Fermi-LAT detection of renewed gamma-ray activity from the FSRQ MG1 J221916+1806
ATel #17123; Federica Giacchino (INFN Roma2 & SSDC/ASI), G. La Mura (INAF-OACa) on behalf of the Fermi Large Area Telescope Collaboration
on 31 Mar 2025; 16:28 UT
Credential Certification: Federica Giacchino (federica.giacchino@roma2.infn.it)
Subjects: Gamma Ray, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on board the Fermi Gamma-ray Space Telescope, has observed renewed gamma-ray activity from a source positionally consistent with the flat spectrum radio quasar MG1 J221916+1806, also known as 4FGL J2219.2+1806 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. =334.80872 deg, Dec. = 18.10988 deg (J2000; Truebenbach & Darling 2017, ApJS, 233, 3), and redshift z= 1.078 (Xiao et al. 2022, ApJ, 936, 146).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on March 30, 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 release of the Fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2024, arXiv:2307.12546). The corresponding photon index is 1.6+/-0.2, which indicates a significantly harder spectrum than the 4FGL-DR4 value of 2.30+/-0.03. This is the highest LAT daily flux ever observed for this source. The hard spectral state led to the detection of an 11 GeV photon with a probability of being associated with the source of p > 0.98. The Fermi LAT Collaboration has previously reported gamma-ray flaring activity from MG1 J221916+1806 in ATel #6020.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for MG1 J221916+180 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J2219.2+1806. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Federica Giacchino (federica.giacchino@roma2.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.
