TITLE: GCN CIRCULAR NUMBER: 38636 SUBJECT: EP241217a: 1.6m Mephisto multi-band optical observations DATE: 24/12/19 15:07:39 GMT FROM: Brajesh Kumar at SWIFAR, YNU brajesh@ynu.edu.cn
Dezi Liu, Yu Pan, Xiangkun Liu, Brajesh Kumar, Xianao Wang, Chenxi Shang, Xufeng Zhu, Yuanpei Yang, Xingzhu Zou, Xinlei Chen, Yehao Cheng (all SWIFAR, YNU), Ye Li (PMO, CAS), Guowang Du, Tao Wang, Yuan Fang, Jinghua Zhang, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
We observed the field of EP241217a reported by EP-WXT (Zhou et al., GCN 38586) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous multi-band uvgriz band observations were initiated on 2024/12/17 between 14:07:34 to 15:48:12 UT. Multiple frames were obtained with exposure times of 180s and 300s in different bands. In our r i z band images, there is clear detection of the optical counterpart candidate (Levan et al., GCN 38587; Izzo et al., GCN 38588; Fan et al., GCN 38592; Jin et al., GCN 38607; Mohan et al., GCN 38612; Zhu et al., GCN 38613; Bochenek et al., GCN 38615) but no detection in the stacked images of u v g bands. The field was observed again in uvgriz bands on 2024/12/18 (starting from 12:43:30 UT) and three frames of 300s in each band were taken. We found a marginal detection of the transient in the i band stacked image but not in other bands. Our preliminary results for the initial frames for 2024/12/17 and 2024/12/18 (upper limits indicate 3 sigma) are listed below:
UT start band Exp Mag/LimMag(AB) 2024/12/17T14:07:34 z 180s 18.73 +/- 0.13 2024/12/17T14:11:28 r 300s 21.15 +/- 0.27 2024/12/17T15:05:43 i 300s 19.34 +/- 0.06 2024/12/17T15:24:11 g 300s*6 >23.15 2024/12/17T15:24:11 u 300s*6 >22.64 2024/12/17T14:50:44 v 300s*7, 180s*1 >22.88
2024/12/18T13:00:36 u 300s*3 >22.91 2024/12/18T13:00:36 g 300s*3 >22.91 2024/12/18T12:43:30 v 300s*3 >22.80 2024/12/18T12:43:30 r 300s*3 >22.65 2024/12/18T12:43:30 z 300s*3 >20.62 2024/12/18T13:00:36 i 300s*3 21.99 +/- 0.52 ------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. --------------------------------------------------------------------------
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