TITLE: GCN CIRCULAR NUMBER: 40141 SUBJECT: EP250404a: Nanshan 0.43m Telescope optical observatios DATE: 25/04/13 13:41:02 GMT FROM: Abdusamatjan Iskandar at XAO,CAS <abudu@xao.ac.cn> S. Yaqup, J.Z. Liu, A. Iskandar, Y. Zhang, A. Esamdin, C.H. Bai, T.H. Zhong (XAO) report on behalf of optical group of the XAO: We observed the field of the EP250404a (Einstein Probe mission, Trigger ID 01709133918) with the 0.43m telescope at Nanshan Station of Xinjiang Astronomical Observatory (XAO). The observations were started at 2025-04-04T14:54:21(UTC), and obtained a series of gri band images. The optical afterglow (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al, GCN 40064; He et al., GCN 40069; Perez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al, GCN 40073; Taguchi et al., GCN 40074; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Yin et al., GCN 40085; Pankov et al., GCN 40086; Chu Chen et al., GCN 40088 and Chen et al., GCN 40089) was clearly detected at position R.A. = 125.0606 deg, DEC = 35.5282 deg J2000. The preliminary photometric magnitudes are below: Observation Start-Time T-T0(hr) Exposure Filter Mag. Err. 2025-04-04 14:54:21 0.583 060s g 16.914 0.106 2025-04-04 14:55:56 0.604 060s r 16.067 0.076 2025-04-04 14:57:12 0.626 060s i 15.610 0.080 2025-04-04 14:58:29 0.648 060s g 17.090 0.108 2025-04-04 14:59:48 0.669 060s r 16.294 0.072 2025-04-04 15:01:05 0.690 060s i 15.940 0.105 2025-04-04 15:02:22 0.712 060s g 17.484 0.108 2025-04-04 15:03:41 0.734 060s r 16.398 0.071 2025-04-04 15:04:58 0.755 060s i 15.965 0.099 2025-04-04 15:11:08 0.858 120s i 16.388 0.067 2025-04-04 15:13:25 0.897 120s g 17.690 0.106 2025-04-04 15:15:44 0.934 120s r 17.066 0.077 2025-04-04 15:18:01 0.972 120s i 16.496 0.074 2025-04-04 15:20:19 1.011 120s g 17.735 0.096 2025-04-04 15:22:38 1.049 120s r 17.030 0.059 2025-04-04 15:24:54 1.087 120s i 16.736 0.061 2025-04-04 15:27:12 1.126 120s g 18.184 0.105 2025-04-04 15:29:31 1.164 120s r 17.407 0.070 2025-04-04 15:31:48 1.202 120s i 17.033 0.067 2025-04-04 15:34:27 1.247 200s g 18.252 0.090 2025-04-04 15:52:56 1.554 200s r 17.719 0.085 2025-04-04 15:56:33 1.615 200s i 17.332 0.088 2025-04-05 16:00:10 1.676 200s g 18.508 0.116 2025-04-05 16:03:50 1.736 200s r 18.121 0.087 2025-04-05 16:07:27 1.796 200s i 17.742 0.101 2025-04-05 16:11:04 1.857 200s g 18.335 0.093 2025-04-05 16:14:43 1.917 200s r 17.924 0.070 2025-04-05 16:18:19 1.978 200s i 17.569 0.090 2025-04-05 16:25:36 2.099 200s r 18.261 0.081 2025-04-05 16:36:30 2.280 200s r 18.681 0.117 2025-04-05 16:40:06 2.341 200s i 18.319 0.136 2025-04-05 16:43:45 2.402 200s g 18.815 0.129 2025-04-05 16:47:42 2.467 300s g 18.713 0.123 2025-04-05 16:52:59 2.555 300s r 18.799 0.132 2025-04-05 16:58:16 2.643 300s i 17.798 0.094 2025-04-05 17:03:34 2.732 300s g 19.368 0.188 2025-04-05 17:08:52 2.820 300s r 18.608 0.111 The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40141. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...