TITLE: GCN CIRCULAR NUMBER: 16333 SUBJECT: Swift Trigger 600114 in M31: Archival and Prompt UVOT Imaging DATE: 14/05/28 03:19:10 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team: Archival UVOT images of the transient reported in M31 (Barthelmy et al., GCN Circ. 16332) from July 2009 and November 2011 show the known globular cluster B045-G108 at the reported UVOT position, 4.5 arc-seconds from the position of the X-ray transient. Although a direct comparison is not possible at this time, we measure the following magnitudes for the object, before and after the trigger, using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373): Archival: Filter Mag uvw2 19.4+-0.1 uvm2 19.6+-0.2 uvw1 18.2+-0.1 Prompt: u 17.1+-0.2 white 16.9+-0.1 The post-explosion u magnitude would be roughly consistent with the pre-explosion NUV magnitudes given the SED of a typical M31 globular cluster. However, without processing of the full post-outburst data set, we cannot determine if the source has varied in the UV since 2011.