TITLE: GCN CIRCULAR NUMBER: 10672 SUBJECT: GRB 100424A: WHT z-band observations DATE: 10/04/25 02:12:06 GMT FROM: Andrew Levan at U.of Leicester A.J. Levan, C. Copperwheat, E. Breedt (U. Warwick), D. Malesani (DARK/NBI) report on behalf of a larger collaboration: "We observed the localization of GRB 100424A (Hoversten et al. GCN 10667) using the WHT and ACAM. Observations begin at April 25 00:18, approximately 9 hours after the burst. We obtained 4x200s exposures in the z-band. No source is visible within the enhanced XRT location (Evans et al. GCN 10669) to a limiting magnitude of z>23.2, calibrated against SDSS. The deep z-band limit, coupled with apparently bright early X-ray afterglow is suggestive of either a highly extinguished, or high redshift burst."