TITLE: GCN CIRCULAR NUMBER: 44284 SUBJECT: EP260321a: SVOM/VT optical observations and color changes around peak DATE: 26/04/13 10:24:49 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, Y. N. Ma, C. Wu, L. P. Xin, Y. L. Qiu, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed several ToO observations of EP260321a triggered by Einstein Probe (Huang et al., GCN 44068) in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously from 2026-03-21 (Ma et al., GCN 44074), 2026-03-23, 2026-03-26, 2026-03-28, 2026-04-01, 2026-04-04, 2026-04-07, 2026-04-10 and 2026-04-12. The optical counterpart (Lee et al., GCN 44070; Tanvir et al., GCN 44082; Moran et al., GCN 44083, Ahumada et al., GCN 44084, Liu et al., GCN 44087; Sankar et al. GCN 44089; de Ugarte Postigo et al., GCN 44091; Xu et al., GCN 44092; Pankov et al. GCN 44103; Corcoran et al., GCN 44105; Rastinejad et al., GCN 44107; Gao et al., GCN 44110; He et al., GCN 44117; Zhang et al., GCN 44171) showed a rise to a peak after trigger in both channels, followed by a decline. The peak in VT_B was at approximately 10.7 days post trigger. The preliminary measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 1.906 hr VT_B 53*50 sec 19.70+/-0.05 mag 1.906 hr VT_R 53*50 sec 19.98+/-0.06 mag 19.75 d VT_B 17*50 sec 17.48+/-0.03 mag 19.75 d VT_R 17*50 sec 17.21+/-0.02 mag One should be cautious that the brightness mentioned above may be contaminated by the host. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44284. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...