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From: atel@astronomerstelegram.org
Subject: ATel  17731
Message-Id: <20260330070315.B95D428807B4@server.astronomerstelegram.org>
Date: Mon, 30 Mar 2026 03:03:15 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17731							     ATEL #17731

Title:	Fermi-LAT detection of renewed gamma-ray activity from the
		FSRQ OI 280
Author:	Petra Benke (GFZ, MPIfR),  on behalf of the Fermi Large Area
		Telescope Collaboration
Queries:	benke@gfz.de
Posted:	29 Mar 2026; 21:07 UT
Subjects:Gamma Ray, >GeV, Request for Observations, AGN, Quasar

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 OI
280, also known as 4FGL J0750.8+1229 (Abdollahi et al. 2022, ApJS, 260,
53), with coordinates R.A. = 117.71688 deg, Dec. = +12.51801 deg (J2000;
Le Bail et al. 2016, AJ, 151, 3, 79), and redshift z=0.889 (Torrealba et
al. 2012, RMxAA, 48, 9).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on March 28, 2026 , with a daily averaged gamma-ray flux
(E>100MeV) of (1.5+/-0.4) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty
only). This corresponds to a flux increase of a factor of nearly 70 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). This is the highest
LAT daily flux ever observed for this source. The corresponding photon
index is 2.0+/-0.1, and indicates a harder spectrum than the 4FGL-DR4 value
of 2.44 +/- 0.03. In addition, two high-energy photons of 13 GeV and 23
GeV are spatially consistent with this blazar at a confidence level p >
0.999. The Fermi-LAT collaboration has previously reported gamma-ray flaring
activity positionally consistent with this source in ATels #17181, #17394,
and #17573.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of this source will continue. This source has been added to
the "LAT Monitored Sources" and, consequently, a preliminary estimation
of the daily gamma-ray flux observed by Fermi-LAT is publicly available
at <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/OI_280>OI
280</a>. A preliminary light curve for OI 280 can be accessed via the Fermi-LAT
Light-Curve Repository at <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J0750.8+1229">4FGL
J0750.8+1229 </a>.  We encourage multifrequency observations of this source.
For this source, the Fermi-LAT contact person is Sarah Wagner (sarah.wagner@uni-
wuerzburg.de).

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.

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https://www.astronomerstelegram.org/?read=17731
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