GCN Circular 37453

SVOM/VT commissioning team: Y. L.Qiu, L. P. Xin, H. L. Li, C. Wu, X. H. Han, H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, L. Lan, W. J. Xie,  X. M. Lu, R. S. Zhang, D. W. Xu, G. W. Li (NAOC), J. Zhang, L. J.  Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM) and  J.Palmerio (CEA).

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), JeanLuc Attéia (IRAP), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Bing Zhang (UNLV) report on behalf of the SVOM team:

During the commissioning phase of SVOM mission, we observed the field of the GRB 240905E (Dichiara et al., GCN 37397
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; Zhang et al., GCN 37404
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)  with SVOM/VT telescope in ToO mode. The first observations started at 2024-09-06T15:04:16 UT, about 20.6 hours after the burst,and lasted for about 3 ks. The second observations started at 2024-09-08T12:25:52 UT, about 42.0 hours after the burst and lasted about 6 ks. VT made the observations with two channels simultaneously, VT_B (400nm-650nm) and VT_R (650nm-1000nm). 

We did not detect any new optical source in the errorbox of  Swift-XRT (Ferro et al., GCN 37406
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) in our stacked images down to the 3 sigma upper limit magnitude of about 23.5 mag in AB magnitude for both bands.

Our upper limit results are consistent with others (Lipunov et al., GCN 37398
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; An et al., GCN 37399
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; Moskvitin et al., GCN 37401
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; Swift/UVOT team, GCN 37402
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; Strausbaugh et al., GCN 37403
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; Brivio et al., GCN 37408
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; Fu et al., GCN 37409
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, GCN 37412
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; Adami et al., GCN 37413
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; WU et al., GCN 37414
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; Odeh et al., GCN 37419
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; Maksut et al., GCN 37420
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; Fu et al., GCN 37422
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 Mohan et al.). 

For the optical candidate near the errorbox of the location of X-ray afterglow (GCN 37415
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, Belkin et al.,).  It  was not detected in VT_B stacked images in both VT observations, but it was bright in VT_R stacked images in both observations, and its brightness had no apparent changes in brightness (VT_R=22.1+/-0.1 mag) in both observations. We also noted that near the position of the optical candidate (GCN 37415
Not found
 
 
, Belkin et al.,), there is a faint and red source in the Pan-STARRS catalog with a similar brightness measured in VT images.


More detailed analysis is ongoing.
 
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 is an optical telescope on board SVOM with an aperture of 44 cm, designed to automatically follow the Eclairs triggers. It has two channels: VT_B and VT_R, covering wavelengths from 400 nm to 650 nm and 650 nm to 1000 nm, respectively. The two bands are observed simultaneously. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.