Fermi-LAT detection of a possible gamma-ray flare from TXS 1623+578
ATel #16639; Federica Giacchino (INFN Roma Tor Vergata & SSDC) on behalf of the Fermi Large Area Telescope Collaboration
on 5 Jun 2024; 10:01 UT
Credential Certification: Federica Giacchino (federica.giacchino@roma2.infn.it)
Subjects: Gamma Ray, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed for the first time gamma-ray flaring activity from a source positionally consistent with the flat spectrum radio source TXS 1623+578, also known as 4FGL J1623.6+5743 in the fourth Fermi-LAT catalog (The Fermi-LAT collaboration 2020, ApJS, 247, 33) with VLBI coordinates, (J2000.0), R.A: +246.103365 deg, Dec.: +57.687856 deg (Gattano C. et al. 2018A&A,618A,80G). The radio source is a FSRQ with z=0.789 (Vermeulen, R. C et al. 1996AJ, 111.1013V).
Preliminary analysis indicates that on 2024 June 3, TXS 1623+578 was in a high state with a daily average gamma-ray flux (E>100MeV) of (0.2 +/- 0.1) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 85 times greater than the average flux reported in the 4FGL catalog. The corresponding photon index is 2.01+/- 0.33, which is consistent with the 4FGL value of 2.19 +/- 0.13 within the uncertainties.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source we strongly encourage multi wavelength observations. For this source the Fermi-LAT contact person is Federica Giacchino (federica.giacchino@roma2.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.
