Fermi-LAT detection of gamma-ray flaring activity from the BL Lac GB6 J1058+2817
ATel #14491; R. Angioni (SSDC/INFN) on behalf of the Fermi Large Area Telescope Collaboration
on 29 Mar 2021; 17:56 UT
Credential Certification: Roberto Angioni (r.angioni90@gmail.com)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity from a source positionally consistent with the BL Lac GB6 J1058+2817, also known as 4FGL J1058.6+2817 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 164.624562 deg, Decl. = 28.296170 deg (J2000; Petrov & Taylor 2011 AJ, 142, 89), and a tentative redshift z=0.4793 (Massaro et al. 2014 AJ, 148, 66).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 28 March 2021, with a daily averaged gamma-ray flux (E>100MeV) of (3.3+/-1.1) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 45 relative to the average flux reported in the second data release of the fourth Fermi-LAT catalog (4FGL-DR2; Ballet et al., arXiv:2005.11208). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 1.8+/-0.2, and is significantly smaller than the 4FGL-DR2 value of 2.23+/-0.07. This hard-spectrum state was accompanied by the detection of two E>10 GeV photons with a probability >99% of having been emitted by the target source. The highest-energy photon was observed on the same day at 21:53:15.827 UTC, with an energy of ~14 GeV.
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 Roberto Angioni (roberto.angioni@ssdc.asi.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.
