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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17377, 17378
Message-Id: <20250909071120.2F5602880992@server.astronomerstelegram.org>
Date: Tue,  9 Sep 2025 03:11:20 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17377							     ATEL #17377

Title:	Einstein Probe detection of a new bright outburst from GRS
		1739-278
Author:	Y. H. Cheng (SWIFAR, YNU), C. Zhou (HUST), S. L. Wang (YNU),
		T. Y. Liu, H. Q. Cheng, C. C. Jin (NAO, CAS) 
Queries:	ep_ta@bao.ac.cn
Posted:	8 Sep 2025; 09:33 UT
Subjects:X-ray, Binary, Black Hole

We report on the detection of a new bright X-ray outburst from the black
hole low-mass X-ray binary candidate GRS 1739-278, by the Wide-field X-ray
Telescope (WXT) on board the Einstein Probe (EP) mission. A previous outburst
of GRS 1739-278 was observed from mid June to mid August 2025 (ATel #17238),
with the peak flux of ~1e-9 erg/s/cm^2. Later the source went into a new,
brighter outburst. The spectrum of the latest WXT observation (started
on 2025-09-07T22:45:57 UTC) can be generally fitted by an absorbed multi-color
disk blackbody model (tbabs*diskbb), with a neutral hydrogen column density
of 1.7(+/-0.05) x 10^22 cm^-2 and temperature of the inner radius of 0.92(+/-0.03)
keV. The derived observed flux in 0.5-4 keV is 4.0(+/-0.9) x 10^-9 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).

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Password Certification: Yuan Liu (liuyuan@bao.ac.cn)
https://www.astronomerstelegram.org/?read=17377
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ATEL #17378							     ATEL #17378

Title:	Fermi-LAT detection of renewed gamma-ray activity from the
		FSRQs 4C +27.50 and PKS 1440-389
Author:	P. van Zyl (South African Radio Astronomy Observatory) and
		F. Longo (University of Trieste and INFN Trieste) on behalf of the
		Fermi Large Area Telescope Collaboration
Queries:	pfesi24@gmail.com
Posted:	8 Sep 2025; 18:32 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 4C
+27.50, also known as 4FGL J2321.9+2734 (4FGL-DR4), with coordinates R.A.
= 350.49943 deg, Dec. = 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 September 7, 2025,  with a daily averaged gamma-ray flux
(E>100MeV) of (1.2+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty
only). This corresponds to a flux increase by a factor of about 60 times,
relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL-DR4,
Ballet et al. 2024, arXiv:2307.12546). The corresponding photon index is
2.3+/-0.2, indicating a significantly harder spectrum than the 4FGL-DR4
value of 2.6+/-0.1. The Fermi LAT Collaboration has previously reported
flaring activity from this source in ATels #17055, #17035, #16718, #15746
and #15549.

The Fermi LAT has also observed renewed gamma-ray activity from a source
positionally consistent with the flat-spectrum radio quasar PKS 1440-389,
also known as 4FGL J1443.9-3908 (Abdollahi, et al. 2020, ApJS, 247, 33),
with radio coordinates R.A. = 220.98833 deg, Decl. = -39.14436 deg (J2000;
Healey et al. 2007, ApJS, 171, 61), and redshift z=0.1385 (Goldoni et al.
2021, A&A 650, A106).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on September 7, 2025,  with a daily averaged gamma-ray flux
(E>100MeV) of (0.5+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty
only). This corresponds to a flux increase by a factor of about 20 times,
relative to the average flux reported in 4FGL-DR4. The corresponding photon
index is 2.2+/-0.3, indicating a similar spectrum to the 4FGL-DR4 value
of 2.24+/-0.04. The Fermi LAT Collaboration has previously reported flaring
activity from this source in the ATel #15635.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of this source will continue.  Preliminary Fermi-LAT light curves
can be accessed via the Fermi-LAT Light-Curve Repository for  <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J1443.9-3908">PKS
1440-389</a>. 4C +27.50 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 the <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/4C_p27d50">LAT
daily monitored source list</a>. We encourage multifrequency observations
of these sources. For PKS 1440-389, the Fermi-LAT contact persons are S.
Ciprini (stefano.ciprini[at]ssdc.asi.it) and C.C. Cheung (teddy.cheung[at]nrl.navy.mil),
and for 4C +27.50 is Giovanni La Mura (giovanni.lamura@inaf.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.

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