSF containment).  According to the fourth Fermi LAT source catalog (4FGL-DR4), there are eight 4FGL-DR4 cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources in the 90% IC231027A uncertainty localization region. 
We searched for intermediate (days to years) timescale emission from a new gamma-ray source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC231027A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC231027A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 7.0e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-10-27 UTC), and < 5.2e-9 (< 1.4e-7) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.
The gamma-ray source nearest to the best-fit position of IC231027A is the blazar 4FGL J1747.9+4704 (a.k.a. B3 1746+470, 5BZB J1747+4658), at a 0.16deg separation. Close to the neutrino-event best-fit position, at 0.29deg separation, there is also the unassociated gamma-ray source 4FGL J1749.6+4716. Preliminary analysis indicates that these gamma-ray sources are ongoing a prolonged, enhanced activity state. The year-binned gamma-ray light curves show that they entered the high state in 2021. During the last year, i.e. 1-year integration time before T0, the observed flux (E>100 MeV) of 4FGL J1747.9+4704 is (1.2 +/- 0.3) x 10^-9 photons cm^-2 s^-1 (statistical uncertainty only), more than three times greater than the average flux reported in the 4FGL-DR4; the flux (E>100 MeV) observed for 4FGL J1749.6+4716 during this same period is of (2.3 +/- 0.3) x 10^-8 photons cm^-2 s^-1 (statistical uncertainty only), more than ten times greater than the 4FGL-DR4 average flux. We encourage multiwavelength observations of these sources. 
We performed an analysis of the region selecting only the LAT higher energy events (>1GeV) in order to achieve an improved localisation of the unassociated source 4FGL J1749.6+4716, and obtain as best-fit position RA = 267.3962, Decl. = 47.3276 (0.04 deg 68% containment, 0.07 deg 95% containment). A plausible association is the flat-spectrum radio source B3 1748+473 (GB6 B1748+4720), located 0.01deg away from the best-fit position.
Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For these observations the Fermi-LAT contact persons are S. Buson (sara.buson at uni-wuerzburg.de <http://uni-wuerzburg.de/>), S. Garrappa (simone.garrappa at weizmann.ac.il <http://weizmann.ac.il/>), J. Sinapius (jonas.sinapius at desy.de <http://desy.de/>), C. Bartolini (chiara.bartolini at ba.infn.it <http://ba.infn.it/>).
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.