Watson, D.; Fynbo, J. P. U.; Ledoux, C.; Vreeswijk, P.; Hjorth, J.; Smette, A.; Andersen, A. C.; Aoki, K.; Augusteijn, T.; Beardmore, A. P.; Bersier, D.; Castro Cerón, J. M.; D'Avanzo, P.; Diaz-Fraile, D.; Gorosabel, J.; Hirst, P.; Jakobsson, P.; Jensen, B. L.; Kawai, N.; Kosugi, G.; Laursen, P.; Levan, A.; Masegosa, J.; Näränen, J.; Page, K. L.; Pedersen, K.; Pozanenko, A.; Reeves, J. N.; Rumyantsev, V.; Shahbaz, T.; Sharapov, D.; Sollerman, J.; Starling, R. L. C.; Tanvir, N.; Torstensson, K.; Wiersema, K.
Bibliographical reference
The Astrophysical Journal, Volume 652, Issue 2, pp. 1011-1019.
Advertised on:
12
2006
Journal
Citations
134
Refereed citations
124
Description
The optical afterglow spectrum of GRB 050401 (at z=2.8992+/-0.0004)
shows the presence of a damped Lyα absorber (DLA), with
logNHI=22.6+/-0.3. This is the highest column density ever
observed in a DLA and is about 5 times larger than the strongest DLA
detected so far in any QSO spectrum. From the optical spectrum, we also
find a very large Zn column density, implying an abundance of
[Zn/H]=-1.0+/-0.4. These large columns are supported by the early X-ray
spectrum from Swift XRT, which shows a column density (in excess of
Galactic) of logNH=22.21+0.06-0.08
assuming solar abundances (at z=2.9). The comparison of this X-ray
column density, which is dominated by absorption due to α-chain
elements, and the H I column density derived from the Lyα
absorption line allows us to derive a metallicity for the absorbing
matter of [α/H]=-0.4+/-0.3. The optical spectrum is reddened and
can be well reproduced with a power law with SMC extinction, where
AV=0.62+/-0.06. But the total optical extinction can also be
constrained independent of the shape of the extinction curve: from the
optical to X-ray spectral energy distribution, we find
0.5<~AV<~4.5. However, even this upper limit,
independent of the shape of the extinction curve, is still well below
the dust column that is inferred from the X-ray column density, i.e.,
AV=9.1+1.4-1.5. This discrepancy might
be explained by a small dust content with high metallicity (low
dust-to-metals ratio). ``Gray'' extinction cannot explain the
discrepancy, since we are comparing the metallicity to a measurement of
the total extinction (without reference to the reddening). Little dust
with high metallicity may be produced by sublimation of dust grains or
may naturally exist in systems younger than a few hundred megayears.
Based in part on observations made at the European Southern Observatory,
Paranal, Chile under program 075.D-0270, with the Nordic Optical
Telescope, operated on the island of La Palma jointly by Denmark,
Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del
Roque de los Muchachos of the Instituto de Astrofisica de Canarias, with
the Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope,
which is operated by the Joint Astronomy Centre on behalf of the UK
Particle Physics and Astronomy Research Council, and on data collected
at the Subaru Telescope, which is operated by the National Astronomical
Observatory of Japan.