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Detection of possible X-ray brightening from the HMXB 4U 2238+60 by Einstein Probe

ATel #16750; T. Y. Lian (NAOC, CAS), H. Zhou (PMO, CAS), H. N. Yang, C. C. Jin, W. Yuan, W. D. Zhang, Z. X. Ling, Y. Liu, C. Zhang, W. Chen, 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, Z. Z. Lv, X. Mao, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, S. X. Wen, Q. Y. Wu, X. P. Xu, Y. F. Xu, M. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, J. Guan, C. K. Li, W. W. Cui, H. Feng, D. W. Han, W. Li, C. Z. Liu, F. J. Lu, L. M. Song, J. Wang, J. J. Xu, J. Zhang, S. N. Zhang, H. S. Zhao, X. F. Zhao, W. W. Cui, X. F. Zhao, J. Zhang, C. K. Li, D. W. Han(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.
on 4 Aug 2024; 10:05 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

Subjects: X-ray, Binary

Referred to by ATel #: 16762, 16800, 16803

We report on the detection of possible brightening of the HMXB 4U 2238+60 in X-ray by the Einstein Probe (EP). The source was first detected by the Wide-field X-ray Telescope (WXT) on board EP at 2024-08-01T02:22:37(UTC) with an exposure time of 11316 s, resulting in an average observed flux of ~ 1.0 x 10^(-11) ergs/cm^2/s.

An observation conducted with the Follow-up X-ray Telescope (FXT) on board EP was performed at 2024-08-03T00:48:51 with an exposure time of 2421 s. A bright X-ray source was detected at R.A.= 339.8390 deg, Dec.= 61.2729 deg (with an uncertainty of 10 arcsec), consistent with the WXT source position. The position is consistent with that of the HMXB 4U 2238+60 with an angular separation of 5.5 arcsec from Gaia EDR3. This source was previously detected by Chandra in 2013, yielding the flux of 3.8(+/-0.4) x 10^(-13) ergs/cm^2/s (0.5-7 keV, at a separation of 5.3"). Preliminary analysis shows that the FXT spectrum can be modeled by an absorbed power law with a photon index of 0.8 (+/-0.2), and the derived unabsorbed 0.5-10 keV flux is 5.4 (+/-0.4) x 10^(-11) ergs/cm^2/s. The uncertainties are given at the 90% confidence level for the above parameters.

The EP detection suggests that 4U 2238+60 is likely brightening in X-ray. Multi-band follow-up observations are encouraged.

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.