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
Not found
 
 
) 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
Not found
 
 
) 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.

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