Extinction Curves from Gamma-ray Burst Afterglows Johan Fynbo Dark Cosmology Centre/Niels Bohr Institute/Copenhagen Work done by many: Andersen, Elíasdóttir, Gorosabel, Hjorth, Jakobsson, Jaunsen, Jensen, Ledoux, Leloudas, Levan, Malesani, Milvang-Jensen, Starling, Tanvir, Vreeswijk, Wiersema, Watson, Zafar, Xu, and several more

Gamma-ray bursts ARA&A reviews: van Paradijs, Kouveliotou & Wijers 2000, Mészáros 2002, Woosley & Bloom 2006

Theoretical afterglow spectra N(e) (Sari, Piran & Narayan 1998) N(e) e-p cooling e Low-frequency synchtron Self-absorbed fast cooling  ~ B e2

Extinction curves from GRB afterglows The approach is simple: The amount and properties of the dust is inferred from the deviations from a power-law spectrum. Reichart (1998), Jakobsson et al. (2003)

How we observe Mainly carried out at the ESO Very Large Telescope using one of the FORS1/2 instruments. Long-slit, low-resolution spectroscopy or broad band imaging. The instruments have “atmospheric dispersion correctors”. The spectra are flux-calibrated using observations of spectro-photometric standard stars.

GRB071031, z=2.69, no extinction

GRB050401, z=2.89, VLT, substantial SMC-like reddening 2175Å bump Watson et al. 2006

GRB050401, z=2.89, VLT, substantial SMC-like reddening Low dust-to-metals ratio, but significant depletion (?) 2175Å bump Watson et al. 2006

z=2.45, VLT, 2175Å bump 2175Å bump Eliasdóttir et al. 2009, Kruehler et al. 2008

GRB080605, z=1.65, VLT Xu et al. 2009

z=3.04, VLT, 2175Å bump Prochaska et al. 2009

z=1.50, strong reddening (in a blue host)

z=0.84, reddening?

Building a complete sample of Swift GRBs Gehrels et al. 2004, Schady et al. 2007, Evans et al. 2009 X-ray selected sample Jakobsson et al. 2006, A&A, 447, 897; Fynbo et al., in prep) March 2005 - September 2008: 146 bursts 106 optical afterglows detected 71 redshifts from afterglow spec.

QSO-DLAs and GRB absorbers

Evidence for many more dusty sightlines

Hauser & Dwek, ARA&A 2001

“Thermal emission from dust dominates the EBL spectrum at wavelengths longward of 3.5μ and constitutes about 48% of the nominal EBL. However, values ranging from 20% to 80% are consistent with the measurement uncertainties (shaded area).” GRBs could in principle provide a star-formation weighted mean extinction curve and its evolution with redshift. This would be a central element to establish for the interpretation of the EBL spectrum. Hauser & Dwek, ARA&A 2001

? Lyman-a galaxies SMGs Distant red galaxies GRB hosts Damped Lyman-a Absorbers Where are the bulk of the massive stars formed ? GRBs may give the answer Lyman-a galaxies Lyman-break galaxies SMGs