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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel 17778, 17779
Message-Id: <20260508070534.6FB4828808F0@server.astronomerstelegram.org>
Date: Fri, 8 May 2026 03:05:34 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17778							     ATEL #17778

Title:	LEDA 735555: WISE detection of long-term infrared brightening
		and a flare in 2021
Author:	Patrik Milan Veres (Ruhr-University Bochum)
Queries:	veres@astro.ruhr-uni-bochum.de
Posted:	7 May 2026; 12:46 UT
Subjects:Infra-Red, AGN, Transient

A recent X-ray flare from the galaxy LEDA 735555 detected by Einstein Probe
was reported in ATel #17775, along with a contemporaneous optical brightening.
Another X-ray flare, detected by eROSITA and reported in ATel #17777, showed
an increase in flux by a factor of 9 over the first 1.5 years, then faded.
This flare was also coincident with an optical flare at the position of
AT 2021jbt an optical transient discovered by ATLAS.

We retrieved the WISE infrared light curve of LEDA 735555 using timewise.
This shows a general increasing trend (both in W1 and W2) similar to the
optical Gaia light curve (the transient appears as Gaia21daz in Gaia Alerts).
An infrared flare occurs around the time of the first optical flare and
the eROSITA peak, after which the infrared emission remains enhanced. The
W1-W2 color suggests dust heating following the peak but is still below
the widely used AGN color selection criterion (0.8) in all epochs used
for the mid-infrared selection of AGNs with WISE (about the reliability
and completeness of this selection method see Fig. 6. in Stern et al. 2012).

Further observations especially optical spectroscopic follow-up are encouraged.

Stern, D. et al. 2012 ApJ,753,30

timewise: https://jannisnecker.pages.desy.de/timewise_sup/docs/

Gaia21daz: https://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia21daz/

WISE light curve of LEDA 735555: https://drive.google.com/file/d/1H7RJLlaqRWy3WLBnHZFsbC4TqQ_l2I64/view?usp=sharing
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Password Certification: Patrik Milan Veres (veres@astro.ruhr-uni-bochum.de)
https://www.astronomerstelegram.org/?read=17778
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ATEL #17779							     ATEL #17779

Title:	XRISM/Xtend Transient Search (XTS) detected an X-ray flare
		possibly from X205211.81-570110.3
Author:	S. Takatsuka (UOsaka), M. Mizumoto (UTEF), Y. Kanemaru, Y.
		Omiya, Y. Uchida, T. Yoneyama (JAXA), M. Audard (U. de Geneve), E.
		Behar (Technion), K. Fukushima (TUS), T. Hakamata (UOsaka), S. Inoue
		(Kyoto U.), Y. Ishihara (Chuo U.), C. Kang (Ehime U.), T. Kiyomoto
		(Saitama U.), T. Kohmura (TUS), H. Kuramoto (UOsaka), J. Kurashima
		(U. of Miyazaki), Y. Maeda (JAXA), H. Matsumoto (UOsaka), A. Miyamoto
		(UOsaka), K. Mori (U. of Miyazaki), Y. Motogami (Saitama U.), T. Narita
		(RIKEN), M. Nobukawa (NUE), H. Noda (Tohoku U.), S. Ogawa (TUS), Y.
		Sakamoto (Tohoku U.), M. Shidatsu (Ehime U.), H. Takahashi (Hiroshima
		U.), T. Takagi (Ehime U.), F. Takisawa (Ehime U.), Y. Terada (Saitama
		U., JAXA), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida
		(Kyoto U.), A. Yoshimoto (NWU), M. Yoshimoto (Ehime U.)
Queries:	yoneyama.tomokage@jaxa.jp
Posted:	8 May 2026; 06:43 UT
Subjects:X-ray, Star, Transient

XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray
source XRISM J2052-5701 on 2026-05-02 TT. The source position is determined
to be (R.A., Dec.) = (313.049, -57.017) with a systematic error of &sim;
40 arcsec. The Chandra source X205211.81-570110.3 is located &sim; 7 arcsec
apart from XRISM J2052-5701. A possible optical counterpart is Gaia DR3
6457472682313731840 with a distance of &sim; 140 pc, which is located &sim;
8 arcsec apart from XRISM J2052-5701. The angular separation between the
Gaia source and the Chandra source X205211.81-570110.3 is 0.42 arcsec.

The flare started at 2026-05-02 09:39 TT and reached its peak on 2026-05-02
at around 10:13 TT. The flare exponentially decayed in 2 &times; 103
sec. The peak flux is calculated as 2 &times; 10-13 erg s-1
cm-2. A systematic error of roughly 20% should be taken into
account. The corresponding luminosity is 5 &times; 1029 erg
s-1 by assuming the distance of 140 pc.

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
and their corresponding counterparts in the same field of view.

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Password Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
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