Fermi LAT detection of renewed GeV gamma-ray activity of PKS 1413+135

ATel #15163; Federica Giacchino (INFN Roma Tor Vergata, & ASI Space Science Data Center, Roma, Italy), Stefano Ciprini (INFN Roma Tor Vergata, & ASI Space Science Data Center, Roma, Italy), on behalf of the the Fermi Large Area Telescope Collaboration
on 13 Jan 2022; 22:06 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity from a source positionally consistent with the blazar PKS 1413+135, also known as OQ 122 and 4FGL J1416.1+1320 (Abdollahi, et al. 2020, ApJS, 247, 33), with radio coordinates R.A. = 213.9951 deg, Decl. = +=13.3399 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.24671+/-0.00001 (Wiklind & Combes 1997, A&A, 328, 48). Initially classified as a BL Lac, it might also be a young radio source (Perlman et al. 1996 AJ, 111, 1839; Gugliucci et al. 2005 ApJ, 622, 136).

Preliminary analysis indicates that PKS 1413+135 was in an elevated gamma-ray emission state during the past days, reaching daily averaged gamma-ray fluxes (E>100MeV) of (2.2+/-0.7) X 10^-7 photons cm^-2 s^-1 and (2.0+/-0.6) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only) respectively on January 11 and January 12, 2022. These correspond to a flux increase of a factor of about 20 with respect to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon indices are 1.7+/-0.2 for each day, significantly smaller than the 4FGL value of 2.41+/-0.07. This hard-spectrum state was accompanied by the detection of several photons with probability >99% of having been emitted by the target source. The highest energy photon was observed on 11 January 2022, with an energy of about 25 GeV.

This is the second time that the Fermi LAT Collaboration has reported enhanced gamma-ray activity from PKS 1413+135 (ATel#13049). The MAGIC Cherenkov telescopes have recently reported the first detection of VHE gamma-ray emission above 150 GeV from this object (ATel#15161).

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of PKS 1413+135 will continue. This source is part of the "FSSC 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_1413p135. This source has also an entry in the FSSC light curve repository (https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.php?source_name=4FGL_J1416.1+1320). We encourage multifrequency observations of this gamma-ray source. For this source, the Fermi-LAT contact persons are F. Giacchino (federica.giacchino@roma2.infn.it) and C.C. Cheung (teddy.cheung@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.