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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel 17144, 17145, 17146
Message-Id: <20250415071640.3B6AF2880175@server.astronomerstelegram.org>
Date: Tue, 15 Apr 2025 03:16:40 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17144							     ATEL #17144

Title:	XRISM/Xtend Transient Search (XTS) detected an X-ray flare
		from an eclipsing binary
Author:	Y. Ishihara (Chuo U.), K. Fukushima, Y. Kanemaru, S. Ogawa
		(JAXA), M. Audard (U. de Geneve), E. Behar (Technion), S. Inoue (Kyoto
		U.), T. Kohmura (TUS), Y. Maeda (JAXA), M. Mizumoto (UTEF), N. Nagashima
		(Chuo U.), M. Nobukawa (NUE), K. Pottschmidt (UMBC, NASA GSFC, CRESST),
		M. Shidatsu (Ehime U.), H. Sugai (Chuo U.), Y. Terada (Saitama U.),
		Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.),
		T. Yoneyama (Chuo U.), M. Yoshimoto (Ehime U.)
Queries:	tyoneyama263@g.chuo-u.ac.jp
Posted:	14 Apr 2025; 11:24 UT
Subjects:X-ray, Binary, Star, Transient, Variables

XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray
source XRISM J1746-2940 on 2025-04-12 TT. The source position is determined
to be (R.A., Dec.) = (266.528, -29.671), with a systematic error of ~ 40
arcsec. A plausible counterpart is an eclipsing binary V734 Sgr located
~ 10 arcsec apart from the position of XRISM J1746-2940.

The flare started at 2025-04-12 at ~ 12:38 TT. The flare reached its peak
on 2025-04-12 at ~ 13:12. The flare exponentially decayed in 104
sec. 
The peak flux is estimated to be 2 &times; 10-11 erg s-1
cm-2 (0.4 &ndash; 10.0 keV). A systematic error of roughly 20%
should be added to the statistical error. Corresponding luminosity is 2
&times; D978pc<sup2> &times; 1033 erg s-1
by assuming the distance to XRISM J1746-2940 of D978pc.

We derived the above systematic error for the flux by comparing our derived
values for the sources detected with XTS in several observations with those
for the corresponding X-ray counterparts. We estimated the systematic error
for the source position from the separations between the detected sources
with the corresponding counterparts in the same field of view.

------------------------------------------------------------------------------
Password Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
https://www.astronomerstelegram.org/?read=17144
==============================================================================
ATEL #17145							     ATEL #17145

Title:	XRISM/Xtend Transient Search (XTS) detected an outburst from
		a white dwarf candidate
Author:	N. Nagashima  (Chuo U.), K. Fukushima, Y. Kanemaru, S. Ogawa
		(JAXA), M. Audard (U. de Geneve), E. Behar (Technion), S. Inoue (Kyoto
		U.), Y. Ishihara (Chuo U.), T. Kohmura (TUS), Y. Maeda (JAXA), M.
		Mizumoto (UTEF), M. Nobukawa (NUE), K. Pottschmidt (UMBC, NASA GSFC,
		CRESST), M. Shidatsu (Ehime U.), H. Sugai (Chuo U.), Y. Terada (Saitama
		U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto
		U.), T. Yoneyama (Chuo U.), M. Yoshimoto (Ehime U.)
Queries:	tyoneyama263@g.chuo-u.ac.jp
Posted:	14 Apr 2025; 12:02 UT
Subjects:X-ray, Transient, Variables

XRISM/Xtend Transient Search (XTS) detected an X-ray outburst from an X-ray
source XRISM J1826-3651 on 2025-04-12 TT. The source position is determined
to be (R.A., Dec.) = (276.543, -36.849), with a systematic error of ~40
arcsec. A plausible counterpart is a white dwarf candidate Gaia DR3 6728071049507752320,
which is located ~16 arcsec apart from the position of XRISM J1826-3651.

The XRISM observation was started at 2025-04-12T18:07:19 TT, where the
flux was estimated to be 8 &times; 10-14 erg s-1
cm-2 (0.4 &ndash; 10.0 keV). The source flux was increased
by an order of magnitude (8 &times; 10-13 erg s-1
cm-2) by 2025-04-12 at ~22:52 TT. The outburst was continuing
at the end of the observation, 2025-04-13T02:55:13 TT. Corresponding luminosities
were 3 &times; D1.7 kpc2 &times; 1031
erg s-1 and 3 &times; D1.7 kpc2 &times;
1032 erg s-1, respectively by assuming the distance
to XRISM J1826-3651 of D1.7 kpc.

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Password Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
https://www.astronomerstelegram.org/?read=17145
==============================================================================
ATEL #17146							     ATEL #17146

Title:	Fermi-LAT detection of renewed gamma-ray activity from FSRQ
		S4 0805+41
Author:	Federica Giacchino (INFN Roma Tor Vergata &amp; SSDC ASI),
		Giovanni La Mura (INAF-OAC) on behalf of the Fermi Large Area Telescope
		Collaboration
Queries:	federica.giacchino@roma2.infn.it
Posted:	14 Apr 2025; 20:13 UT
Subjects:Gamma Ray, >GeV, AGN, Blazar, 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 the flat spectrum radio quasar
S4 0805+41, also known as 4FGL J0809.3+4053  (4FGL-DR4; Ballet et al. 2024,
arXiv:2307.12546), with radio coordinates R.A. = 122.23605 deg, Decl. =
40.87914 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift
z=1.419 (Xu et al. 1994, AJ, 108, 395; Schneider et al. 2010, AJ, 139,
2360).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on 2025 April 13, with a daily averaged gamma-ray flux (E>100MeV)
of (0.4+/-0.1) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only),
corresponding to a flux increase of a factor of about 40 relative to the
average flux reported in 4FGL-DR4. The photon index is 2.01 +/- 0.22, corresponding
to a significantly harder spectrum than the 4FGL-DR4 catalog value of 2.63
+/- 0.08. The spectral hardening resulted in the detection of one high-energy
(E = 11 GeV) photon, having a probability of being associated with the
source p > 0.999. The Fermi-LAT Collaboration has previously reported enhanced
activity from this source in ATel #15704.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of S4 0805+41 will continue. This source has an entry in the
Fermi LAT light curve repository (https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J0809.3+4053).
We encourage multifrequency observations of this gamma-ray source. For
this source, the Fermi-LAT contact person is C.C. Cheung (teddy.cheung@nrl.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: Federica Giacchino (federica.giacchino@roma2.infn.it)
https://www.astronomerstelegram.org/?read=17146
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