TITLE: GCN CIRCULAR NUMBER: 39739 SUBJECT: GRB 250314A: EP-FXT afterglow detection DATE: 25/03/15 16:32:44 GMT FROM: Damien Turpin at CEA-Saclay dturpin-astro@hotmail.com
D. Turpin, B. Cordier (CEA), H. Q. Cheng, H. N. Yang (NAO, CAS), P. Y. Han (WHU), W. Yuan (NAO, CAS) Y. Wang (PMO, CAS), Rui-Zhi Li (YNAO, CAS) on behalf of the SVOM and Einstein Probe teams
We performed a follow-up observation of GRB 250314A (Wang et al., GCN 39719) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-03-14 21:48:20 (T-TGRB ~ 8.9 hr) for about 1.1ks of exposure in total.
A fading uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position (J2000) RA, DEC = 201.3007, -5.2822 (error=10", 90% C.L.), 1.8 arcminute away from the SVOM/ECLAIRs position (Wang et al., GCN 39719). This position is consistent with the infrared afterglow candidate detected by the NOT and VLT/X-shooter (Malesani et al. GCN 39727; GCN 39732) and the Swift-XRT afterglow candidate source 1 (Kennea et al., GCN 39734).
The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 2.8 x 10^21 cm^-2 and a photon index of ~2.4. The derived average unabsorbed 0.5-10 keV flux is 5.2 (-/+1.6) x 10^(-13) erg/s/cm^2. Compared to the Swift-XRT epoch (Kennea et al., GCN 39734), the flux of the source 1 has shown a significant fading. We thus conclude this source is indeed the x-ray afterglow of GRB 250314A.
Further observations of the GRB 250314A are planned with EP-FXT.
The above observation was made with the EP-FXT instrument. 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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