[AAVSO-HEN] GRB 070521: Subaru observations and possible host detection

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
For an archive and more information on circulars visit:
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TITLE:   GCN CIRCULAR
NUMBER:  6444
SUBJECT: GRB 070521: Subaru observations and possible host detection
DATE:    07/05/21 23:46:59 GMT
FROM:    Nobuyuki Kawai at Tokyo Tech  <nkawai at hp.phys.titech.ac.jp>

T. Hattori, K. Aoki (Subaru Telescope, NAOJ), and N. Kawai
(Tokyo Tech) report on behalf of the Subaru GRB team:

"We observed the field of GRB 070521 (Guidorzi et al., GCN 6431) 
with FOCAS on the Subaru Telescope starting at 07:31(UT) (40 min after
the trigger) with total exposures of 1920 sec (120s x 16) in z'-band 
and 360 sec (120s x 3) in i'-band.  

We detected a faint source inside the XRT error circle at

RA=16:10:38.55, DEC=30:15:27.7 

with a positional uncertainty of 0.5"
and an approximate magnitude of z' ~ 23.5.

We obtained 3600 sec long-slit spectra of this faint source 
covering a wavelength range from 6000 to 10000 Ang.  
We detected [O III] 5007, 4959 emission lines at z=0.553.
If this object is the host galaxy of GRB 070521, its location at a
relatively low redshift makes it a good candidate for searching the
supernova component.  Note, however, that the absence of a bright
afterglow may indicate that the GRB source is embedded in a region
with high extinction, or the host identification is spurious. 

The image may be viewed at 
http://www.hp.phys.titech.ac.jp/nkawai/grb/070521/.

We thank the Subaru Observatory for the support of this observation."