Fermi-LAT detection of a new gamma-ray source associated with the flat-spectrum radio source TXS 2138+527
ATel #16760; C. C. Cheung (NRL), G. Marti-Devesa (Univ. and INFN Trieste), D. Bernard (LLR, Ecole Polytechnique & CNRS / IN2P3), on behalf of the Fermi Large Area Telescope Collaboration
on 8 Aug 2024; 19:06 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 gamma-ray emission from a source positionally consistent with the flat-spectrum radio source TXS 2138+527, with radio coordinates R.A. = 324.973435 deg, Dec. = 53.004611 deg (J2000; Immer et al. 2011, ApJS, 194, 25), and unknown redshift. This source is not in any published LAT catalog and was not detected by AGILE or EGRET.
Preliminary analysis indicates that this source was significantly detected (>5 sigma) in a high gamma-ray state on 2024 Aug 7, with a daily averaged gamma-ray flux (E>100MeV) of (4.7+/-1.2) X 10^-7 photons cm^-2 s^-1 and a single power-law photon index of 1.8+/-0.1 (statistical uncertainties only), with a 6-hr peak flux of (8.7+/-2.7) X 10^-7 photons cm^-2 s^-1 (photon index = 1.8+/-0.2) during the 12:00-18:00 interval. Its best-fit LAT position, R.A. = 324.92 deg, Dec. = 52.98 deg (J2000) with an uncertainty of 0.11 deg (95% confidence), is offset by 0.04 deg from the TXS 2138+527 radio position.
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 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.
