TITLE: GCN CIRCULAR NUMBER: 20757 SUBJECT: LIGO/Virgo G275404: Keck spectrum of MASTER OT J105958.00-115756.5 DATE: 17/02/26 19:08:17 GMT FROM: Igor Andreoni at Swinburne U of Tech J. Cooke, I. Andreoni, U. Mestric (Swinburne Univ.), T. Moriya (NAOJ) A spectrum of the MASTER transient OT J105958.00-115756.5 (GCN Circ. 20748) was taken with the Keck telescope on 2017-02-26.54 UT during the follow up of the LIGO event G275404 (LIGO/VIRGO Collaboration GCN Circ. 20738). The observations were performed with the Low Resolution Imaging Spectrometer for a total exposure time of 2300s under several magnitudes of variable cloud extinction. The preliminary analysis reveals a blue and mostly featureless spectrum at redshift z=0.0017. The spectrum shows evidence of Balmer series lines in absorption, with a potential weak emission in the H-gamma trough. This result is not inconsistent with Lipunov et al. (GCN Circ. 20748), who suggest the event to be a CV.