Support ATel At Patreon

[ Previous | Next | ADS ]

Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ source TXS 0646-176

ATel #14980; Giovanni La Mura (LIP)
on 18 Oct 2021; 06:43 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)

Subjects: Gamma Ray, >GeV, AGN, Blazar

Referred to by ATel #: 14981, 14987, 14991, 14993, 14999, 15000

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar TXS 0646-176, also known as 4FGL J0648.4-1743 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with radio coordinates R.A. = 102.1187437 deg, Decl. = -17.7348444 deg (J2000; Petrov et al. 2006, AJ, 131, 1872), and redshift z=1.232 (Murdoch et al. 1984, PASA, 5, 341).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 2021 October 14, with a daily averaged gamma-ray flux (E>100MeV) of (3.4 +/- 0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), and a photon index of 2.3 +/- 0.1. This is slightly below the highest LAT daily flux ever observed for this source (ATel #12327). The high state persisted on 2021 October 15, with a daily averaged gamma-ray flux (E>100MeV) of (3.3 +/- 0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 60 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 2.0 +/- 0.1, and is significantly smaller than the 4FGL value of 2.45 +/- 0.03. Previous flaring episodes were reported in ATel #7833, #11706, #12327 and #14786.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is included in the "LAT Monitored Sources" and, consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available ( http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/ ). We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is S. Ciprini (stefano.ciprini@ssdc.asi.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.