Studying GRB Studying GRB Environments and Environments and Progenitors with Progenitors with

Absorption Spectroscopy Absorption Spectroscopy

Studying GRB Studying GRB Environments and Environments and Progenitors with Progenitors with

Absorption Spectroscopy Absorption Spectroscopy

Derek B. FoxAstronomy & Astrophysics

Penn State University

Image: Aurore Simonnet, Sonoma State

Group Papers1. 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.

2. 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.

3. 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.

4. 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.

5. 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 A High-Velocity Wind Around a Massive Star at Around a Massive Star at

z=4.27z=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.

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2006a

GRB 050505

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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

Berger et al. 2006a

Dense Excited Gas Near a Dense Excited Gas Near a Massive Star at z=1.55Massive 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

Penprase et al. 2006

Penprase et al. 2006

Penprase et al. 2006

Penprase et al. 2006

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 The Environment and Host Galaxy of a Massive Host Galaxy of a Massive

Star at z=6.3Star 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

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QuickTime™ and aTIFF (LZW) decompressor

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6log NHI=21.6

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Berger et al. 2006c

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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

Frail et al. 2006

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

ConclusionsConclusions

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 SpectroscopyHigh-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 SpectroscopyExcited 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 EndThe End

Image: Aurore Simonnet, Sonoma State