Fermi-LAT detection of enhanced gamma-ray activity from PKS 1413+135
ATel #17155; Omer Faruk Coban (Institute of Space Sciences, ICE-CSIC) on behalf of the Fermi Large Area Telescope Collaboration
on 21 Apr 2025; 10:28 UT
Credential Certification: Janeth Valverde (valverde@llr.in2p3.fr)
Subjects: Gamma Ray, >GeV, VHE, 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 PKS 1413+135, also known as 4FGL J1416.1+1320 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 213.99507 deg, Dec. = 13.33992 deg (J2000; Xu et al. 2019, ApJS, 242, 26), and redshift z = 0.247 (Wiklind & Combes 1997, A&A, 328, 48).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on April 19, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.5+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This value is about 20 times larger than the average flux reported in the fourth release of the Fourth Fermi-LAT catalog (4FGL-DR4; Ballet et al. 2024, arXiv:2307.12546). The corresponding photon index is 1.6+/-0.1, indicating a significantly harder spectrum than the 4FGL-DR4 value of 2.07+/-0.02. One high-energy photon with E = 92 GeV was associated with the source on April 19 at 17:17:30 UT with a probability p > 0.99. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #13049, #15163, and #16123. The MAGIC Cherenkov telescopes also reported a 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 this source will continue. This source is included in the "LAT Monitored Sources", and a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available here. A preliminary light curve for PKS 1413+135 can be accessed via the Fermi-LAT Light-Curve Repository. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is 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.
