TITLE: GCN CIRCULAR NUMBER: 36827 SUBJECT: EP240703a and EP240703b: Swift/XRT upper limits DATE: 24/07/05 08:51:47 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> Q. C. Shui, J. Q. Peng (IHEP, CAS), C. Y. Dai (NJU), Y. L. Wang, C. C. Jin, Z. X. Ling, W. Yuan, Y. Liu, C. Zhang, H. Q. Cheng, W. Chen, 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, S. X. Wen, Q. Y. Wu, X. P. Xu, 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 transients EP240703a (Wang et al., GCN 36807) and EP240703b (Peng et al., GCN 36810) by the Einstein Probe, we triggered two Swift target of opportunity observations, one for each source. The Swift observation of EP240703a (observation ID: 00016698001) began at 2024-07-03T18:16:06, about 17.5 hours after the WXT detection, with an exposure time of 1845 s in the Photon Counting mode. No significant X-ray source was detected within the 3 arcmin region around the WXT position of EP240703a. Assuming an absorbed power-law model with a Galactic column density of 5.68 × 10^21 cm^-2 and a photon index of 1.0, the estimated flux upper limit in 0.3-10 keV at the 90% confidence level is 1.62 × 10^-13 erg/cm^2/s. The Swift observation of EP240703b (observation ID: 00016699001) began at 2024-07-03T19:58:00, about 14.5 hours after the WXT detection, with an exposure time of 1738 s in the Photon Counting mode. No significant X-ray source was detected within the 3 arcmin region around the WXT position of EP240703b. Assuming an absorbed power-law model with a Galactic column density of 9.52 × 10^20 cm^-2 and a photon index of 1.0, the estimated flux upper limit in 0.3-10 keV at the 90% confidence level is 1.06 × 10^-13 erg/cm^2/s. We thank the Neil Gehrels Swift Observatory team for making the X-ray observations possible. View this GCN Circular online at https://gcn.nasa.gov/circulars/36827. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...