TITLE: GCN CIRCULAR NUMBER: 41122 SUBJECT: EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit DATE: 25/07/19 15:21:36 GMT FROM: Huali Li at at NAOC, SVOM lhl@nao.cas.cn
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM mission team.
SVOM/VT conducted two ToO follow-up observations of EP250702a (Cheng et al., GCNs 40906, 40917), which was likely associated with the long burst GRB250702B,D,E (Fermi GBM Team, GCNs 40883, 40886, 40890; DeLaunay et al., GCN 40903; Frederiks et al., GCN 40914; Wang et al., GCN 40923).
The first observation was made on July 3, 2025 in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously, between 10:54:08 and 15:10:00 (UTC), 32.0 to 36.3 hours after the EP/WXT trigger (Cheng et al., GCN 40906). The second one was made on July 5, 2025, between 08:56:18 and 15:41:13, 3.25 days to 3.53 days after the EP/WXT trigger (Cheng et al., GCN 40906).
The counterpart detected by VLT (Martin-Carrillo et al., GCN 40924; Levan et al., GCN 40961), MOSFIRE (Sharma et al., GCN 41044), HST (Levan et al., GCN 41096), MeerKAT (Bright et al., GCN 40985), VLA (Sfaradi et al., GCN 41053) and ALMA (Alexander et al., GCN 41059) was not detected in our images for both observations.
The 3 sigma upper limit magnitudes were estimated: Mid-time | Exposure time | Band | upper limit (AB) 34.2 hours | 80*100 sec | VT_R | 23.6 34.2 hours | 81*100 sec | VT_B | 23.8 3.53 days | 81*100 sec | VT_R | 23.6 3.53 days | 81*100 sec | VT_B | 23.8
The Mid-time above is the relative time from the trigger time of EP/WXT (Cheng et al., GCN 40906).
The result is consistent with the optical upper limit from GOTO (Kumar et al., GCN 40908), MASTER (Lipunov et al., GCN 40912), Colibri (Becerra et al., GCN 40918), CAHA (Pérez-García et al., GCN 40929), WFST (Hua et al., GCN 40943), FTW (Busmann et al., GCN 40949), UVOT (Siegel et al., GCN 40952), SYSU (Li et al., GCN 40986) and GRANDMA(Akl et al., GCN 41016).
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.
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