TITLE: GCN CIRCULAR NUMBER: 18239 SUBJECT: ANTARES neutrino detection and Swift/XRT counterpart: GMG observation DATE: 15/09/04 19:02:05 GMT FROM: Jirong Mao at Yunnan Obs J. Mao, W. Yi, C. Wang, and J.-M. Bai (YNAO) report: We observed the star which is located at the position provided by Swift observation for the suggestion of X-ray counterpart of ANTARES neutrino detection (Dornic et al., GCN 18231, de Ugarte Postigo et al., GCN 18236) with the 2.4-meter GMG optical telescope of Yunnan Observatories. Observations began from 12:34:40 UT, Sep. 4, 2015. Under the poor observational condition, we obtained a spectrum covered effective wavelength range between 5500A and 9000A. We preliminarily checked the spectrum, and clearly identified some absorption lines (e.g., strong Na D line) and H alpha emission line. Further careful analysis is ongoing. We thank P. Evans for the information of X-ray observation. We also thank S. Basa, P. D'avanzo, J.-S. Huang, Y.-Z. Fan, D. Xu, and F. Yuan for their discussion.