Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ CGRaBS J1848+3219
ATel #17417; A. Holzmann Airasca (University of Trento & INFN Bari) and G. La Mura (INAF - Astronomical Observatory of Cagliari), on behalf of the Fermi Large Area Telescope Collaboration
on 24 Sep 2025; 18:34 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)
Subjects: Gamma Ray, >GeV, Blazar, Quasar
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 flat-spectrum radio quasar CGRaBS J1848+3219, also known as B2 1846+32A and 4FGL J1848.4+3217 (Abdollahi et al. 2020, ApJS, 247, 33), with coordinates R.A. = 282.09204 deg, Decl. = +32.31739 deg (J2000, Le Bail et al., 2016, AJ, 151, 79), and redshift z=0.798 (Sowards-Emmerd et al. 2005, ApJ, 626, 95).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on September 23, 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 20 relative to the average flux reported in the fourth data release of the fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2023, arXiv:2307.12546). The corresponding photon index is 2.0+/-0.2 indicating a significantly harder spectral state than the one inferred from the average power-law spectral index of 2.42 +/- 0.03 reported in 4FGL-DR4. The Fermi LAT Collaboration has previously reported flaring activity from this source in ATel #2954.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is part of the Fermi-LAT daily Monitored source list, so its daily light curve is available here. A preliminary light curve can also be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J1848.4+3217. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Aldana Holzmann Airasca (a.holzmannairasca@unitn.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.
