TITLE: GCN CIRCULAR NUMBER: 40097 SUBJECT: EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14 DATE: 25/04/06 19:33:24 GMT FROM: qiang xi <xiqiang051@gmail.com> Qiang-Xi (UCAS), Yiming-Mao (NAOC), Xinxiang-Sun (NAOC), Ningchen-Sun (NAOC), Junjie-Jin (NAOC), Min-He (NAOC) report: We detected an optical counterpart for the field of EP 250404A using two independent facilities: the 70 cm telescope UCAS-70 and the 35 cm telescope XL-C14. The optical counterpart was observed at the coordinates: **RA = 08h20m14.54s, Dec = +35°31′42.2″.** Stacked imaging of the field has revealed a clear optical transient. The photometric measurements derived from the stacked images are summarized below. In our analysis, the photometry in the Johnson band was calibrated from APASS data converted using the Lupton (2005) equations, while the SDSS band data were calibrated against the SDSS star catalog. The observation time reported corresponds to the median of the individual exposure times. | Median Time (UT) | Telescope | Exposure (s) | Filter | Magnitude | Err | | ----------------------- | --------- | ------------ | ------ | ---------------- | ---- | | 2025-04-04 15:42:35.500 | UCAS-70 | 6×180 | B | 18.73 | 0.24 | | 2025-04-04 15:45:44.199 | UCAS-70 | 6×180 | V | 17.89 | 0.12 | | 2025-04-04 15:48:52.780 | UCAS-70 | 6×180 | R | 17.18 | 0.14 | | 2025-04-04 15:52:01.952 | UCAS-70 | 6×180 | I | 16.76 | 0.13 | | 2025-04-04 16:04:43.721 | XL-C14 | 11×120 | g | <22.10( 3-sigma limit) | | | 2025-04-04 16:17:19.682 | XL-C14 | 13×120 | r | 17.59 | 0.19 | | 2025-04-04 16:15:12.716 | XL-C14 | 13×120 | i | 17.15 | 0.20 | | 2025-04-04 15:58:22.729 | XL-C14 | 8×120 | z | <17.41( 3-sigma limit) | | This measurement has not been corrected for galaxy extinction. Our observations are consistent with other already reported 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), Lipunov et al. (GCN 40066), Min-He et al. (GCN 40069), Lipunov et al. (GCN 40070), Perez-Fournon et al. (GCN 40071), Jelinek et al. (GCN 40072), Rakotondrainibe et al. (GCN 40073), Taguchi et al. (GCN 40074), Brivio et al. (GCN 40075), Ruocco (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), Chen et al. (GCN 40088), Chen et al. (GCN 40089), Pankov et al. (GCN 40090), Leonini et al. (GCN 40093), Leonini et al(GCN40095). View this GCN Circular online at https://gcn.nasa.gov/circulars/40097. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...