GCN Circular 6032
Subject
GRB 070125: Keck/LRIS Spectroscopy -- Evidence for a very low redshift
Event
Date
2007-01-26T08:07:20Z (18 years ago)
From
Jason Prochaska at UCO/Lick Obs <xavier@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."