Palli Jakobsson Astronomical Observatory University of Copenhagen

1. The line-of-sight towards GRB030429 at z=2.66: Probing matter at stellar,galactic and intergalacticscales Palli Jakobsson Astronomical Observatory University of Copenhagen Padova 21 April 2004

2. Main Collaborators Jens Hjorth (AO, Copenhagen) Johan Fynbo (Århus Univ.) Michael Weidinger (Århus Univ.) Darach Watson (AO, Copenhagen) Javier Gorosabel (STScI, Baltimore) Kristian Pedersen (AO, Copenhagen) Cedric Ledoux (ESO, Santiago) Gulli Björnsson (Science Institute, Reykjavík) Ralph Wijers (Astronomical Institute, Amsterdam) GRACE

3. Outline Burst environment: playing the (α,β,p)-game Host galaxy (DLA): dust-to-gas ratio Mg II absorber along the line-of-sight: very small impact parameter, D = 1.2” Strong gravitational lensing?

4. Imaging of GRB 030429 • A galaxy only 1.2” away from the • host  initially considered to be • a probable host galaxy. • VLT spectroscopy soon showed: • zGRB = 2.66 • zgalaxy = 0.84 • Initially a 1’ error radius circulated • Limiting magnitude from a GCN: • >20 mags at 1.9 hours • Fulfilled our ”dark burst” criteria • 6 VLT epochs in R & VRIJK • during 2 epochs • A week later: correct error radius • had actually been 2’

5. Spectral Energy Distribution K J I R V 000301C 000926 021004 011211 020124 Best fit with SMC: β = -0.36 ± 0.12 and AV = 0.34 ± 0.04

6. Light Curves Electron energy power-law index p(β) = 1.72 ≠ p(α2) = 3.46

7. Burst Environment • Closure relation (Price et al. 2002): only a jet • expanding into a wind-stratified medium works • For the fireball model to be consistent, a bright • long-lived (2-3 days) bump must bepresent in the • GRB 030429 light curve • Achromatic light curve behaviour

8. The Host Galaxy A zoom in on the Lyα line from the VLT OA spectrum: Log N(H I) = 21.6 ± 0.1  Damped Lyα Absorber (DLA)

9. The Host Galaxy • A high value of the ratio between N(H I) and the • optical extinction • N(H I)/E(B-V) = (34 ± 9) ∙ 1021 cm-2 mag-1 • Fully consistent with SMC (metal-poor)

10. The Mg II Absorber • At zgalaxy = 0.84, 1.2” corresponds to an impact • parameter of only D = 9 kpc • In the ”QSO-business” D is frequently • interpreted as the lower limit of the radii of • suspected counterparts of absorption- • selected galaxies • At a redshift of ~1, the majority of counterparts • are thought to have D > 50 kpc

11. The Mg II Absorber • The real absorber could be very faint and/or • hidden inside the glare of the QSO  • overestimating the counterpart radius • Possible to test this with OAs, they are high-z, • and fade away completely within a few months • All evidence from OAs suggests that D is indeed • much smaller: Of the 6 GRBs that have Mg II • absorption systems (besides the one produced in • the host galaxy) in their OA spectra, at least 4 of • them have nearby galaxies at 1”-4” (5-20 kpc)

12. Strong Gravitational Lensing? There are at least 2 facts that make it improbable: • The Einstein radius has to be at least • as large as the impact parameter. This • corresponds to a mass of >5.4 · 1011 Msun. • At zgalaxy = 0.84, 1.2” corresponds to 9 kpc, • so this mass is roughly 6 times larger than • for Milky-Way like galaxies. • For the OA-galaxy configuration, the critical • surface mass density is 0.43 g cm-2, around • 3-4 times larger than in normal galaxy lenses

13. Summary • Shaped by the stellar wind of a massive • star progenitor. Density? Refreshed • shocks? Jet structure? Microlensing? Progenitor environment • A DLA with a dust-to-gas ratio fully • consistent with that of the SMC. The SED • also consistent with an SMC-like • extinction law. Host galaxy • Small impact parameter in contrast to • identifications of most QSO absorption- • selected galaxy counterparts. Mg II absorber • Afterglow appearance not affected by • the nearby galaxy. Strong lensing