[vsnet-grb-info 4234] GRB 070125: Keck/LRIS Spectroscopy -- Evidence for a very low redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6032
SUBJECT: GRB 070125: Keck/LRIS Spectroscopy -- Evidence for a very low redshift
DATE:    07/01/26 08:07:20 GMT
FROM:    Jason Prochaska at UCO/Lick Obs  <xavier at ucolick.org>

Jason X. Prochaska (UCSC), Gijs Roelofs (Nijmegen), Joshua Bloom (UCB)
and Danny Steeghs (CfA) report on behalf of GRAASP:

"We observed the afterglow of GRB 070125 with the LRIS
dual spectrometer for 600s total starting at UT 05:44
under variable conditions.  Our high signal-to-noise
spectrum covers 3000-8000A and reveals no obvious absorption
or emission lines.   We place these constraints -- which are tighter
than those presented in GCN 6031 -- on the redshift:

(1) The absence of a Lyman limit requires z<2.3.
(2) The absence of a damped Lya profile or obvious Lya forest
requires z<1.4
(3) The absence of MgII absorption suggests z<0.1.

Given that strong MgII absorption is a signature of nearly
every long duration GRB to date, we have confidence in the third
conclusion.  On the other hand, the absence of obvious [OII] or Halpha
emission is surprising.   If the GRB is at very low redshift, the  
absence of
any source in the DSS imaging at this GRB position suggests a
significantly sub-L* host.

We strongly urge groundbased and spacebased follow-up programs
to plan an intensive campaign to search for and characterize any
associated supernova.

Further analysis is in progress."