Fermi-LAT detection of renewed gamma-ray activity from the FSRQ PKS 1424-41
ATel #15807; G. La Mura (LIP, Portugal), on behalf of the Fermi Large Area Telescope Collaboration
on 13 Dec 2022; 10:17 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 renewed gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar PKS 1424-41, also known as 4FGL J1427.9-4206 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 216.98457 deg, Decl. = -42.10540 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z = 1.522 (White et al. 1988, ApJ, 327, 561).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on December 11, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (4.9+/-0.4) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 10 relative to the average flux reported in the third release of the fourth Fermi-LAT catalog (4FGL-DR3, Abdollahi et al. 2022, ApJS, 260, 53). The source exhibited increased optical and gamma-ray activity starting from July 23, 2022 (ATel #15525) and remained in a high gamma-ray state over the following weeks (ATels #15527, #15533), with flux enhancements also in radio (ATel #15536) and optical frequencies (ATel #15552). The current state is the highest LAT daily flux ever reported for this source. The corresponding photon index is 1.81+/-0.05, and is significantly smaller than the 4FGL-DR3 value of 2.20+/-0.01, indicating substantial spectral hardening, with high-energy photons detected up to 21 GeV.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is included among the LAT Monitored Sources and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_1424-41. A preliminary light-curve is also provided through the Fermi-LAT Light Curve Repository (LCR) at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J1427.9-4206. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Francesco Longo (francesco DOT longo AT ts DOT infn DOT 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.
