TITLE: GCN CIRCULAR NUMBER: 21459 SUBJECT: LIGO/Virgo G296853: BOOTES-1 and GTC optical observations DATE: 17/08/11 17:02:15 GMT FROM: Alberto J. Castro-Tirado at IAA-CSIC A. J. Castro-Tirado (IAA-CSIC and ISA-UMA), C. Pérez del Pulgar and R. Martín Márquez (ISA-UMA), A. Castellón (UMA), M. Jelínek (ASU-CAS), R. Cunniffe, Y. Hu and A. González-Rodríguez (IAA-CSIC), P. Peseev, G. Gómez and A. Alonso (GRANTECAN), on behalf of a larger collaboration report: In response to the LIGO/Virgo GW Binary Merger Candidate G296853 on Aug 9, 08:28 UT (GCNC 21431), a mosaic of unfiltered images covering 80% of the GraceDB skymap (above -45 in Dec) was taken starting on Aug 10, 01:30 UT (i.e. 17 hr later) with the wide-field imager at the BOOTES-1 station located at the ESAt/INTA-CEDEA in Mazagón (Huelva, Spain), down to a R = 12 limiting magnitude. In addition to this, data for several selected fields within the skymap center were gathered the same night with the 10.4m GTC telescope (+OSIRIS spectrograph) in riz filters down to R = 21.5, with the images quality being affected by the nearby full moon and the poor transparency due to the dust from Sahara. A more detailed analysis of the data is in progress.