The reanalysis of spectra of GRB 080913 to estimate the neutral fraction of the IGM at a redshift of 6.7

Aims. We reanalyse optical spectra of the z=6.7 gamma-ray burst GRB 080913, adding hitherto unpublished spectra, to reassess the measurement of the neutral fraction of the IGM at high redshifts. Methods. In the data reduction, we take particular care to minimise systematic errors in the sky subtract...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2010-03, Vol.512, p.L3
Main Authors: Patel, M., Warren, S. J., Mortlock, D. J., Fynbo, J. P. U.
Format: Article
Language:English
Subjects:
Astronomy
Breaking
Constraining
dark ages
Data reduction
Density
Earth, ocean, space
Exact sciences and technology
first stars
Fittings
gamma-ray burst: individual: GRB 080913
Mathematical models
Rations
reionization
Spectra
techniques: spectroscopic
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Summary:Aims. We reanalyse optical spectra of the z=6.7 gamma-ray burst GRB 080913, adding hitherto unpublished spectra, to reassess the measurement of the neutral fraction of the IGM at high redshifts. Methods. In the data reduction, we take particular care to minimise systematic errors in the sky subtraction, which are evident in the published spectrum, and compromise our analysis. The final combined spectrum has a higher signal-to-noise ration (S/N) than the previously published spectrum by a factor of 1.3. Results. We find a single significant absorption line redward of the Lyα continuum break, which we identify with the ii + Siii λ 0.126 μm blend, at z=6.733. The sharp spectral break at Lyα implies a comparatively low total column density of neutral hydrogen along the line of sight, $\log({N_\mathrm{HI}}$/cm-2)
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/200913876