Fermi-LAT detection of renewed gamma-ray activity from the FSRQ CTA 102

ATel #18104; P. Monti-Guarnieri (University of Trieste and INFN Trieste), on behalf of the Fermi Large Area Telescope Collaboration
on 13 Oct 2026; 18:03 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)

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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 CTA 102, also known as 4FGL J2232.6+1143 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 338.15170 deg, Dec. = +11.73081 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=1.037 (Schmidt 1965, ApJ, 141, 1295).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 2026 October 12, with a daily averaged gamma-ray flux (E>100MeV) of (6.7+/-0.8) 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 fourth data release of the fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2023, arXiv:2307.12546). The peak 3-hour integrated gamma-ray flux (E>100 MeV) of (10.6+/-2.1) X 10^-6 photons cm^-2 s^-1 was reached by CTA 102 on 2026 October 12 in the interval 15:00-18:00 UT. The corresponding daily-averaged photon index is 1.86+/-0.07, indicating a harder spectrum than the 4FGL-DR4 value of 2.303+/-0.004. The spectral hardening led to the detection of two photons with energy greater than 10 GeV associated with the source at a confidence level p > 0.999 on October 12. The highest energy event was a 24 GeV photon observed at 21:36:43 UT. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #3320, #4409, #6631, #8478, #8722, #9869 and #10292.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source belongs to the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available at CTA_102. A preliminary light curve for CTA 102 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL_J2232.6+1143. We encourage multifrequency observations of this source. The Fermi LAT contact persons for this source are S. Cutini (sara.cutini@pg.infn.it) and S. Buson (sara.buson@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.