GCN Circular 35002

Tian-Rui Sun, Xin-Lei Chen, Xiangkun Liu, Yuan-Pei Yang, Tianyu Zhang, Helong Guo, Guowang Du, Haipeng Lei, Brajesh Kumar, Xiaowei Liu report on behalf of the Mephisto Collaboration:

Following the detection of GRB 231111A by SWIFT (Melandri et al., GCN 34981
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, Osborne et al., GCN 34991
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 and GCN 34995
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), MASTER (Lipunov et al., GCN 34980
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, GCN 34983
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) , Nanshan/HMT (Jiang et al., GCN 34982
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), Git (Kumar et al., GCN 34984
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), YAHPT (Sun et al., GCN 34985
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), Gecam (Zhang et al, GCN 34990
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 and 34993
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), Mondy (Pankov et al., GCN 34994
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), Terskol Zeiss-2000 (Pankov et al., GCN 34996
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), Nastro Verde (Dainotti et al., GCN 34997
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), GMG (Mao et al., GCN 34999
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, GCN 35001
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), we conducted observations using the Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University at Lijiang Observatory (IAU code: 044) of Yunnan Astronomical Observatories, Chinese Academy of Sciences (CAS) to search and follow up its afterglow near SWIFT/UVOT position.

We simultaneously observed the target position with 60s exposure in u/g bands and v/r bands starting from 11 Nov 2023, UTC 14:49:05, about 1905 seconds after the burst.

At the beginning of our observation:
Filter     |Mag  |Magerr | Time                  |reference 
Mu         |19.48| 0.12  | 2023-11-11T14:56:35   |Mephisto u
Mv         |19.13| 0.07  | 2023-11-11T14:49:05   |Mephisto v
Mg         |18.65| 0.04  | 2023-11-11T14:56:35   |Mephisto g
Mr         |18.15| 0.04  | 2023-11-11T14:49:05   |Mephisto r

To do the flux calibration, we chose the exposure with the best image quality as the reference image, and used stars of signal-to-noise ratio (SNR) >30 after removing variables by cross-matching with variable catalogs in each band to scale the flux level to that of the reference image. Atmospheric extinction corrections and instrumental magnitude zero points are applied to the reference image.

Mephisto 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 will yield real-time, high-quality colors of unprecedented accuracy of billions of objects, enable fast and robust classification of variables and transients, and for the first time, deliver a panoramic and panchromatic documentary of our dynamic universe. The on-site telescope assemblage and commissioning were carried out in September 2022, and the first light with the small system of 4 filters (uviz) in dual channels was achieved on October 23, 2022. Mephisto is currently equipped with two commercial Andor iKon-XXL single-chip CCD cameras for the blue and yellow channels. Each camera covers an area about a quarter of the full field-of-view (2°in diameter).

[Editor's Note: The subject was modified at the user's request to list the correct GRB name.]