Fermi-LAT Detection of a Bright Gamma-ray Flare in the BL Lac S5 1803+784
ATel #13633; T. Venters (NASA/GSFC, USA), R. Angioni (SSDC/INFN, Italy), R. Ojha (NASA/GSFC/UMBC, USA) on behalf of the Fermi-LAT Collaboration
on 14 Apr 2020; 03:12 UT
Credential Certification: Tonia Venters (tonia.m.venters@nasa.gov)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed renewed gamma-ray flaring activity from a source positionally consistent with the BL Lac S5 1803+784, also known as 4FGL J1800.6+7828 (4FGL; The Fermi-LAT collaboration 2020, ApJS, 247, 1), with coordinates R.A. = 270.1891 deg, Decl. = +78.4678 deg (J2000; The Gaia Collaboration 2018, A&A, 616, A1), and redshift z = 0.684 (Stickel et al. 1993, A&AS, 98, 393).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 12 April 2020, with a daily averaged gamma-ray flux (E>100MeV) of (1.5+/-0.2) 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 Fermi-LAT catalog (4FGL). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.2+/-0.1, which is similar to the 4FGL value of 2.21+/-0.01. For comparison Fermi-LAT observations for this source during gamma-ray flaring activity, see ATels #2386 and #3322.
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 Tonia Venters (tonia.m.venters@nasa.gov).
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.
