GCN Circular 38251
Subject
EP241115a/GRB 241115D: Swift/XRT follow-up observation
Date
2024-11-16T12:07:06Z (11 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C. Y. Dai (NJU),M. Q. Huang, Z. Y. Liu (USTC), Y. J. Zhang (THU), C. X. Zhang (HUST), J. W. Hu, Y. Liu (NAO, CAS) on behalf of the Einstein Probe team
Following up on the new X-ray transient EP241115a detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 38239), which was associated with the GRB 241115D (Wang et al., GCN 38250), we performed a target of opportunity observation with Swift about 24 hours later. The Swift XRT observation began at 2024-11-16 at 06:00:03 (UTC) with an exposure time of 1448 seconds in the Photon Counting mode. An uncatalogued X-ray source was detected at R.A. = 19.4188 deg, DEC = -17.9596 deg (J2000) with an uncertainty of about 4.3 arcsec (radius, 90% C.L. statistical and systematic) and a signal-to-noise (S/N) ratio of 6.98, which is consistent with the position of the WXT transient within the uncertainties. We suggest that this XRT source is most likely associated with EP241115a.
The average XRT spectrum can be fitted with an absorbed power law with a photon index of 1.50(+/-0.38) (with a column density fixed at the Galactic one of 1.6 x 10^20 cm^-2). The derived average unabsorbed 0.3-10 keV flux is 2.1(+0.9/-0.5) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
We thank the Neil Gehrels Swift Observatory team for making the X-ray observation possible.