[vsnet-grb-info 3165] GRB060418: Further Analysis of MIKE Spectroscopy

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5002
SUBJECT: GRB060418: Further Analysis of MIKE Spectroscopy
DATE:    06/04/24 17:27:34 GMT
FROM:    Jason Prochaska at UCO/Lick Obs  <xavier at ucolick.org>

J. X. Prochaska (UCO/Lick Observatory), H.-W. Chen (U Chicago), J. S.  
Bloom (UC
Berkeley), E. Falco, and A. K. Dupree (Harvard-Smithsonian CfA)  
report on behalf of the
GRAASP collaboration:

"We have further analyzed the echelle spectra of GRB060418 (Falcone  
et al.
GCN 4966), obtained using MIKE on the Magellan Clay telescope (Dupree  
et al.
GCN 4969).  We report the detection of ZnII, SiII, SiII*, FeII, FeII*,
MgII, MgI, AlIII, CIV and NiII transitions among others at a redshift
z=1.4901 +/- 0.0001.  The relative populations of the excited
FeII levels are similar to GRB051111 (PHB06, astro-ph/0601057); the  
J=7/2 to
J=1/2 states follow a Boltzmann distribution with T=1000-5000K.
But, following GRB051111 and GRB050730, we interpret the FeII excitation
as the result of indirect UV pumping by the GRB afterglow.  The  
detection
of strong MgI absorption places this gas (and presumably the majority of
low-ion gas) at a distance r>50pc from the GRB.  Finally, we measure
[Si/Fe]=+0.5dex indicating a modest dust-to-metals ratio.

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