Fermi-LAT detection of a new gamma-ray flare associated with the quasar TXS 1700+685
ATel #14463; C. C. Cheung (NRL), R. Angioni (SSDC/INFN), on behalf of the Fermi Large Area Telescope Collaboration
on 16 Mar 2021; 17:09 UT
Credential Certification: Teddy Cheung (Teddy.Cheung@nrl.navy.mil)
Subjects: Gamma Ray, >GeV, Blazar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray flaring activity from a source positionally consistent with the flat-spectrum radio quasar TXS 1700+685, also known as GB6 J1700+6830 (4FGL J1700.0+6830; Abdollahi et al. 2020, ApJS, 247, 33), with coordinates R.A. = 255.0387196 deg, Decl. = +68.5019331 deg (J2000; Petrov et al. 2008. AJ, 136, 580), and redshift z=0.301 (Henstock et al. 1997, MNRAS, 290, 380).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 2021 March 15, with a daily averaged gamma-ray flux (E>100MeV) of (1.1 +/- 0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) and the detection of a ~29 GeV photon. The daily value corresponds to a flux increase of a factor of ~20 relative to the 10-year average flux reported in the fourth Fermi LAT source catalog Data Release 2 (4FGL-DR2; Ballet et al., arXiv:2005.11208). The corresponding photon index is 2.0 +/- 0.1, and is significantly smaller than the 4FGL-DR2 value of 2.377 +/- 0.017. The Fermi LAT Collaboration previously reported flaring from this source in 2009 March at a similar flux level (ATel #1986).
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 S. Cutini (sara.cutini at pg.infn.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.
