TITLE:   GCN CIRCULAR
NUMBER:  37551
SUBJECT: EP240918a: Swift-XRT observation
DATE:    24/09/19 03:02:42 GMT
FROM:    Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>

J. Quirola-Vasquez (Radboud Univ.), P. G. Jonker (Radboud Univ), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), A. J. Levan (Radboud Univ. & Warwick Univ.), F. E. Bauer (PUC), J. van Dalen (Radboud Univ.), M. E. Ravasio (Radboud Univ.), D. Mata Sanchez (IAC), M. A. P. Torres (IAC) report on behalf of a larger collaboration:

We observed the location of the X-ray counterpart of the fast X-ray transient EP240918a reported by the Einstein Probe WXT instrument and FXT (Zhang et al. GCN 37541) using the Swift-XRT Observatory target of opportunity (ObsID: 00016827001). The observation started at 2024-09-18T22:05:49 UT, (i.e. ~10.7 hrs after the X-ray trigger) and lasted for ~1 ksec. The XRT PC mode was used. We do not detect an X-ray counterpart to the transient. The Swift automatic analysis (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8) results in an upper limit of ~1.5E-2 cnt/s. Assuming an absorbed power law model with photon index 1.5 and column density 2.0E20 cm-2, we obtain a flux upper limit of <6.9E-13 erg cm-2 s-1 (0.3-10 keV).

We thank the Neil Gehrels Swift Observatory team for making the X-ray observation possible.