Fermi-LAT detection of record gamma-ray flare in BL Lacertae contemporaneous with record optical flaring
ATel #13964; Roopesh Ojha (NASA/GSFC/UMBC) and Janeth Valverde (LLR/Ecole Polytechnique) on behalf of the Fermi Large Area Telescope Collaboration
on 22 Aug 2020; 15:10 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)
Subjects: Optical, Gamma Ray, >GeV, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed record high gamma-ray activity from BL Lacertae (4FGL J2202.7+4216; The Fermi-LAT collaboration 2020, ApJS, 247, 33). This coincides with optical peaks reported recently (Atel #13956, ATel# 13958, ATel# 13930). Preliminary analysis indicates that, since our reported flare on 2020 August 9 (ATel#13933), BL Lacertae has remained in a bright state. On 2020 August 19, it reached its highest daily averaged gamma-ray flux (E>100MeV) of (2.8+/-0.2) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) since the beginning of Fermi-LAT operations in Aug 2008. The corresponding photon index was 2.1 +/- 0.1, which is consistent with the photon index of 2.23 +/- 0.01 reported in the 4FGL catalog.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. The source is included in the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available ( https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/BL_Lac ). We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Simone Garrappa (simone.garrappa at desy.de).
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.
