Fermi LAT detection of a GeV gamma-ray flare from the FSRQ S4 0805+41
ATel #15704; C. C. Cheung (Naval Research Laboratory), G. LaMura (LIP, Portugal), J. Valverde (UMBC/NASA GSFC), on behalf of the Fermi Large Area Telescope Collaboration
on 20 Oct 2022; 21:07 UT
Credential Certification: Teddy Cheung (Teddy.Cheung@nrl.navy.mil)
Subjects: 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 gamma-ray flaring activity from a source positionally consistent with the flat spectrum radio quasar S4 0805+41, also known as 4FGL J0809.3+4053 (Abdollahi et al. 2020, ApJS, 247, 33), with radio coordinates R.A. = 122.23605 deg, Decl. = 40.87914 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=1.419 (Xu et al. 1994, AJ, 108, 395; Schneider et al. 2010, AJ, 139, 2360).
Preliminary analysis indicates that S4 0805+41 was in an elevated gamma-ray emission state with a daily averaged gamma-ray flux (E>100MeV) of (6.2+/-1.6) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only) on October 19, 2022. This corresponds to a flux increase of a factor of up to about 70 with respect to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the highest daily flux ever observed for this source by the LAT. The measured photon index is 2.0+/-0.2, corresponding to a significantly harder spectrum than the 4FGL value of 2.59+/-0.09.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of S4 0805+41 will continue. This source has an entry in the Fermi LAT light curve repository (https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J0809.3+4053). We encourage multifrequency observations of this gamma-ray source. For this source, the Fermi-LAT contact person is C.C. Cheung (teddy.cheung[at]nrl.navy.mil).
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.
