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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17652, 17653, 17655, 17656
Message-Id: <20260209072744.C18482880902@server.astronomerstelegram.org>
Date: Mon,  9 Feb 2026 02:27:44 -0500 (EST)

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Posted: Within the last 24 hours
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ATEL #17652							     ATEL #17652

Title:	LFBOT ATeL#17646: infrared J band photometric observation
Author:	Bin Ma, Hao-ran Zhang Yun Shi, Jin-Ji Li, Pu Lin, Hao-Nan
		Yang, Zhong-Nan Dong, Yan Yu, Jia-Qi Lin, Wei-Sen Huang, Chun Chen,
		Duo-Le Cao, P H Thomas Tam, Rong-Feng Shen (Sun Yat-sen University)
		
Queries:	mabin3@mail.sysu.edu.cn
Posted:	8 Feb 2026; 10:45 UT
Subjects:Infra-Red, Transient

We observed the field of the LFBOT candidate reported by Tsuboi et al.
(ATel #17646) and followed up by Gill et al. (ATel #17647), Pereyra et
al. (ATel #17648), Schneider et al. (ATel #17649) and Sun et al. (ATel
#17651) using the Sun Yat-sen University (SYSU) 80 cm infrared telescope.
The J band observation started at 2026-02-06T14:04 (UTC), with 20s*90 exposures.
We still detect the transient with a preliminary Vega magnitude of J ~
16.5 mag, which is calibrated again the 2MASS catalog. We will continue
to monitor it with SYSU 80 cm telescope. 
The SYSU 80cm infrared telescope is operated and managed by the Department
of Astronomy, Sun Yat-sen University.

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Password Certification: Bin Ma (mabin22@gmail.com)
https://www.astronomerstelegram.org/?read=17652
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ATEL #17653							     ATEL #17653

Title:	Continued Swift Monitoring of the Stellar-mass Black Hole GX
		339-4
Author:	J. M. Miller, I. Chan, I. Dumitrascu, M. Lopez (Univ. of Michigan)
Queries:	jonmm@umich.edu
Posted:	8 Feb 2026; 16:46 UT
Subjects:X-ray, Binary, Black Hole, Transient

GX 339-4 is a stellar-mass black hole that has recently been observed 
in a hard state outburst (ATEL #17484).  We report on the most recent X-ray

monitoring observation with the Neil Gehrels Swift Observatory.  ObsID

00016552122 started on February 4, 2026, at 08:03:07 UTC.  A total 
exposure of 640 seconds was obtained using the XRT, operated in 
"windowed timing" mode.  We derived a spectrum and response files in 
the standard manner, grouped the data to require at least 15 counts 
per bin, and made simple fits across the 0.7-10.0 keV band using XSPEC.

Fits to the spectrum with an absorbed power-law model give a column 
density of N_H = 6 +/- 1 E+21 cm^-2, a photon index of Gamma = 1.4 +/-

0.1, and a normalization of 2.1 +/- 0.3 E-3 ph/cm^2/s/keV at 1 keV. 
This translates to an absorbed flux of 1.6 +/- 0.2 E-10 erg/cm^2/s 
(0.5-10.0 keV), or an unabsorbed flux of 1.9 E-10 erg/cm^2/s. 
Assuming a distance of 8 kpc, this corresponds to a luminosity of L = 
1.5 +/- 0.1 E+36 erg/s.  For a black hole mass of 5.8 solar masses 
(Hynes et al. 2003), this corresponds to an Eddington fraction of 
0.002.

The source continues a slow decay through the low/hard state.

References

Hynes, R., et al., 2003, ApJ, 583, L95

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Password Certification: Jon Miller (jonmm@umich.edu)
https://www.astronomerstelegram.org/?read=17653
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ATEL #17655							     ATEL #17655

Title:	Squash Photometry of Candidate LFBOT AT2026cex
Author:	B. Garton, I. A. Steele (Liverpool JMU, UK)
Queries:	iainsteele@mac.com
Posted:	8 Feb 2026; 21:42 UT
Subjects:Optical, Transient

We were alerted by Atel#17646 to the candidate LFBOT AT2026cex. This formed
an exciting first science target for the in-progress Squash Spectrograph
being tested at the 2.0m Liverpool Telescope on La Palma. We obtained 10x5
second exposures on the night of 2026 February 07 with a clear filter on
the acquisition camera. Calibrated using V-band magnitudes from APASS we
found the candidate to have an apparent magnitude of 17.05+/-0.15. The
object is therefore continuing to fade.

Liverpool Telescope: http://telescope.ljmu.ac.uk/
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Password Certification: Iain Steele (iainsteele@mac.com)
https://www.astronomerstelegram.org/?read=17655
==============================================================================
ATEL #17656							     ATEL #17656

Title:	Candidate LFBOT AT2026cex: TNT Optical Observations
Author:	Lin Lin (BNU), Jianghua Wu (BNU), Yilin Li (BNU)
Queries:	llin@bnu.edu.cn
Posted:	9 Feb 2026; 02:11 UT
Subjects:Optical, Transient

We observed the field of the candidate LFBOT reported by Tsuboi, Nakaoka,

& Kawabata (ATeL #17646) with the 80cm Tsinghua-NAOC Telescope (TNT, http://www.xinglong-naoc.cn/html/gcyq/80/detail-27.html)
at the Xinglong Observatory of the National Astronomical Observatories
of China on 2026 February 6.

TNT imaged the position in B, V and R bands. The data were analysed 
with AstroImageJ. We detect the transient with the following magnitudes:

B = 16.61 +/- 0.04 at 11:01 UT with a 300s exposure  
V = 16.50 +/- 0.04 at 11:06 UT with a 300s exposure  
R = 16.46 +/- 0.04 at 11:11 UT with a 300s exposure

B = 16.84 +/- 0.04 at 15:48 UT with a 300s exposure  
V = 16.59 +/- 0.04 at 15:53 UT with a 300s exposure  
R = 16.65 +/- 0.04 at 15:58 UT with a 300s exposure

We thank the staff of the Xinglong Observatory.

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Password Certification: Lin Lin (llin@bnu.edu.cn)
https://www.astronomerstelegram.org/?read=17656
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