Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 2204-54, and renewed gamma-ray activity from the FSRQ TXS 0358+210
ATel #16085; J. Forman (SURA / CRESST II / NASA GSFC), I. Mereu (INFN Perugia), J. Valverde (UMBC/ NASA GSFC), on behalf of the Fermi Large Area Telescope Collaboration
on 13 Jun 2023; 22:23 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 enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar (FSRQ) PKS 2204-54, also known as 4FGL J2207.5-5346 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with radio coordinates R.A. = 331.932222 deg, Decl. = -53.776061 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=1.206 (Murphy et al. 2019, MNRAS, 482, 3458).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on June 11, 2023 , with a daily averaged gamma-ray flux (E>100MeV) of (0.3+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 20 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 1.9+/-0.2, indicating a harder spectrum than the 4FGL value of 2.43+/-0.04.
The Fermi-LAT has also observed renewed gamma-ray activity from a source positionally consistent with the FSRQ TXS 0358+210, also known as 4FGL J0401.7+2112, with radio coordinates R.A. = 60.438192 deg, Decl. = 21.174607 deg (J2000; Beasley et al. 2002, ApJS, 141, 13), and redshift z=0.834 (Sowards-Emmerd et al. 2005, ApJ 626, 95).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on June 11, 2023, with a daily averaged gamma-ray flux (E>100MeV) of (1.4+/-0.4) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 85 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 2.3+/-0.2, and is consistent with the 4FGL value of 2.40+/-0.05 within the uncertainties. This is second time that the Fermi-LAT Collaboration has announced flaring gamma-ray activity from TXS 0358+210 (ATel #13354).
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of these sources will continue. A preliminary light curve for PKS 2204-54 can be accessed via the Fermi-LAT Light-Curve Repository at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/lcr/source.html?source_name=4FGL_J2207.5-5346. A preliminary light curve for TXS 0358+210 can be accessed via the Fermi-LAT Light-Curve Repository at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/lcr/source.html?source_name=4FGL_J0401.7+2112. We encourage multifrequency observations of these sources. For PKS 2204-54, the Fermi-LAT contact person is Jordan Forman (jforman2018@my.fit.edu). For TXS 0358+210 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.
