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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17926
Message-Id: <20260726070321.03E27288081A@server.astronomerstelegram.org>
Date: Sun, 26 Jul 2026 03:03:21 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17926							     ATEL #17926

Title:	EP J194531.8-612009: Einstein Probe detection of a new X-ray
		transient associated with a Cataclysmic Variable
Author:	X. H. Tang (THU), K. R. Ni (CCNU), Y. J. Zhang (PKU), H. Sun
		(NAOC) on behalf of the Einstein Probe (EP) team
Queries:	ep_ta@bao.ac.cn
Posted:	25 Jul 2026; 14:37 UT
Subjects:X-ray, Cataclysmic Variable, Transient

We report the discovery of a new X-ray transient, EP J194531.8-612009,
identified in the EP-WXT stacked data at RA = 296.419 deg, Dec =-61.318
deg, with an uncertainty of 2.2 arcmin in radius (90%, C.L statistical
and systematic ). No known historical X-ray source is within the WXT error
circle. The 0.5-4 keV flux estimated from the WXT stacked data is approximately
9.2x10^-13 erg/s/cm^2.

A follow-up observation with EP-FXT was carried out on 2026-07-25T03:40:13
(UTC) with an exposure of 1.9 ks, an X-ray source was detected within the
WXT error circle at RA = 296.3825 deg, Dec =-61.3361 deg (uncertainty 10
arcsec, C.L statistical and systematic). The FXT light curve shows no significant
variability. The X-ray spectrum can be fitted with an absorbed power law
with absorption fixed at the Galactic value (N_H = 4.5 x 10^20 cm^-2) and
a photon index of 1.40 (-0.15, +0.16). The unabsorbed 0.5-10 keV flux is
3.70 (-0.55, +0.60) x 10^-12 erg/s/cm^2. The eROSITA-DE gives a 0.2-2.3
keV flux upper limit of 8.5 x 10^-14 erg/s/cm2 at this position (from the
eROSITA-DE upper limit server, Tubín-Arenas et al. 2024; Merloni et al.
2024).

The position of FXT detection is consistent with that of the optical transient
MASTER OT J194531.90-612009.5 (Balanutsa et al., ATel #8036), which is
also identified as a Cataclysmic Variable (CV) in Gaia DR3 6442291862707764096
(Gaia Collaboration, 2022). Thus the X-ray transient is likely the outburst
of the CV. The measured 0.5-10 keV flux corresponds to an X-ray luminosity
of about 3.2 x 10^32 erg/s.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor
the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook
of X-ray and Gamma-ray Astrophysics).

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