Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ TXS 1155+486
ATel #16609; G. La Mura (INAF - O. A. Cagliari) on behalf of the Fermi Large Area Telescope Collaboration
on 2 May 2024; 20:14 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar
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 1155+486, also known as GB1 1155+486 and 4FGL J1158.5+4824 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 179.61154 deg, Decl. = +48.42117 deg (J2000; Beasley et al. 2002, ApJS, 141, 13), and redshift z=2.036 (Albareti et al. 2017, ApJS, 233, 25).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on May 1, with a daily averaged gamma-ray flux (E>100MeV) of (0.4+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of more than 30 relative to the average flux reported in the fourth data release of the fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2024, arXiv:2307.12546). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.3+/-0.2, and is consistent with the 4FGL value of 2.47+/-0.05 within the uncertainties.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for 4FGL J1158.5+4824 can be accessed via the Fermi-LAT Light-Curve Repository at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J1158.5+4824. We encourage multi-frequency observations of this source. For this source, the Fermi-LAT contact person is G. La Mura (giovanni.lamura@inaf.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.
