GCN Circular 20647

K. Wiersema, N. R. Tanvir (U. Leicester), A. J. Levan (U. Warwick),
R. Karjalainen, F. Riddick (ING) report on behalf of a larger collaboration:

We observed the field of Swift GRB 170208B (Siegel et al. GCN 20632
Not found
 
 
)
with the 4.2m William Herschel Telescope on La Palma.
Images were obtained in the Y,J,H,K filters with LIRIS.

In the K-band exposure, for which the mid-time was 2.54 hr post-burst,
we find a source with magnitude K(AB)=21.1+/-0.1 within the revised
X-ray error circle (Goad et al. GCN 20635
Not found
 
 
).

The source is absent (or very marginally present) in the other infrared
filters, which were observed somewhat earlier, to AB mag limits of
about 22.5 in each band.

The position of this source is:
RA(2000)=08:28:34.55
dec(2000)=-9:01:47.8

This is about 1.8 arcsec south of the steady optical source
seen by GROND and Pan-STARRS (Kruehler GCN 20640
Not found
 
 
; 
we note there was a typo in the declination coordinate 
reported in GCN 20640
Not found
 
 
, Kruehler priv. comm.).  

We suggest that the K-band source is most likely the 
afterglow of the GRB, and is not seen in bluer filters 
due to dust extinction, while the optical source may be the 
host galaxy.