TITLE: GCN CIRCULAR NUMBER: 36999 SUBJECT: EP240801a: GMG observation DATE: 24/08/01 17:06:44 GMT FROM: Rui-Zhi Li at Yunnan Observatories, CAS liruizhi@ynao.ac.cn
R.-Z. Li, B.-T. Wang, J. Mao, X.-L. Zhang and J.-M. Bai (YNAO, CAS) report:
We observed the field of EP240801a (Zhou et al., GCN 36997, T0 at 2024-08-01T09:06:03) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2024-08-01T16:19:22, about 7.22 hours after the trigger.
The optical counterpart of EP240801a, not visible in the Pan-STARRS1 r-band image, was marginally detected at the coordinates (J2000): RA = 23h00m39.02s DEC = +32d35m37.2s , with a positional uncertainty of 0.5" or better. The position is consistent with TRT observation (GCN 36998).
The preliminary analysis results are shown as follows: +---------------+------------+----------+--------------+--------------+ | Tmid-T0 [h] | Exp. [s] | Filter | Mag | 5-sigma UL | +===============+============+==========+==============+==============+ | 7.39 | 1200 | R | 21.21 ± 0.12 | 21.9 | +---------------+------------+----------+--------------+--------------+ The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.092 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011).
We note that this optical counterpart has become fainter compared to the TRT observation (R = 20.32 ± 0.16 mag, GCN 36998).
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