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Studying GRB Environments and Progenitors with Absorption Spectroscopy. Derek B. Fox Astronomy & Astrophysics Penn State University. Image: Aurore Simonnet, Sonoma State. Group Papers.
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Studying GRB Environments and Progenitors with Absorption Spectroscopy Derek B. Fox Astronomy & Astrophysics Penn State University Image: Aurore Simonnet, Sonoma State
Group Papers • Spectroscopy of GRB 050505 at z=4.275: A log N(HI)=22.1 DLA Host Galaxy and the Nature of the Progenitor. Berger et al. 2006a, ApJ submitted, astro-ph/0511498. • Fine-Structure FeII and SiII Absorption in the Spectrum of GRB 051111: Implications for the Burst Environment.Berger et al. 2006b, ApJL submitted, astro-ph/0512280. • Spectroscopy of GRB 051111 at z=1.54948: Kinematics and Elemental Abundances of the GRB Environment and Host Galaxy.Penprase et al. 2006, ApJ in press, astro-ph/0512340. • HST and Spitzer Observations of the Host Galaxy of GRB 050904: A Metal-Enriched Dusty Starburst at z=6.295.Berger et al. 2006c, ApJ submitted, astro-ph/0603689. • An Energetic Afterglow from a Distant Stellar Explosion.Frail et al. 2006, ApJ submitted, astro-ph/0604580.
Group Members • Edo Berger, Mike Gladders & Pat McCarthy (Carnegie) • Bryan Penprase (Pomona) • Dale Frail (NRAO) • Shri Kulkarni, S. Brad Cenko, Alicia Soderberg, Ehud Nakar,Eran Ofek, Avishay Gal-Yam, Mansi Kasliwal, P. Brian Cameron, Chuck Steidel, Naveen Reddy & S. George Djorgovski (Caltech) • Paul Price & Len Cowie (IfA Hawaii) • Brian Schmidt &Bruce Peterson (MSO/ANU) • Derek Fox (Penn State) • Ranga-Ram Chary (Spitzer) • Amy Barger (Wisconsin) • Grant Hill, Barbara Schaefer & Marilyn Reed (Keck)
Long GRBs as Massive Stars • GRB-Supernova = “Gamma-Ray Bright Supernova” • SN Ic – No Hydrogen – Wolf-Rayet progenitor • What makes a star go GRB? (What makes a star go SN?) • Massive Stellar Autopsy: • Redshift • Energetics • Circumburst material • Nickel mass (low-z) • Multimessenger astronomy (very low-z) • Rare population = Biases likely (low-Z? binaries?) Stanek et al. 2003
GRB Afterglow Spectroscopy • Uniquely bright sources at cosmological distances • Illuminate immediate burst surroundings • W-R Winds • Mass ejection events • Occur in the midst of a host galaxy • Host observed as DLA • Rich array of metal lines • What are the conditions of massive star formation at z>1? • At z>4? • At z>6?
GRB Afterglow Spectroscopy • Uniquely bright sources at cosmological distances • Illuminate immediate burst surroundings • W-R Winds • Mass ejection events • Occur in the midst of a host galaxy • Host observed as DLA • Rich array of metal lines • What are the conditions of massive star formation at z>1? • At z>4? • At z>6? 56% complete Jakobsson/Swift sample
A High-Velocity Wind Around a Massive Star at z=4.27 • Spectroscopy of GRB 050505 at z=4.275: A log N(HI)=22.1 DLA Host Galaxy and the Nature of the Progenitor. Berger et al. 2006a, ApJ submitted, astro-ph/0511498.
GRB 050505 Berger et al. 2006a
Nature of the Absorbers • Highest-column DLA known • Composite curve of growth indicates small velocity spread, ~100 km s–1 • Dust depletion analysis disfavors cold disk • Si II* detection implies high density material, nH > 102 cm–3 • 1000 km s–1 velocity spread for C IV but not Si IV • Either a local or galaxy-scale wind Berger et al. 2006a
Nature of the Absorbers • Highest-column DLA known • Composite curve of growth indicates small velocity spread, ~100 km s–1 • Dust depletion analysis disfavors cold disk • Si II* detection implies high density material, nH > 102 cm–3 • 1000 km s–1 velocity spread for C IV but not Si IV • Either a local or galaxy-scale wind Berger et al. 2006a
Nature of the Wind • Reminiscent of multiple C IV systems to –3000 km s–1 in GRB 021004 (resolved) • GRB 021004 structure identified in H I, other less-ionized species • Led to clumpy wind models • Implies an enrichment of [C/Si] in the progenitor stellar wind for GRB 050505 • Winds from LBGs can reach 1000 km s–1, however… Berger et al. 2006a
GRB Hosts v. QSO DLAs • GRB hosts extend to higher HI column densities • Metallicities higher for a given redshift • Si II* never seen in line-of-sight DLAs • Implies small cross-section for Si II* systems • Consistent with high inferred densities, nH >~ 102 cm–3 Berger et al. 2006a
Dense Excited Gas Near a Massive Star at z=1.55 • Fine-Structure Fe II and Si II Absorption in the Spectrum of GRB 051111: Implications for the Burst Environment.Berger et al. 2006b, ApJL submitted, astro-ph/0512280. • Spectroscopy of GRB 051111 at z=1.54948: Kinematics and Elemental Abundances of the GRB Environment and Host Galaxy.Penprase et al. 2006, ApJ in press, astro-ph/0512340. And see also: • Dissecting the Circumstellar Environment of GRB Progenitors. Prochaska, Chen & Bloom 2006, ApJ submitted, astro-ph/0601057
Nature of the Absorbers • Log N(HI) ~ 21.9 via Zn II • Velocity spread ~10 km s–1 from curve of growth • Dust depletion analysis favors warm disk • Excited states to Fe II****, Si II* from high-density material on line of sight • What is the source of this excitation? Penprase et al. 2006
Nature of the Absorbers • Log N(HI) ~ 21.9 via Zn II • Velocity spread ~10 km s–1 from curve of growth • Dust depletion analysis favors warm disk • Excited states to Fe II****, Si II* from high-density material on line of sight • What is the source of this excitation? Penprase et al. 2006
Nature of the Excitation • Collisional excitation could explain FeII* states alone, but inconsistent with Si II* • Radiative excitation is thus preferred • If it is the GRB/afterglow, time-dependent absorption features are expected • Otherwise the IR radiation field with F ~ 2.2might be supplied by a nearby supercluster Berger et al. 2006b
The Environment and Host Galaxy of a Massive Star at z=6.3 • HST and Spitzer Observations of the Host Galaxy of GRB 050904: A Metal-Enriched Dusty Starburst at z=6.295.Berger et al. 2006c, ApJ submitted, astro-ph/0603689. • An Energetic Afterglow from a Distant Stellar Explosion.Frail et al. 2006, ApJ submitted, astro-ph/0604580. Along with: • Implications for the Cosmic Reionization from the Optical Afterglow Spectrum of the Gamma-Ray Burst 050904 at z=6.3. Totani et al. 2006, PASJ submitted, astro-ph/0512154
GRB 050904 • Swift XRT position (6 arcsec) • Deep optical limits from P60 • Bright NIR afterglow with SOAR: z > 6 (Haislip et al. 2006) • Detection with a 0.5-m optical telescope… (TAROT; Gendre et al. 2006) • Subaru redshift, z=6.3 (Kawai et al. 2006; Totani et al. 2006) • DLA prevents strong constraints on HI in the IGM • Host metallicity ~ 5% solar Haislip et al. 2006
log NHI=21.6 Totani et al. 2006
Nature of the Host Galaxy • Metallicity of ~5% solar (Kawai et al. 2006) • MUV ~ –21.7 mag • L ~ L* for this redshift • SFR ~ 15 M yr–1 • Extension of the mass-metallicity relationship to z=6.3 • Galaxy metallicities continue to decrease with redshift… Berger et al. 2006c
Nature of the Environment • Extremely energetic burst: E ~ 1052 ergs, including jet correction • Roughly x30 greater energy than z~1 GRBs • Density n ~ 700 cm–3 • Roughly x100 greater density than z~1 GRBs • Consistent with density of the Si II* absorber (Kawai et al. 2006) Frail et al. 2006
Conclusions Image: Aurore Simonnet, Sonoma State
GRB Afterglow Spectroscopy • GRBs are a merciless probe of their surroundings • Host is usually a DLA • Velocity broadening mild in most species • Metal abundances >~typical for GRB redshift • Host DLA + metals complicate z>6 IGM studies (Totani et al. 2006) • Unusual features: • High-velocity absorption systems • Excited states of Si, Fe
GRB Afterglow Spectroscopy High-Velocity Absorption: • Stellar wind is the readiest source of v ~ 1000 km s–1 metals on line of sight • But: LBGs also exhibit v > 300 km s–1 outflows • No temporal changes in absorption features have been detected Berger et al. 2006a
GRB Afterglow Spectroscopy Excited states of Si, Fe: • Si II* allows a direct estimate of the density of the absorber • n > 100 cm–3 @ z=4.3 • n ~ 300 cm –3 @ z=6.3 • High local density for GRB 050904 confirmed by radio detection + afterglow model • Fe II* states probably not due to collisional excitation • Radiative pumping may be due to strong ambient IR light or the effect of the GRB/afterglow • Afterglow effects will produce varying absorption features Berger et al. 2006b
The End Image: Aurore Simonnet, Sonoma State