TITLE: GCN CIRCULAR NUMBER: 38516 SUBJECT: GRB 241209B: SVOM/VT afterglow detection DATE: 24/12/10 07:47:55 GMT FROM: Chao Wu at NAOC cwu@nao.cas.cn
SVOM/VT commissioning team: Y. L. Qiu, H. L. Li, L. P. Xin, C. Wu, X. H. Han, J. Wang, W. J. Xie, H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, J. S. Deng, L. Lan, X. M. Lu, R. S. Zhang, D. H. Zhao (NAOC), J. Zhang, L. J. Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM), H. Zhou (PMO), C. Plasse (CEA)
SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), 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), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV)
report on behalf of the SVOM team:
The GRB 241209B (Xie et al., GCN 38478) was observed by on-board VT after the automatic slew of the platform. The VT conducted observations in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. Revisit observation (TOO-EX mode) was also operated ~ 10 hr after the trigger.
An uncatalogued optical source was detected in VT_B and VT_R band images within the errorbox of source #1 reported by Swift team (GCN 38494), which is 5.7 arcmin to the center of ECLAIRs localization, and further confirmed with the data from revisit observation. The source is located at RA, Dec = 194.63406, +76.17617 which is equivalent to:
RA (J2000) : 12h 58m 32.17s Dec (J2000): +76d 10' 34.2"
with an uncertainty of 0.5 arcsec.
Its brightness was fading for ~1 magnitude in both of VT_B and VT_R images in the initial 10 hours. The magnitude was VT_B= 23.20 +/-0.20 mag and VT_R= 21.75 +/-0.05 mag in AB magnitude at 2024-12-09T05:04:49 UT, about 1.14 hr post the trigger.
We proposed that this source is the optical counterpart of the burst.
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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