TITLE: GCN CIRCULAR NUMBER: 39456 SUBJECT: GRB 250219A: EP-FXT afterglow detection DATE: 25/02/24 14:43:44 GMT FROM: Damien Turpin at CEA-Saclay dturpin-astro@hotmail.com
D. Turpin (CEA), P. Y. Han, C. X. Zhang (HUST), J. Yang (NJU), X. Tian (GXU), D. F. Hu (PMO, CAS), W. Chen (NAO, CAS), J. Guan, C. K. Li, Y . Chen, S. M. Jia, W. W. Cui, 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 (IHEP , CAS), Y . Liu, C. C. Jin, C. Zhang, Z. X. Ling (NAOC,CAS), B. Cordier (CEA) on behalf of the SVOM and Einstein Probe teams
We performed a follow-up observation of GRB 250219A (Daigne et al., GCN 39376) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-02-21T07:04:16 (T-TGRB ~ 1.63 days) for about 3ks of exposure in total.
An uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position of the x-ray afterglow candidate reported by Swift/XRT (Kennea et al., GCN 39379). This position is also consistent with the optical afterglow detected by SVOM/VT (Xin et al., GCN 39380), COLIBRÍ (Magnani et al. GCN 39382) and the NOT (Fu et al., GCN 39383).
A preliminary analysis shows that the spectrum can be fitted with an absorbed power law with nH=1.53*10^20 cm^-2 and a photon index of 1.53 (-0.68/+0.70) . The observed flux in the 0.3-10.0 keV is 4.4 (+2.2/-1.1)*10^-13 erg/s/cm^2. Compared to the Swift/XRT epoch Kennea et al., GCN 39379), the observed source flux has faded by almost one order of magnitude with a temporal slope alpha~-0.56.
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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