TITLE: GCN CIRCULAR NUMBER: 25720 SUBJECT: LIGO/Virgo S190910d: Liverpool Telescope spectroscopy of ZTF19abyfazm DATE: 19/09/10 21:48:22 GMT FROM: Daniel Perley at Liverpool JMU D. A. Perley and C. M. Copperwheat (LJMU) report on behalf of the GROWTH collaboration: We acquired imaging and spectroscopy of ZTF19abyfazm/AT2019pwa (Anand et al., GCN 25706), an optical transient within the error region of gravitational wave trigger S190910d (LVC et al. GCN 25695), with the 2m Liverpool Telescope. A sequence of 60-second images was acquired in g, r, and i filters using IO:O, followed by 2x500s of spectroscopy with SPRAT, between 20:53 and 21:20 on 2019-09-10 (UT). The source remains bright and blue, although has faded slightly since the time of ZTF discovery (we measure AB magnitudes of g=17.95, r=18.30, i=18.65 at approximately MJD=58736.87). No significant absorption or emission features are visible in the spectrum. We conclude that this source is likely the eruption of an uncatalogued cataclysmic variable within our Galaxy, although further monitoring will be needed to confirm this. We thank the MOPTOP commissioning team for their patience while acquiring these observations. DisclaimerNone