1. 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

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

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

4. 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)

5. 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.

6. GRB071031, z=2.69, no extinction

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

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

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

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

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

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

13. z=0.84, reddening?

14. 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 September 2008:
146 bursts
106 optical afterglows detected
71 redshifts from afterglow spec.

15. QSO-DLAs and GRB absorbers

16. Evidence for many more dusty sightlines

17. Hauser & Dwek, ARA&A 2001

18. “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

19. ? 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