TITLE:   GCN CIRCULAR
NUMBER:  37090
SUBJECT: The EP-WXT trigger 01709018832 on August 7th is likely a flaring star
DATE:    24/08/07 14:40:33 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

S. Q. Jiang (NAOC, CAS), Y. C. Fu (BNU), J. W. Hu, Z. X. Ling, W. D. Zhang, Y. Liu, C. C. Jin, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, W. W. Cui, D. W. Han, C. K. Li, L. M. Song, X. F. Zhao, J. Zhang, 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

The candidate X-ray transient (RA=2.562, DEC=-2.665) triggered by the Wide-field X-ray Telescope (WXT) on board Einstein Probe (EP) at 06:22:26 UT on August 7th, 2024 (trigger ID: 01709018832) is likely a stellar flare associated with the star Gaia DR3 2445442335531658752.

Following the detection of this fast X-ray transient, we performed an observation of this source with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission. The observation started at 2024-08-07 07:16:03 UTC, about 1 hour after the WXT detection, with a net exposure time of 3.0 ks.

Within the error circle of WXT, an X-ray source was clearly detected at R.A. = 2.5744 deg, DEC = -2.6782 deg, with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT position is 3.5 arcsec away from a known optical source. The source is likely associated with a possible star, Gaia DR3 2445442335531658752, approximately 76 pc in distance. The spectrum can be well fitted with a model comprising two absorbed apec components with a temperature of 1.03 (-0.08/+0.08) keV and 4.49 (-0.76/+1.10) keV with the column density fixed to 0. The flux of the FXT source is 6.51 (-0.51/+0.55) x 10^-12 erg/s/cm^2 in the 0.5-10 keV range. If the WXT and FXT source is indeed associated with the star, the flare reached a peak luminosity of 4.1 x 10^31 erg/s in the 0.5-4 keV range. (The quoted errors of the parameters derived above are at the 90% C.L.). We thus suggest that the X-ray flare detected by WXT is likely from the star.

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.