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Probing Massive Star-forming Regions Using GRB Afterglows

Probing Massive Star-forming Regions Using GRB Afterglows. Hsiao-Wen Chen (University of Chicago) ~ The GRAASP Collaboration ~ Josh Bloom (UC Berkeley) Jason X. Prochaska (UC Santa Cruz). Background:. Source/Location

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Probing Massive Star-forming Regions Using GRB Afterglows

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  1. Probing Massive Star-forming Regions Using GRB Afterglows Hsiao-Wen Chen (University of Chicago) ~ The GRAASP Collaboration ~ Josh Bloom (UC Berkeley) Jason X. Prochaska (UC Santa Cruz)

  2. Background: • Source/Location • The origin of long-duration GRBs is now well established in the death of massive stars. • Afterglow spectroscopy • Absorption-line studies of intervening gas, e.g. gas density, kinematics, and chemical composition, along the line of sight.

  3. Carinae star HDE303308 CPD-59D2603 Massive star-forming region in the MW n H > 107 cm-3 Te = 760-6400 K (Gull+05) n H < 104 cm-3 (Walborn+02;Gull+05) UV spectroscopy reveals circumstellar gas at r ~ 1000 AU 1.5 pc h Carinae nebula (d~2.3 kpc)

  4. GRB050730 at z=3.968 (Magellan/MIKE) Rpeak ~ 14 Classical DLA Host-DLA at z = 3.968 N (HI) = 1022.15 cm-2 ‘additional’ fn ~ l1.88 Chen et al. (2005)

  5. Chen et al. (2005) GRB050730 at z=3.968 (Magellan/MIKE) Heavy elements observed in the ISM of the host • [S / H] = -2.00.1 • [S / Fe] = 0.3 • Dv ~ 20 km/s

  6. GRB050820 at z = 2.61 (Keck/HIRES) Heavy elements observed in the ISM of the host • log N (HI)=21 • [S / H] = -0.60.1 • [S / Fe] = 1.0 • Dv ~ 50 km/s Prochaska et al. (2006)

  7. GRB051111 at z = 1.55 (Keck/HIRES) Heavy elements observed in the ISM of the host • [Si / H] > -2.8 • [Si / Fe] > 0.8 • Dv ~ 30 km/s Prochaska et al. (2006)

  8. GRB060418 at z=1.49 (Magellan/MIKE) Heavy elements observed in the ISM of the host

  9. ISM Properties of the GRB Hosts • High column density gas • Abundant excited ions (e.g. O0, C+, Si+, Fe+) • Sub-solar metallicity • a-element enhancement • Absence of neutral species (e.g. C0, S0, Fe0) • Lack of molecular gas

  10. Characteristic of Boltzman Function!! GRB050730 GRB051111 GRB060418 • Collision? • Photon pumping? Excitation Mechanism Population ratio between excited FeII states implied gas density nH> 106 cm-3 • Caveats: • high nH, • missing C0, Fe0, etc. • high P = nkT, • small Dv ~ 20 km/s

  11. x Mg0 • Collision? • Photon pumping? Excitation Mechanism Indirect UV pumping: naturally explains all observations G0 = 1.6 x 10-3 erg cm-2 s-1 Prochaska, Chen, & Bloom (2006)

  12. Discriminating Tests:

  13. GRB Progenitor Environment SFR Gas? All of the FeII, SiII, MgI Optical depth effects limit FeII*, SiII* Ionized (Circumstellar?) Gas No neutral gas HI cloud ~500pc ~100pc 80pc <1pc 0.05pc

  14. SDSS at z ~ 0.1 LBG’s at z ~ 2 Tremonti et al. (2004) Erb et al. (2006) Classical vs. GRB Host DLAs: low metal?

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