Probing Massive Star-forming Probing Massive Star-forming Regions Using GRB AfterglowsRegions 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– 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.

Massive star-forming region in the MW

Carinae nebula (d~2.3 kpc)

Carinae star

HDE303308CPD-59D2603

n H > 107 cm-3

Te = 760-6400 K(Gull+05)n H < 104 cm-3

(Walborn+02;Gull+05)

1.5 pc

UV spectroscopyreveals circumstellar gas

at r ~ 1000 AU

GRB050730GRB050730 at z=3.968 at z=3.968 (Magellan/MIKE)(Magellan/MIKE)

Chen et al. (2005)

RRpeakpeak ~ 14 ~ 14

Host-DLA at z = 3.968N (HI) = 1022.15 cm-2

f ~ 1.88

Classical DLA

‘additional’

GRB050730GRB050730 at z=3.968 at z=3.968 (Magellan/MIKE)(Magellan/MIKE)

Chen et al. (2005)

Heavy elements observed in the ISM of the host

• [S / H] = -2.0[S / H] = -2.00.10.1• [S / Fe] = 0.3[S / Fe] = 0.3•vv ~ 20 km/s ~ 20 km/s

GRB050820 at z = 2.61 GRB050820 at z = 2.61 (Keck/HIRES)(Keck/HIRES)

Prochaska et al. (2006)

Heavy elements observed in the ISM of the host

• log log N N (HI)=21(HI)=21• [S / H] = -0.6[S / H] = -0.60.10.1• [S / Fe] = 1.0[S / Fe] = 1.0•vv ~ 50 km/s ~ 50 km/s

GRB051111 at z = 1.55 GRB051111 at z = 1.55 (Keck/HIRES)(Keck/HIRES)

Prochaska et al. (2006)

Heavy elements observed in the ISM of the host

• [Si / H] > -2.8[Si / H] > -2.8• [Si / Fe] > 0.8[Si / Fe] > 0.8•vv ~ 30 km/s ~ 30 km/s

GRB060418 at z=1.49GRB060418 at z=1.49 (Magellan/MIKE)(Magellan/MIKE)

Heavy elements observed in the ISM of the host

ISM Properties of the GRB Hosts

• High column density gas• Abundant excited ions (e.g. O0, C+, Si+,

Fe+)• Sub-solar metallicity• -element enhancement• Absence of neutral species (e.g. C0, S0,

Fe0)• Lack of molecular gas

GRB050730 Characteristic of Boltzman Function!!

GRB051111GRB060418

Excitation MechanismExcitation Mechanism

Population ratio between excited FeII states

• Collision?• Photon pumping?

implied gas densitynH

> 106 cm-3

CaveatsCaveats::• high high nnHH,,

missing Cmissing C00, Fe, Fe00, etc., etc.• high high P = nkTP = nkT, , small small vv ~ 20 km/s ~ 20 km/s

Prochaska, Chen, & Bloom (2006)

Mg0

G0 = 1.6 x 10-3 erg cm-2 s-1

Excitation MechanismExcitation Mechanism

Indirect UV pumpingIndirect UV pumping:

• Collision?• Photon pumping?

x

naturally explains all observationsnaturally explains all observations

Discriminating Tests:Discriminating Tests:

ObservationObservationUV UV

pumpingpumpingCollisionsCollisions

NJ=3/2(Fe+) = 2 N J=1/2(Fe+) Required ne >104, T >2500 K

Inverted Fe+ population Ruled out ne <103

Variability Variability ExpectedExpected Ruled outRuled out

Absence of neutral speciesAbsence of neutral species ExpectedExpected Challenging Challenging

Overabundance of FeOverabundance of Fe++ J=9/2J=9/2 ExpectedExpected Challenging Challenging

GRB Progenitor EnvironmentGRB Progenitor Environment

Ionized (Circumstellar?) GasIonized (Circumstellar?) GasNo neutral gasNo neutral gas

0.05pc<1pc~100pc 80pc~500pc

HI cloudHI cloud

SFR Gas?SFR Gas?All of the FeII, SiII, MgIAll of the FeII, SiII, MgI

Optical depth effects limit FeII*, SiII*Optical depth effects limit FeII*, SiII*

Classical vs. GRB Host DLAsClassical vs. GRB Host DLAs: : low low metal?metal?

Erb et al. (2006)

Tremonti et al. (2004)

SDSS at z ~ 0.1

LBG’s at z ~ 2