EP-FXT detection of a new X-ray source EP J005146.9-730930 in the SMC

ATel #16795; Y. J. Xu, Y. Chen, M. Y. Ge, S. M. Jia, C. K. Li, W. W. Cui, D. W. Han, X. F. Zhao, L. M. Song, J. Zhang, J. Guan, H. S. Zhao, J. J. Xu, H. Feng, S. N. Zhang (IHEP, CAS), W. D. Zhang, D. Y. Li, Y. Liu, Z. X. Ling, C. C. Jin, W. Yuan, C. Zhang (NAOC, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau, P. Friedrich, N. Meidinger, V. Burwitz (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team
on 31 Aug 2024; 14:38 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

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We report on the detection of an uncatalogued X-ray source, EP J005146.9-730930, in the SMC by Einstein Probe (EP). The source was detected by the Follow-up X-ray Telescope (FXT) on board EP in a single pointing observation with an exposure time of 2.6 ks, beginning at 2024-08-29T18:49:56 (UTC). The position of the source is R.A. = 12.9435 deg, Dec. = -73.1576 deg, with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). No previously known X-ray source is found in the ROSAT All-sky Survey Source Catalogue (Boller et al. 2016) , the SMC XMM Point Source Catalogue (Sturm et al. 2013), or the first year Swift S-Cubed Survey Catalogue (Kennea et al. 2018) within this error region. An optically bright CV SV* HV 1541 is found with an angular separation of 11.82 arcsec away from the source, based on Simbad.

EP J005146.9-730930 was first detected by EP-FXT on July 25th, when the X-ray flux in the 0.5-10 keV band was only 6.1 (+1.6, -1.6) x 10^(-13) ergs/cm^2/s. This source significantly brightened when observed by FXT later on August 2nd and 15th, as a part of the EP-FXT monitoring observations of the SMC. Preliminary analysis shows that the FXT spectra taken on August 2nd, 15th and 29th can be modeled with an absorbed power-law model with a photon index of 1.2 (+0.2, -0.2), 1.0 (+0.1, -0.1) and 0.9 (+0.1, -0.1), and a column density of 4.5 (+1.0, -0.9) x 10^21, 2.4 (+0.4, -0.4) x 10^21 and 3.2 (+0.8, -0.7) x 10^21 cm^-2, respectively; the derived 0.5-10 keV flux is 1.1 (+0.2, -0.1) x 10^(-11), 3.5 (+0.3, -0.3) x 10^(-11), 1.8 (+0.3, -0.3) x 10^(-11) ergs/cm^2/s, respectively. No significant periodicity is found from quick analysis of the FXT data. Follow-up observations are encouraged to identify the nature of this source.

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.