Studying GRB Environments and Progenitors with Absorption Spectroscopy Derek B. Fox Astronomy & Astrophysics Penn State University Image: Aurore Simonnet, Sonoma State

Group Papers 1.Spectroscopy of GRB 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/ Fine-Structure FeII and SiII Absorption in the Spectrum of GRB : Implications for the Burst Environment. Berger et al. 2006b, ApJL submitted, astro-ph/ Spectroscopy of GRB at z= : Kinematics and Elemental Abundances of the GRB Environment and Host Galaxy. Penprase et al. 2006, ApJ in press, astro-ph/ HST and Spitzer Observations of the Host Galaxy of GRB : A Metal-Enriched Dusty Starburst at z= Berger et al. 2006c, ApJ submitted, astro-ph/ An Energetic Afterglow from a Distant Stellar Explosion. Frail et al. 2006, ApJ submitted, astro-ph/

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 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/

Berger et al. 2006a GRB

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, n H > 10 2 cm – 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, n H > 10 2 cm – 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 (resolved) GRB 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 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, n H >~ 10 2 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 : Implications for the Burst Environment. Berger et al. 2006b, ApJL submitted, astro-ph/ Spectroscopy of GRB at z= : Kinematics and Elemental Abundances of the GRB Environment and Host Galaxy. Penprase et al. 2006, ApJ in press, astro-ph/ And see also: Dissecting the Circumstellar Environment of GRB Progenitors. Prochaska, Chen & Bloom 2006, ApJ submitted, astro-ph/

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 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 ~ 2.2 might 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 : A Metal-Enriched Dusty Starburst at z= Berger et al. 2006c, ApJ submitted, astro-ph/ An Energetic Afterglow from a Distant Stellar Explosion. Frail et al. 2006, ApJ submitted, astro-ph/ Along with: Implications for the Cosmic Reionization from the Optical Afterglow Spectrum of the Gamma-Ray Burst at z=6.3. Totani et al. 2006, PASJ submitted, astro-ph/

GRB 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

Totani et al log N HI =21.6

Berger et al. 2006c

Nature of the Host Galaxy Metallicity of ~5% solar (Kawai et al. 2006) M UV ~ –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

Frail et al. 2006

Nature of the Environment Extremely energetic burst: E ~ 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 z=4.3 –n ~ 300 cm z=6.3 High local density for GRB 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