TITLE: GCN GRB OBSERVATION REPORT NUMBER: 577 SUBJECT: GRB000301C, near-infrared observations (JHK' photometry) DATE: 00/03/03 23:39:15 GMT FROM: Naoto Kobayashi at SUBARU, NAOJ Naoto Kobayashi (Subaru Telescope, National Astronomical Observatory of Japan), Miwa Goto, Hiroshi Terada (Kyoto University), Alan T. Tokunaga (Institute for Astronomy, University of Hawaii), on behalf of SUBARU Telescope team and SUBARU IRCS team On 3 March, 12:48 UT - 13:54 UT, we observed the candidate optical counterpart to GRB 000301C that was reported by Fynbo et al. (GCN Circular #570). We used the Subaru 8m Telescope on Mauna kea with a new instrument IRCS (Infrared Camera and Spectrograph for the Subaru Telescope) during its first engineering run. Near-infrared J,H,K' filters were used. The candidate optical transient (OT) was clearly detected in all three bands. We have performed preliminary photometry with 2-arcsecond aperture using Persson standards taken during the night. The resultant magnitude of the candidate OT was K'=17.6+-0.1 mag. For reference, the magnitude of the near-by star, USNO 125_07686794, was estimated at K'=16.0+-0.05 mag. Comparing to the estimated K' magnitude of 17.4 (at 4:41 UT - 5:38 UT) reported by Stecklum et al (GCN Circular #572), our photometry may suggest that the brightness decreased by roughly 0.2 mag during 8 hours. However, given the possible systematic errors for the two estimates (e.g., photometric system is different), further observations are necessary to confirm this OT candidate as the GRB afterglow. This message is quotable in publications.