TITLE: GCN CIRCULAR NUMBER: 10671 SUBJECT: GRB 100424A: NOT optical observations DATE: 10/04/25 01:19:23 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Malesani (DARK/NBI), D. Xu (Weizmann Inst.), A. J. Levan (Univ. Warwick), P. Jakobsson (Univ. Iceland), T. Pursimo (NOT), report on behalf of a larger collaboration: We observed the field of GRB 100424A (Hoversten et al., GCN 10667) with the NOT equipped with ALFOSC in the R, I, and z filters. Observations started on April 24 at 22:38, 23:05, and 23:31 UT in R, I, z, respectively (6.30, 6.74, and 7.21 hr after the GRB), and were affected by the closeby bright Moon (42 deg away, 85% full) and some clouds. We do not detect any new object within the refined XRT error circle (Evans, GCN 10668; Evans et al., GCN 10669). The limiting magnitudes are R(Vega) = 22.5 and z(AB) = 21.9, calibrated against the USNO-B1 and SDSS catalogs, respectively. Given the relatively large X-ray flux, we encourage NIR observations.