[vsnet-grb-info 5874] GRB 080325: Subaru detection of NIR afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7524
SUBJECT: GRB 080325: Subaru detection of NIR afterglow candidate
DATE:    08/03/27 06:50:55 GMT
FROM:    Nobuyuki Kawai at Tokyo Tech  <nkawai at hp.phys.titech.ac.jp>

I. Tanaka, T.-S. Pyo, T. Hattori, K. Aoki (Subaru, NAOJ), C. Tokoku,
T. Yamada (Tohoku U), K. Ohta (Kyoto U), and N. Kawai (Tokyo Tech)
report on behalf of the Subaru GRB team:

We observed the field of GRB 080325 (Vetere et al., GCN 7512) with
MOIRCS on the Subaru Telescope in J and Ks bands starting at 12:51 UT,
March 25, about 8.7 hours after the trigger.  The observation lasted
until 15:43 UT with effective exposures of 18 min in J band and 80 min
in Ks band.  We detected a faint extended object (Ks=19.5) in the
enhanced Swift XRT error circle (Osborne et al., GCN 7513).  We
measure the coordinates of its center as:

18:31:34.24 +36:31:24.3 (J2000, uncertainty 0".3).

There seemed to be a bright spot at the north end of this object.

We performed another set of observation with MOIRCS at March
26.5-26.7 in Ks and J bands.  We confirmed that the north spot of the
source had faded significantly, and the total magnitude of the source
had faded by 0.5 mag.

Based on the positional coincidence and the fading behavior, we
suggest that the faint extended source is the host galaxy of GRB
080325, and the spot in the north was the afterglow.

The source 6" south of the enhanced Swift-XRT error circle reported by
Updike et al. (GCN 7515) was also present in our image, and we measure
its magnitude at ~14:00 UT, March 25 (10 hours after the trigger) as:

J = 18.62 +/- 0.03,

consistent with the magnitude reported by Clemens et al. (GCN 7520).  
Thus it is not likely to be the afterglow of the GRB.