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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17221, 17222, 17223
Message-Id: <20250606071525.3EF9C288093E@server.astronomerstelegram.org>
Date: Fri,  6 Jun 2025 03:15:25 -0400 (EDT)

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ATEL #17221							     ATEL #17221

Title:	Prolonged X-ray activity of IGR J17091-3624
Author:	Sian A. Woahene-Demehin (University of Southampton), Federico
		M. Vincentelli (INAF-IAPS), Diego Altamirano (University of Southampton),
		Douglas Buisson (Independent), A. Sanna (University of Cagliari),
		James F. Steiner (SAO), K. C. Gendreau, Zaven Arzoumanian (NASA GSFC),
		Gaurava K. Jaisawal (DTU Space), Ole Koenig (CfA). G. Mastroserio
		(IUSS Pavia)
Queries:	swd1g20@soton.ac.uk
Posted:	5 Jun 2025; 09:49 UT
Subjects:X-ray, Binary, Black Hole

IGR J17091-3624 (IGR J17091) is a transient stellar-mass black hole X-ray
binary discovered in 2003. It is well known for its recurrent outbursts
and sporadic highly structured X-ray variability similar to GRS 1915+105
(Altamirano et al. 2011, ApJL, 742, L17; Court et al. 2017, MNRAS, 468,
4748; Wang et al., ApJ 963, 14, 2024). The most recent outburst began in
early February 2025 (ATel #17034, #17038).

Recent optical observations reported a decrease in the optical flux from
a magnitude of  r'=19.48 +/- 0.04 to a magnitude of r'=20.69 +/- 0.12 between
2025-04-1 and 2025-04-28, indicating that the source had entered into a
quiescent phase (ATel #17166).

NICER has been monitoring IGR J17091 since the beginning of the outburst.
Triggered by the optical results reported in Atel #17166, we analyzed the
NICER observations of IGR J17091 taken between 2025-04-18 19:16:20 TT and
2025-05-17 23:37:00 TT with a total exposure of ~25 ks.

IGR J17091 was significantly detected in all our observations, revealing
that although the optical flux is consistent with quiescence levels, IGR
J17091 is declining but still in outburst in X-rays. The 0.5-10 keV light
curve reveals substantial variability, with average count rates changing
between 18 cts/sec and 12 cts/sec over a period of ~2 days. The most recent
observations conducted between 2025-05-15 20:41:20 TT and 2025-05-17 23:37:00
TT reveal an average count rate between 3 and 7 cts/sec.

NICER will continue to monitor IGR J17091, and we encourage further multiwavelength
observations of this source. NICER is an X-ray telescope operating on the
International Space Station, devoted to time-resolved spectroscopy in the
0.2-12 keV band. The NICER mission and portions of the NICER science team
activities are funded by NASA.

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Password Certification: Diego Altamirano (d.altamirano@soton.ac.uk)
https://www.astronomerstelegram.org/?read=17221
==============================================================================
ATEL #17222							     ATEL #17222

Title:	Fermi-LAT detection of enhanced gamma-ray activity from the
		FSRQ TXS 0724+571
Author:	S. Wagner (University of Wuerzburg) and Pietro Monti-Guarnieri
		(University of Trieste) on behalf of the Fermi Large Area Telescope
		Collaboration
Queries:	sarah.wagner@physik.uni-wuerzburg.de
Posted:	5 Jun 2025; 19:33 UT
Subjects:Gamma Ray, >GeV, AGN, Blazar

The Large Area Telescope (LAT), one of the two instruments on the Fermi
Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from
a source positionally consistent with the flat-spectrum radio quasar TXS
0724+571, also known as 4FGL J0729.1+5703 (Abdollahi et al. 2022, ApJS,
260, 53), with coordinates R.A. = 112.20680 deg, Dec. = +57.02344 deg (J2000;
Xu et al. 2019, ApJS, 242, 5), and redshift z = 0.426 +/- 0.001 (Henstock
et al. 1997, MNRAS, 290, 380–400).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on June 4, 2025, 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).
This corresponds to a flux increase of a factor of 150 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 +/- 0.2, indicating a significantly harder spectrum than the
4FGL value of 2.33 +/- 0.13.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of this source will continue. A preliminary light curve for
TXS 0724+571 can be accessed via the <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J0729.1+5703">Fermi-LAT
Light-Curve Repository</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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Password Certification: Sarah Wagner (sarah.wagner@physik.uni-wuerzburg.de)
https://www.astronomerstelegram.org/?read=17222
==============================================================================
ATEL #17223							     ATEL #17223

Title:	Spectroscopic Classification of Astrophysical Transients with
		the Lick Shane Telescope
Author:	R. Kaur, K. C. Patra, K. W. Davis, R. J. Foley (UCSC)
Queries:	kcpatra@ucsc.edu
Posted:	6 Jun 2025; 03:41 UT
Subjects:Optical, Supernovae, Transient

We report the classifications of astrophysical transients from spectroscopic
observations with the Kast spectrograph on the Shane telescope obtained
on 2025 June 03 UT. The targets were supplied by the Young Supernova Experiment
and ATLAS. Targets were identified using the target management platform
YSE-PZ (Coulter et al., 2023, PASP, 135, 4501). The classifications were
performed with SNID (Blondin & Tonry, 2007, ApJ, 666, 1024).

PS25bze      | AT2025jar  | 15:13:53.76  | +00:17:19.77 | 0.071 | Ia-91bg
| +18d  | (1) 
ATLAS25fvu   | AT2025msx  | 11:57:17.69  | +25:11:14.75 | 0.014 | Ic-BL
|  +8d  | (2)

Notes: 
When the redshift is given to 2 decimal places, it is derived from the
SN spectrum. Otherwise, the redshift is determined from the host galaxy.

(1) We measure a redshift of 0.0713 from a spectrum of the host galaxy,
which differs from the NED-listed redshift that was inferred from a friends-of-friends
procedure.  The spectrum matches well with SN 1991bg-like SNe Ia at a phase
of about 18 days after peak at a redshift of 0.07, consistent with our
spectroscopic redshift measurement. We measure a Si II 6355 velocity of
-8,100 km/s.  
(2) The observed spectrum is particularly red, and assuming a typical blue
spectrum for a young SN, the color can be attributed to dust reddening
of E(B-V) ~ 1.2 mag.  The spectrum has broad spectral features consistent
with that of a SN Ic-BL soon after peak brightness.  The ATLAS light curve
is either still rising or at peak, and so we caution that the phase reported
is likely biased by ~7 days.  Correcting for the derived reddening and
a Hubble-flow distance accounting for Virgo inflow and the Great Attractor,
we find an absolute magnitude of M_o = -19.0 mag, consistent with a SN
Ic-BL before peak brightness.

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Password Certification: Kishore Patra (kcpatra@ucsc.edu)
https://www.astronomerstelegram.org/?read=17223
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