GCN Circular 37735
Subject
Fermi-LAT Gamma-ray Observations of NuEm-240926A
Date
2024-10-08T13:29:51Z (5 months ago)
From
Patrik M. Veres at Ruhr University Bochum <veres@astro.ruhr-uni-bochum.de>
Via
Web form
P. M. Veres (Ruhr-Universitaet Bochum), C. Bartolini (INFN Bari), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg) and J. Sinapius (DESY) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the IceCube-HAWC coincidence alert (GCN#37614) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The HAWC event was detected in a 6.06 hours interval from 2024-09-26 at 13:12:19 UT (T0) to 2024-09-26 at 19:01:26 UT with J2000 position RA = 149.97 deg, Decl. = 46.22 deg and a 90% PSF containment of 0.41 deg. One cataloged >100 MeV gamma-ray source is located within the 90% NuEm-240926A localization error, at a distance of roughly 0.12 deg (Fourth Fermi-LAT catalog, 4FGL-DR4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). This is the object 4FGL J0959.6+4606 likely associated with the narrow-line Seyfert 1 galaxy SDSS J095909.51+460014.3 (Li et al. 2023, A&A, 676, A9). Based on a preliminary analysis of the LAT data over the-timescales of 6.06 hours, 1-day and 1-month prior to T0, this object is not significantly detected at gamma-rays.
We searched for short (hours to month) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the NuEm-240926A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the NuEm-240926A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.8e-7 ph cm^-2 s^-1 for ~6.06 hours, < 1.0e-7 ph cm^-2 s^-1 for a 1-day and < 4.6e-9 ph cm^-2 s^-1 for a 1-month 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 person is Patrik M. Veres (veres at astro.ruhr-uni-bochum.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.