Fermi-LAT detection of enhanced gamma-ray activity from the radio source FIRST J133101.8+293216
ATel #17043; G. La Mura (INAF - Astronomical Observatory of Cagliari), on behalf of the Fermi Large Area Telescope Collaboration
on 18 Feb 2025; 16:05 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from a source positionally consistent with the radio source FIRST J133101.8+293216, also known as 4FGL J1330.7+2933 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 202.75775 deg, Dec. = +29.53788 deg (J2000; Hardcastle et al. 2016, MNRAS, 462, 1910), and unknown redshift.
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on February 17, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.4+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 110 relative to the average flux reported in the fourth data release of the Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2024, arXiv:2307.12546). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.1+/-0.2, indicating a harder spectrum than the 4FGL-DR4 value of 2.47+/-0.08. The spectral hardening led to the detection of one high energy photon with E=12 GeV, associated with the source with a probability p=0.995 on February 17 at 12:44:04 UT.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Giovanni La Mura (giovanni DOT lamura AT inaf DOT 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.
