TITLE: GCN CIRCULAR NUMBER: 24249 SUBJECT: LIGO/Virgo S190426c: Tentative Red Transient Candidate from Las Cumbres Observatory DATE: 19/04/26 21:16:24 GMT FROM: Iair Arcavi at LCOGT Iair Arcavi (Tel Aviv University), Curtis McCully (LCO), Daichi Hiramatsu (LCO/UCSB), D. Andrew Howell (LCO/UCSB), Jamison Burke (LCO/UCSB), Craig Pellegrino (LCO/UCSB) on behalf of the Las Cumbres GW Follow-up Collaboration We detect a possible transient at RA Dec 217.28296 -38.190458, which we tentatively name “Nemo”, on the outskirts of the galaxy 2MASX J14290828-3811214 (redshift 0.07478 / distance 338 Mpc; Jones et al. 2009, “The 6dF Galaxy Survey Data Release 3,” via NED). We measure a preliminary aperture magnitude of 19.74 +- 0.12 in the i-band (but host contamination is likely) in a 300s image taken on 2019-04-26 18:19:33 UT at a Las Cumbres SAAO 1m telescope. This corresponds to an absolute magnitude of -17.9 at this distance. These values are corrected for MW extinction (E(B-V) = 0.0874; Schlafly, E.F. & Finkbeiner, D.P. 2011, ApJ 737, 103). “Nemo” is not visible in g-band images taken at the same time (2019-04-26 18:13:52 UT) using a Las Cumbres SAAO 1m. The source does not appear in DSS red or blue images, though they are not as deep as our discovery image. The transient is also not visible in images taken from the Las Cumbres Observatory 2m Faulkes telescope in the i band at 16:27:54, the r band at 16:33:39 , and the g band at 16:39:24 (all on 2019-04-26; all times UT) but these images are also shallower than the discovery image. Therefore the transient nature of “Nemo” is not yet confirmed.