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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17584, 17585
Message-Id: <20260109071202.39C5C28809DD@server.astronomerstelegram.org>
Date: Fri,  9 Jan 2026 02:12:02 -0500 (EST)

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Posted: Within the last 24 hours
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ATEL #17584							     ATEL #17584

Title:	Fermi-LAT detection of renewed gamma-ray activity from the
		flat-spectrum radio source TXS 2138+527
Author:	Chiara Bartolini (University of Trento &amp; INFN Bari) on
		behalf of the Fermi Large Area Telescope Collaboration
Queries:	chiara.bartolini-1@unitn.it
Posted:	8 Jan 2026; 07:29 UT
Subjects:Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar

The Large Area Telescope (LAT), one of the two instruments on the Fermi
Gamma-ray Space Telescope, has observed gamma-ray emission from a source
positionally consistent with the flat-spectrum radio source TXS 2138+527,
with radio coordinates R.A. = 324.97344 deg, Dec. = 53.00461 deg (J2000;
Immer et al. 2011, ApJS, 194, 25), and unknown redshift. This source is
not yet in any published LAT catalog and was not detected by AGILE or EGRET,
but was already observed in the past by the LAT (ATel #16760).

Preliminary analysis indicates that this source was significantly detected
(>5 sigma) in a high gamma-ray state on 2026 January 6, with a daily averaged
gamma-ray flux (E>100MeV) of (1.3+/-0.2) X 10^-6 photons cm^-2 s^-1 and
a single power-law photon index of 2.1+/-0.1 (statistical uncertainties
only). The level of flaring activity seen on January 6 is the highest LAT
daily flux ever observed for TXS 2138+527.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of TXS 2138+527 will continue and the source will be added to
the list of daily monitored LAT sources, thus providing a preliminary light
curve. We encourage multifrequency observations of this source. The Fermi-LAT
contact person for TXS 2138+527 is C. C. Cheung (chi.c.cheung2.civ at us.navy.mil).

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: Chiara Bartolini (chiara.bartolini-1@unitn.it)
https://www.astronomerstelegram.org/?read=17584
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ATEL #17585							     ATEL #17585

Title:	SVOM/ECLAIRs detection of Cyg X-3 in a likely ultrasoft state
Author:	P.-O. Petrucci (IPAG, France), F. Cangemi (APC, F), A. Coleiro
		(APC, F), S. Guillot (IRAP, F), L. Tao (IHEP, China), L. Zhang (IHEP,
		C)
Queries:	pierre-olivier.petrucci@univ-grenoble-alpes.fr
Posted:	8 Jan 2026; 08:58 UT
Subjects:X-ray, Binary

We report an increase in the X-ray flux of the microquasar Cyg X-3, detected
by the ECLAIRs coded-mask instrument onboard the SVOM mission.  The source
was detected by the Xband quicklook analysis of observations acquired on
January 5th, 2026 after 398 s of exposure with a SNR of 47 in the 4-10
keV energy range.

The ECLAIRs long-term lightcurve showed a spectral softening of the source
which started in Nov./Dec. 2025. The 4-40 keV spectrum obtained on January
5th, 2026 is well described by a diskbb model (chi2/dof = 11.80/13), with
an inner disk temperature of kT = 1.42 +/- 0.07 keV (90% confidence range)
and a 4-0 keV flux of (6.3 +/- 0.3)e-9 erg/cm^2/s (90% confidence range).
The spectral analysis of the November 4th, 2025 observation shows that
the spectrum is well described (chi2/dof = 11.11/9) by an absorbed cutoff
power-law model, with a photon index of Gamma = -0.06 +/- 0.74, an energy
cutoff of Ecut = 8 (+4) (-2) keV and a hydrogen column density fixed at
NH = 8.7e22 cm^2 (Cangemi et al. 2021), yielding a 4-40 keV flux of (5.7
+/- 0.6)e-9 erg/cm^2/s. An iron emission line is also detected in the spectrum,
with a centroid energy of 6.4 (+0.3)  (-0.8) keV and a line width of 0.4
(+0.8) (-0.3) keV. This clearly indicates that the source underwent a spectral
state transition starting from this date and persisting up to the present
time.

The current ultrasoft X-ray state is independently confirmed by the MAXI
lightcurves (<a href="https://maxi.riken.jp/star_data/J2032+409/J2032+409_00055058g_lc_all.gif">Link</a>).

Cyg X-3 recurrently enters an ultrasoft X-ray state that can last for few
weeks, marked by a dominant thermal disk below a few keV and suppressed
hard X-rays, often with quenched radio emission. These states, linked to
high accretion rates, typically precede major radio flares, connecting
disk transitions to powerful jet ejections.

Further multiwavelength follow-up observations are encouraged.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission
led by the Chinese National Space Administration (CNSA, China), National
Center for Space Studies (CNES, France) and the Chinese Academy of Sciences
(CAS, China), which is dedicated to observing gamma-ray bursts and other
transient phenomena in the energetic universe. ECLAIRs was developed jointly
by APC, CEA, CNES and IRAP.

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Password Certification: Floriane Cangemi (cangemi@apc.in2p3.fr)
https://www.astronomerstelegram.org/?read=17585
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