GCN Circular 37526
Subject
GRB 240916A: JinShan optical decay in one of the two GOTO candidates
Date
2024-09-16T15:14:38Z (a month ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Q. Jiang, J. An, X. Liu, Z.P. Zhu, S.Y. Fu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the two GOTO optical counterpart candidates (Gompertz et al., GCN 37522) of GRB 240916A detected by Fermi/GBM (Fermi GBM Team, GCN 37518) and INTEGRAL SPI ACS (Pawar et al., GCN 37519), using the 100cm-C (100C) telescope of the JinShan project, located in Altay, Xinjiang, China. Observations started at 2024-09-16T13:38:03.01 UT, i.e., 12.25 hr after the Fermi/GBM trigger, and a series of Sloan r-band frames were obtained.
GOTO24fzk, also as AT 2024vlo, has r = 19.11 +/- 0.05 (AB) in our stacked image, via image subtraction and calibrated with Legacy Survey DR10. There is no apparent fading for this source, compared with L = 19.15 +/- 0.19 at the GOTO observational time. We thus think it's likely unrelated to the GRB.
GOTO24fzn, also as AT 2024vlp, has r = 18.69 +/- 0.05 (AB) in our stacked image, calibrated with Legacy Survey DR10. It has considerably faded, compared with L = 17.80 +/- 0.05 at the GOTO observational time. The decay rate is consistent with that for GRB optical afterglows.
We thus think GOTO24fzn/AT 2024vlp is likely the optical counterpart of GRB 240916A.
We acknowledge the excellent support from X. Yao, S.W. Luo, and Z.K. Feng for enabling these observations.