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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17167, 17168
Message-Id: <20250506071146.3061B28804C2@server.astronomerstelegram.org>
Date: Tue,  6 May 2025 03:11:46 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17167							     ATEL #17167

Title:	 Fermi-LAT detection of renewed gamma-ray activity from OP
		313
Author:	P. V van Zyl (South African Radio Astronomy Observatory, SARAO),
		 P. Monti-Guarnieri (University of Trieste and INFN Trieste)
Queries:	pvanzyl@sarao.ac.za,PIETRO.MONTI-GUARNIERI@phd.units.it
Posted:	5 May 2025; 16:00 UT
Subjects:Gamma Ray, AGN

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 OP
313, also known as 4FGL J1310.5+3221 (The Fermi-LAT collaboration 2020,
ApJS, 247, 33), with coordinates R.A. = 197.61943 deg, Dec. = +32.34549
deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.997 (Schneider
et al. 2010, AJ, 139, 2360).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on May 4, 2025, with a daily averaged gamma-ray flux (E>100MeV)
of (3.8+/-0.3) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only),
about 70 times higher than the average flux reported in the fourth data
release of 4FGL (4FGL-DR4; Ballet et al. 2024, arXiv:2307.12546). This
is the highest LAT daily flux ever observed for this source. The corresponding
photon index is 2.0+/-0.1, indicating a significantly harder spectral state
than the 4FGL-DR4 value of 2.23+/-0.01. The Fermi-LAT Collaboration has
previously reported flaring activity from this source in ATels #6068, #15483,
#16356, #16497, #16940, and #16970.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of this source will continue. Preliminary Fermi-LAT light curves
for OP 313 can be accessed via the Monitored Source List, and via theFermi-LAT
Light-Curve Repository. We encourage multifrequency observations of this
source. For this source, the Fermi-LAT contact person is Sara Buson (sara[DOT]buson[AT]astro[DOT]uni-wuerzburg[DOT]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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Password Certification: Pfesesani van Zyl (pfesi24@gmail.com)
https://www.astronomerstelegram.org/?read=17167
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ATEL #17168							     ATEL #17168

Title:	Einstein Probe detects possible X-ray brightening of the Low-Mass
		X-ray Binary 4U 1246-58
Author:	Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC), H. Y. Liu (NAO, CAS),
		H. L. Peng (NJNU), X. L. Chen(YNU), C. C. Jin (NAO, CAS) report on
		behalf of the Einstein Probe team:
Queries:	ep_ta@bao.ac.cn
Posted:	5 May 2025; 16:59 UT
Subjects:X-ray, Binary

We report the detection of possible X-ray brightening from the low-mass
X-ray binary (LMXB) 4U 1246-58, by the Wide-field X-ray Telescope (WXT)
on board the Einstein Probe (EP) mission. The source exhibited a gradual
flux increase starting in late April 2025, reaching peak brightness during
an observation at 2025-05-01 09:37:15 (UTC).

The WXT spectrum during the peak can be fitted by an absorbed power-law
with a photon index of 2.3 (+0.5/-0.4) and a neutral hydrogen column density
of 5.8 (+1.5/-1.4) x 10^21 cm^-2. The derived absorbed flux in 0.5-4 keV
is 2.2 (+0.4/-0.2) e-10 erg/s/cm^2, which is roughly four times of the
persistent flux level of ~ 5e-11 erg/s/cm^2.

Multi-wavelength follow-up observations are encouraged.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor
the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook
of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy
of Sciences in collaboration with ESA, MPE and CNES.

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Password Certification: Yilong Wang (wangyilong@nao.cas.cn)
https://www.astronomerstelegram.org/?read=17168
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