TITLE: GCN CIRCULAR NUMBER: 10690 SUBJECT: GRB 100424A: Gemini/NIRI H-band observations DATE: 10/04/26 07:27:45 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko, A. N. Morgan, and J. S. Bloom (UC Berkeley) report on behalf of a larger collaboration: We have obtained further imaging of the field of GRB 100424A (Hoversten et al., GCN 10667) with the Near InfraRed Imager and Spectrometer mounted on the 8 m Gemini North telescope. Following our report of a detection of a candidate afterglow in the J and K filters (Cenko et al., GCN 10682), we obtained a sequence of H-band images beginning at 9:29 UT on 25 April 2010 (~ 17 hours after the burst). The candidate afterglow is also detected in the H-band. Using the PAIRITEL imaging of the field for photometric calibration (Morgan and Bloom, GCN 10675), we measure a magnitude of H = 20.9 (Vega) at this time. Combined with our previous J and K photometry (and assuming the afterglow decays in time like a power-law with index alpha=-1), the candidate infrared afterglow appears consistent with a relatively steep spectral power-law index of beta ~ 2.5-3.0 across all three bands. This suggests the afterglow is reddened due predominantly to dust in the host galaxy of the GRB, and not an extremely high-redshift (z > 7) origin, as would be suggested by the presence of host galaxy extinction from the X-ray afterglow spectrum (Stroh et al., GCN 10674). We wish to thank the staff at Gemini Observatory for assistance in executing these observations.