Fermi-LAT detection of enhanced gamma-ray activity from TXS 2002-233
ATel #16459; Pfesesani van Zyl (SARAO), I. Mereu (INFN Perugia), on behalf of the Fermi Large Area Telescope Collaboration
on 18 Feb 2024; 20:56 UT
Credential Certification: Janeth Valverde (valverde@llr.in2p3.fr)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a gamma-ray flare from a source positionally consistent with the flat-spectrum radio quasar TXS 2002-233, also known as 4FGL J2005.9-2309 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 301.476 deg, Decl. = -23.153 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.83 (Ajello et al. 2022, ApJS, 263, 9).
A dedicated analysis indicates that this source was in an elevated gamma-ray emission state on February 14, 2024, with a daily averaged gamma-ray flux (E>100MeV) of (0.6 +/- 0.2) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), corresponding to a flux increase of a factor of about 20 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). On February 15, 2024 the flux increased to (1.4 +/- 0.5) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) from 18:00-24:00 UTC. The photon index is 1.9 +/- 0.2, corresponding to a significantly harder spectrum than the 4FGL value of 2.47 +/- 0.05. This is the first report of enhanced activity from PKS 2002-233, although inspection of the Fermi Lightcurve Repository https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J2005.9-2309 indicates that flaring activity also occurred in 2014.
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, especially in light of the large redshift and hard spectrum. For this source, the Fermi-LAT contact person is Pfesesani van Zyl (pvanzyl@sarao.ac.za).
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.
