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The Astronomer's Telegram                   http://www.astronomerstelegram.org

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ATEL #16631							    ATEL #16631

Title:	EP-WXT detected an X-ray flare in the Small Magellanic Cloud
Author:	H. N. Yang, W. Chen, X. Pan, Z. Z. Lv, Z. X. Ling, W. Yuan,
		Y. Liu, C. Zhang, C. C. Jin, H. Q. Cheng, C. Z. Cui, D. W. Fan, H.
		B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, T. Y.
		Lian, X. Mao, H. W. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu,
		X. P. Xu, Y. F. Xu, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang (NAOC,
		CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A.
		Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra,
		A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team
Queries:	ep_ta@bao.ac.cn
Posted:	28 May 2024; 05:50 UT
Subjects:X-ray, Binary, Transient

We report on the detection of an X-ray outburst at 2024-05-27T08:41:28
(UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe
(EP) mission. The source, temporarily designated EP J0052.9-7230, was detected
in two WXT observations from 2024-05-27T08:41:28 to 2024-05-27T12:47:16,
whereas it was not detected in previous observations on May 24 and 25.
The source position, R.A. = 13.215 deg, DEC = -72.494 deg (J2000) with
an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic),
is close to the positions of the known sources SMC X-3 and CXOU J005245.0-722844,
both being HMXB. The measured angular distance between the WXT source and
SMC X-3 ranges from 2.9 to 5.0 arcmin, which is larger than the source
positioning uncertainty for WXT. We thus suggest that the outburst is unlikely
associated with SMC X-3. Whereas the source is only 1 arcmin away from
CXOU J005245.0-722844, therefore it is possible that the outburst is associated
with CXOU J005245.0-722844. If this is the case, the X-ray flux of CXOU
J005245.0-722844 would have increased by about 5 orders of magnitude compared
to its previous flux measured by Chandra. Further observations with better
source localization are encouraged to confirm the suggested identification
of this WXT source.

The averaged 0.5-4 keV spectrum of the WXT source in these two observations
can be fitted with an absorbed black body with a temperature of 0.087 (-0.002,+0.002)
keV and 0.091 (-0.001,0.001) keV (with the column density fixed at the
Galactic value of 4.8 x 10^21 cm^-2), giving an unabsorbed flux of 1.76
(-0.08,+0.08) x 10^-9 erg/s/cm2 and 1.52 (-0.05,+0.05) x 10^-9 erg/s/cm2
in the 0.5-4 keV band, respectively. The 1-sigma uncertainties are given
for the above parameters.

The above observation was made with the WXT instrument during the commissioning
phase of EP. 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). EP is a mission
of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.

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