GCN Circular 587
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 We report an improved near-infrared photometry of the proposed OT for GRB000301C in our J,H,K' images taken with IRCS (InfraRed Camera and Spectrograph) on the SUBARU Telescope on March 3.55 UT. Photometry was performed on co-added image (18-min total exposure time) while quick photometry of one K' frame (2-min exposure) was reported in GCNC #577. Seeing was approximately 0.45" in K' and 0.50" in J/H throughout the observation. The OT magnitudes were determined with about 0.01 mag statistical accuracy in all bands. Relative magnitudes of the OT to the near-by bright star (5.7" W and 1" S) were derived and compared to the results by Rhoads & Fruchter (GCN #586) to examine possible near-infrared decay of the OT. The results are as follows: relative magnitude(OT-Star) Reference J H K' UT 3.55 March 2.27 2.18 1.56 this work UT 4.64 March 2.47 ---- 1.69 GCNC #586 decay/day 0.20 ---- 0.13 Since we expect the uncertainty of relative photometry is quite small (e.g., 0.01 mag), these results suggest that the OT is actually fading in the near-infrared. The near-infrared decay rate is smaller compared to the R-band decay rate (~0.4-mag/day) of the same period. The slightly larger decay in J compared to K' may suggest that the decay rate is smaller in longer wavelengths. The possible host galaxy reported by Rhoads & Fruchter (GCN #586) is also detected in our images. It looks slightly extended (FWHM=0".6-0".7) in our K'-images of 0".45 seeing, which suggests that this source is actually a galaxy. This message is quotable in publications.