1. Gamma-ray Burst Afterglow Spectroscopy J. P. U. Fynbo, Niels Bohr Institute / Dark Cosmology Centre

2. What is a gamma-ray burst? Brief (ms - min) and intense (~10 -7 erg cm –2 s –1 ) burst of soft (~100 keV) gamma-ray radiation  Discovered by chance in the 60ies  Rapid variability  Non-thermal spectra  About 1 per day with current sensitivities  The key problem in revealing their nature was getting precise positions.

3. GRB Afterglows Wijers et al. (1999); Covino et al. (1999); Beuerman et al. (1999); Vreeswijk et al. (2001) VLT/FORS1: Spectroscopic redshift: z = 1.62 Host: R(AB)>26 Detection of polarization

4. Halo HI, HII, H 2, metals, dust DM, supermassive BH GRB sightline protodisk HII regions QSO sightline Pontzen et al. (2008) (Cold) accretion IGM Outflows driven by SNe or AGN

5. The GRB/SN connection Strongest cases –980425/1998bw (z=0.0085) –030329/2003dh (z=0.1685) –031203/2003lw (z=0.1055) –060218/2006aj (z=0.033) –081007/2008hw (z=0.5295) –101219B/2010ma (z=0.55) –120422A/2012bz (z=0.283) –120714B/2012eb (z=0.398) E-ELT/HIRES would allow the study of this connection to higher redshifts (z>1). A resolution of R>3000 is needed to observe between the OH- lines. Woosley & Bloom 2006, ARA&A Hjorth et al. (2003)

6. GRB afterglow spectroscopy provides a unique probe of star- forming galaxies HI H 2 Metallicities Extinction curves UV-photon escape fraction Unique selection of star-forming galaxies (#massive stars per LF bin)

7. GRB030323 VLT + HST/ACS z = 3.371 Host: V(AB)=28.0 SFR = 1 M  /yr A V <0.5 mag [Fe/H]=-1.5 [S/H]=-1.3 Vreeswijk et al. (2004)

8. Building a representative sample Sample definition Jakobsson et al. 2006, A&A; Fynbo et al. 2009, ApJS) 1.T 90 > 2 sec 2.XRT localized within 12 hr. 3.Galactic A V < 0.5. 4.-70 o < declination < +70 o 5.θ Sun > 55 o. March 2005 - September 2008: 148 bursts 75% optical/near-IR afterglows 45% afterglow-based spectroscopic redshifts

9. Redshifts from optical afterglow spectroscopy High or medium resolution is preferred as much more information is available. But most OAs are too faint for high-res spectroscopy with available spectrographs

10. Elíasdóttir et al. (2009); Krühler et al. (2008) X-shooter spectrum revealing emission lines from the host (M. Sparre)   FORS spectrum of the afterglow with 2175 Å extinction bump (z=2.45, A V ~1mag) 

11. Zafar et al. (2011,2012) X-shooter spectrum of the host  SFR = 30 M  /yr Oxygen abundance 40-110% solar Krühler et al. (2012)  Afterglow derived extinction curve with 2175 Å extinction bump (z=1.65, A V =0.5 mag) 

12. GRB080607 Spectroscopy started 20 min post burst – Bloom and Perley R>24 when observable from La Palma (12 hr later) GRB070306 Prochaska et al. (2009) Keck z = 3.04 logN HI =22.7 H 2 and CO Forest of metal lines! Solar metallicity A V =3.3 mag 2175Å extinction bump. Bright/massive and dusty host SFR = 10 M  /yr Imagine E-ELT

13. GRB090323 GRB070306 Savaglio et al. (2012) VLT/FORS z = 3.57 logN HI =20.7 Super-solar metallicity A V =0.1-0.2 mag

14. GRB120815A Spectroscopy started 1.67 hr post burst GRB070306 Krühler, Ledoux, Fynbo, et al. in prep (2012) VLT / X-shooter (40 min exp.) z = 2.358 logN HI =22.1 H 2 Low metallicity A V ≈0.2 mag No 2175Å extinction bump. Tentative detec. host emisson lines.

15. GRB07306, z=1.50, VLT, strong reddening, but blue host. Jaunsen et al. 2008 GRB070306 Jaunsen et al. (2008)

16. Metallicities (Examples from X-shooter GTO) D’Elia et al. (2010), Thöne et al. (2012); Sparre et al. in prep.; D’Elia et al., in prep; Savaglio et al (2012)

17. An instrument that will allow a spectroscopic study of the underrepresented faint, dusty, metal- and likely molecular-rich GRB sightlines. Specs: ideally 3200-24000 Å, high efficiency (need to reach AB>22), R>10000, AO assisted where possible to gain the depth The blue/near-UV is important (HI, H 2 ). Rather loose K and the blue. Decent flux calibration RRM/ToO observing mode

18. GRB090926A SFR = <2 M  /yr [S/H] = -1.9 D’Elia et al. (2010)

19. The mean escape fraction of UV photons from star- forming galaxies: f escape <7% (95% confidence) Chen et al. (2007); Fynbo et al. (2009)

20. DLA at z=2.354 towards Q2222-0946 [Zn/H]=-0.46, SFR=20M  /yr

21. z=2.58 DLA towards Q0918+1636: [Zn/H]=-0.12, H 2, CI, SFR≈20M  /yr