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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17304, 17305
Message-Id: <20250725071116.BD83428807A4@server.astronomerstelegram.org>
Date: Fri, 25 Jul 2025 03:11:16 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17304							     ATEL #17304

Title:	ASASSN-25db: A Deep Ongoing Dimming Event 
Author:	D. M. Rowan, K. Z. Stanek, C. S. Kochanek,  B. JoHantgen,
		J. Callahan, S. A. Petz (OSU),  H. Barker (Rutherford Street Observatory),
		B. J. Shappee (Univ. of Hawaii)
Queries:	stanek.32@osu.edu
Posted:	24 Jul 2025; 14:13 UT
Subjects:Optical, Variables

Using data from the All-Sky Automated Survey for SuperNovae (ASAS-SN, <a
href=https://ui.adsabs.harvard.edu/abs/2014ApJ...788...48S/abstract>Shappee
et al. 2014,</A> <a href=https://ui.adsabs.harvard.edu/abs/2017PASP..129j4502K/abstract>Kochanek
et al. 2017,</a> <a href=https://ui.adsabs.harvard.edu/abs/2023arXiv230403791H/abstract>Hart
et al. 2023 </a>), we identified a star with a deep, ongoing, dimming event.
<a href=https://asas-sn.osu.edu/sky-patrol/coordinate/a73dcf89-8cd1-433c-bcc7-4334ca7506c3>ASASSN-25db</A>
(RA = 17h18m33.14s, DEC = -32d06m30.96s, G = 12.7, BP = 13.1, RP =11.5,
DR3 source_id = 5979603728993854720 is a red giant star with a Gaia DR3
(<a href=https://ui.adsabs.harvard.edu/abs/2023A%26A...674A...1G/abstract>Gaia
Collaboration et al. 2023 </a>) extinction-corrected absolute magnitude
M_G = 3.2 mag and color G<sub>BP</sub>&nbsp;-G<sub>RP</sub> = 1.3 mag,
but we note that the fractional Gaia parallax uncertainty is large (~40%).

This star was first observed by ASAS-SN on UT 2016-03-09 and it has roughly
~ 5,700 data points at this time. It had a mean g-magnitude of ~13.0 (V
~ 12.7) and no <a href=https://asas-sn.osu.edu/sky-patrol/coordinate/33ce1348-4c0f-4e62-af3e-40af2bce3f59>previous
dimming events</A>. The dimming event began around UT 2025-05-20. The star
faded by about 0.75 mag in the g-band and began to brighten again on UT
2025-07-17. An R ~ 1000 spectrum taken with a 250mm Newtonian and Shelyak
LISA spectrograph on UT 2025-07-20 shows Na D absorption and H-alpha emission.
There is also an apparent infrared excess in the WISE W3 and W4 bands (<a
href=https://ui.adsabs.harvard.edu/abs/2014yCat.2328....0C/abstract>Cutri
et al. 2021</a>).

We thank Las Cumbres Observatory and its staff for their continued support
of ASAS-SN. ASAS-SN operations are funded in part by the Gordon and Betty
Moore Foundation through grants GBMF5490 and GBMF10501 to the Ohio State
University, and Alfred P. Sloan Foundation grant G-2021-14192.

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Password Certification: Krzysztof  Stanek (stanek.32@osu.edu)
https://www.astronomerstelegram.org/?read=17304
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ATEL #17305							     ATEL #17305

Title:	SVOM J195836+32283 is not a real source
Author:	D. Gotz (CEA), P. Maggi (ObAS)
Queries:	diego.gotz@cea.fr
Posted:	24 Jul 2025; 15:43 UT
Subjects:X-ray, A Comment

A careful re-analysis of the entire MXT data set of the field of SVOM J195836+32283,
including a SVOM follow-up ToO observation, started on July 22nd 2025 at
11:26:07 U.T. for a net exposure of 7 ks, indicates that the new transient
source SVOM J195836+32283, announced in Atel #17297, is in reality an artifact
due to single reflection photons induced by the bright X-ray source Cyg
X-1, which lies at 2.7 degrees from the source position, outside the MXT
field of view.

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Password Certification: Diego Gotz (diego.gotz@cea.fr)
https://www.astronomerstelegram.org/?read=17305
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