TITLE: GCN CIRCULAR NUMBER: 40040 SUBJECT: GRB 250402A: EP-FXT afterglow detection DATE: 25/04/04 09:08:48 GMT FROM: Damien Turpin at CEA-Saclay dturpin-astro@hotmail.com
D. Turpin, B. Cordier (CEA), H. Q. Cheng (NAO, CAS), R.-Z. Li (YNAO, CAS), Q. C. Zhao, Z. H. Yang (IHEP, CAS), Y. Liu (NAO, CAS), W. Yuan (NAO, CAS) on behalf of the SVOM and Einstein Probe teams
We performed a follow-up observation of GRB 250402A (Chen et al., GCN 40014) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-04-03 20:30:51 (T-TGRB ~ 21.4 hr) for about 4.6ks of exposure in total.
A bright uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position (J2000) RA, DEC = 213.4094, -5.9295 (error=10", 90% C.L.), 2.1 arcminute away from the SVOM/ECLAIRs position (Chen et al., GCN 40014). This position is consistent with the x-ray and optical afterglow positions reported by SVOM/VT (Xin et al., GCN 40015), SVOM/MXT (Maggi et al., GCN 40019), the LCO telescope (Pérez-Fournon et al., GCN 40020), VLT/X-shooter (Schneider et al., GCN 40022), SVOM/COLIBRI (FM-GFT, Magnani et al., GCN 40023) and Swift/XRT (Dichiara et al., GCN 40027).
The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.2 x 10^21 cm^-2 and a photon index of 2.16 (-0.22/+0.25). The derived average observed 0.5-10 keV flux is 1.31 (-0.12/+0.16) x 10^(-12) erg/s/cm^2.
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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