TITLE:   GCN CIRCULAR
NUMBER:  36808
SUBJECT: EP240702a: Swift/XRT upper limit
DATE:    24/07/03 13:31:10 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

W. Chen, X. P. Xu (NAOC, CAS), C. Y. Dai (NJU), S. X. Wen, Z. X. Ling, W. Yuan, Y. Liu, C. Zhang, C. C. Jin, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team

Following the detection of the fast X-ray transient EP240702a by the Einstein Probe (Chen et al., GCN 36801), we performed a Swift target of opportunity observation (ObsID: 00016693001). The XRT onboard Swift began the observation at 2024-07-02T09:03:28 UTC, about 8 hours after the WXT detection, with an exposure time of 1950 s in the Photon Counting mode. 

No significant X-ray source was detected within the 3 arcmin region around the WXT position. Assuming an absorbed power-law model with a Galactic column density of 2.0 x 10^20 cm^-2 and a photon index of 1.1, the estimated flux upper limit in 0.3-10 keV at the 90% confidence level is 1.58 x 10^-13 ergs/cm^2/s.

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