Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 1046-409

ATel #17864; P. Monti-Guarnieri (University of Trieste and INFN Trieste), S. Wagner (IFAE), C. C. Cheung (NRL), on behalf of the Fermi Large Area Telescope Collaboration
on 2 Jul 2026; 08:13 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 enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar PKS 1046-409, with radio coordinates R.A. = 162.15946 deg, Dec. = 41.23337 deg (J2000; Hunt et al. 2021, AJ, 162, 121), and redshift z=0.62 (Jauncey et al. 1984, ApJ, 286, 498). This source was not present in the fourth Fermi-LAT source catalog up to data release 3 (4FGL-DR3, Abdollahi et al. 2022, ApJS, 260, 53), but it is detected as 4FGL J1048.5-4114 in data release 4 (4FGL-DR4, Ballet et al. 2023, arXiv:2307.12546).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state from June 22 to June 29, 2026, with a weekly averaged gamma-ray flux (E>100MeV) of (1.8 +/- 0.4) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase by a factor of more than 150 relative to the average flux reported in 4FGL-DR4. The corresponding photon index is 2.4 +/- 0.2, indicating a softer spectrum than the 4FGL-DR4 value of 2.0 +/- 0.2.

The transient was identified thanks to the method implemented within the Fermi-LAT Collaboration known as "Fermi All-sky Variability Analysis" that searches the sky for high-energy transients on weekly time scales (Ackermann et al. 2013, ApJ, 771, 57; Abdollahi et al. 2017, ApJ, 846, 34). The report for this flare detection is: Week 934, flare 12. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact persons are C.C. Cheung (Teddy.Cheung@nrl.navy.mil) and Pietro Monti-Guarnieri (pietro.monti-guarnieri@phd.units.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.