TITLE: GCN CIRCULAR NUMBER: 37653 SUBJECT: EP240930a: EP-FXT follow-up observation update DATE: 24/10/01 13:14:13 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
H. L. Peng (NNU), X. Tian (GXU), X. Mao, C. C. Jin, H. Y. Liu, Y. Liu, Z. X. Ling, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, J. W., Hu, M. H. Huang, D. Y. Li, M. J. Liu, Z. Z. Lv, T. Y. Lian, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, X. P. Xu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. D. 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), Y F. Liang (PMO, 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
Following the detection of the fast X-ray transient EP240930a (Tian et al., GCN 37648), we performed an observation of EP240930a with the Follow-up X-ray Telescope (FXT) on board Einstein Probe. The observation began at 2024-10-01T07:06:01 (UTC), about 14 hours after the EP-WXT detection, with an exposure time of 2801 seconds. An uncatalogued source was detected within the WXT positional uncertainty of EP240930a, at R.A. = 319.9331 deg and DEC = 41.3002 deg with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The spectrum can be fitted with an absorbed power-law model with NH fixed at the Galactic value of 3.29E21 cm^-2 and a photon index of 2.1(-0.4, +0.4). The derived average unabsorbed flux in 0.5-10 keV is 7.6(-1.3, +1.7)E-13 erg/s/cm^2 (90% C.L.). We consider this FXT source to be the afterglow of the X-ray transient EP240930a, which is likely associated with the Fermi GRB 240930B (Fermi GBM team, GCN 37640) as proposed in the last circular (Tian et al., GCN 37648).
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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