[vsnet-grb-info 10159] GRB 110128A: WHT redshifts of nearby field galaxies

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11608
SUBJECT: GRB 110128A: WHT redshifts of nearby field galaxies
DATE:    11/01/28 14:21:48 GMT
FROM:    Nial Tanvir at U.Leicester  <nrt3 at star.le.ac.uk>

N. R. Tanvir, K. Wiersema (U. Leicester), A. J. Levan (U. Warwick),
A. Kamble (U. Wisconsin), A. Cardwell (ING) and E. M. Ratti (SRON)
report on behalf of a larger collaboration:

We obtained spectroscopy of the afterglow of GRB 110128A (GCN 11603,
GCN 11605) and of two field galaxies nearby, using the 4.2 William Herschel
Telescope on La Palma.  Observations began at 04:26 UT, approximately 2.7 hours
post-burst, and comprised a 60 minute total exposure. The spectra cover a
wavelength range from about 4500A to 9400A.

The signal-to-noise, of the afterglow spectrum is not sufficient to confirm the
redshift reported in Sparre et al. in GCN 11607 (and note, our spectral range
did not cover the DLA feature), however we did measure the redshifts of
two field galaxies which are sufficiently close to the line of sight that they
might produce absorption in the afterglow:

Gal 1: RA=12:55:35.38, dec=+28:03:57.6
z=0.639 based on [OII]3727, CaII H & K, Hbeta
Offset from afterglow=5 arcsec, corresponding to ~35 kpc impact parameter to GRB

Gal 2: RA=12:55:36.40, dec=+28:04:12.1
z=0.109 based on Ha and [NII]
Offset from afterglow=25 arcsec, corresponding to ~50 kpc impact parameter to GRB