Fermi-LAT detection of gamma-ray flaring activity from the radio galaxy 3C 111
ATel #14581; G. La Mura (LIP), R. Angioni (SSDC/INFN), C. C. Cheung (NRL), E. Torresi (INAF-OAS Bologna) on behalf of the Fermi Large Area Telescope Collaboration
on 27 Apr 2021; 22:01 UT
Credential Certification: Roberto Angioni (r.angioni90@gmail.com)
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 FRII (Fanaroff & Riley 1974, MNRAS, 167, 31) Broad Line Radio Galaxy 3C 111, also known as 4FGL J0418.2+3807 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 64.653 deg, Decl. = +38.028 deg (J2000; Fey et al., 2004, AJ, 127, 3587), and redshift z=0.0491 (Eracleous & Halpern, 2004, ApJS, 150, 181). This source has shown rare and intense flares in the past (e.g. Grandi et al. 2012, ApJ, 751, 3).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 2021-04-26, with a daily averaged gamma-ray flux (E>100MeV) of (8+/-2) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of about 20 relative to the 10-year average flux reported in the second data release of the fourth Fermi-LAT catalog (4FGL-DR2; Ballet et al., arXiv:2005.11208). The corresponding photon index is 1.8+/-0.2, and is significantly smaller than the 4FGL-DR2 value of 2.74+/-0.06. The hard-spectrum state was accompanied by the detection of a photon with an energy of 10 GeV with probability >99% of being emitted by 3C 111, at 2021-04-26 02:57:46 UTC.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Target of opportunity observations with the Neil Gehrels Swift Observatory have been proposed. We encourage further multifrequency observations of this source. For this source, the Fermi-LAT contact person is Giovanni La Mura (glamura@lip.pt).
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.
