Fermi-LAT detection of renewed gamma-ray activity from the FSRQs 4C +27.50 and PKS 1127-14
ATel #17035; Chiara Bartolini (University of Trento & INFN Bari), Ettore Bronzini (University of Bologna & INAF-OAS) on behalf of the Fermi Large Area Telescope Collaboration
on 12 Feb 2025; 17:11 UT
Credential Certification: Chiara Bartolini (chiara.bartolini-1@unitn.it)
Subjects: Gamma Ray, >GeV, AGN, Blazar, Quasar
Referred to by ATel #: 17055
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 (FSRQ) 4C +27.50, also known as 4FGL J2321.9+2734 (4FGL-DR4; Ballet et al. 2024, arXiv:2307.12546), with coordinates RA = 350.49943 deg, Decl. = 27.54623 deg (J2000; Johnston et al. 1995, AJ, 110, 880) and redshift z=1.255 (Sexton et al. 2022, ApJS, 260, 33).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on February 11, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (1.5 +/- 0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 80 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL-DR4). The corresponding photon index is 1.8 +/- 0.1 indicating a significantly harder spectrum than the 4FGL-DR4 value of 2.24 +/- 0.04. On the same day, a high-energy photon (14 GeV) was associated with the source at a confidence level p > 0.998.
The Fermi LAT has also observed enhanced gamma-ray activity from a source positionally consistent with the PKS 1127-14, also known as 4FGL J1129.8-1447 (4FGL-DR4; Ballet et al. 2024, arXiv:2307.12546), with coordinates R.A. = 172.52939 deg, Decl. = 14.82427 (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=1.189 (Jones 2009, MNRAS, 399, 683). Preliminary analysis indicates that PKS 1127-14 was in an elevated gamma-ray emission state on February 11, 2025, reaching a daily averaged gamma-ray flux (E>100MeV) of (1.1+/-0.3) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), which is approximately 20 times higher than the 4FGL-DR4 flux. The corresponding spectral index was 2.6+/-0.1, which is consistent with the 4FGL-DR4 value 2.63 +/- 0.03.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of these sources will continue. Preliminary Fermi-LAT light curves can be accessed via the Fermi-LAT Light-Curve Repository for PKS 1127-14 and via the LAT daily monitored source list for 4C +27.50. We encourage multifrequency observations of these sources. For 4C +27.50, the Fermi-LAT contact person is Giovanni La Mura (giovanni[dot]lamura[at]inaf[dot]it). For PKS 1127-14, the Fermi-LAT contact person is Bindu Rani (binduphysics at gmail.com).
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.
