Can We Search for the First Stars Using GRBs?

Susumu Inoue (Kyoto U.)

- signature of Pop III stars- Pop III -> II transition

“A long-standing problem has been put to rest.”K. Omukai, apparently distinguished professor

“A long-standing theoretical problem has been put to rest.”

To solve a scientific problem,experimental (observational) tests are necessary!

first star epoch

Yoshida, Omukai & Hernquist 08

z~100-10Pop 3=metal/dust-free, H2+HD-cooling

assume: no metal/dust, B field, CR, turbulence, DM heating

(1st generation) massive, high UV1st HII region -> IGM reionization1st SN -> 1st metal/dust (+CR+B)

(2nd generation)

Pop 3.1

Pop 3.2not-so-massive?

Pop 2=metal/dust-cooling1st sun -> 1st planet, life, human!

1st BH -> 1st QSO

need to be tested observationally!

when and how?need observations

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Pop 3 (~Myr ) → Pop 2 (~Gyr)transition: beginning of life?

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wikipedia article

Pop 3 → Pop 2 transition

Omukai+ 05 model

[Z/H]<-6: Mfrag~103M Pop 3-3<[Z/H]<-5: Mfrag~0.1-100M Pop 2

[Z/H]crit=-5+-1

H2

H2+HDdust

T minimum -> fragmentationcollapsing zero/low-metal. protostellar clouds

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What is a “first star”?

first Pop 3 stars are (probably) characterized by:- very high to high redshift z~60-5?- very low metals/dust Z/Z~<10-5?- very massive M/M>few x100?

- luminous UV -> large HII region?- weak wind -> clean environment?? - GRB progenitors?

Mamma,che cosa è unaprima stella?

Allora,tesorina…

uncertain but probablelet’s assume for now

upper limits on Pop 3 stars

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slide from T. Nagao

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THE very first GRB Naoz & Bromberg 07

peak energy ~few keV (XRF)long duration ~1000s

z~60-30?

1054 erg/s

1053

1052

Swiftdetectability

expected GRB rate

high-z GRB afterglows c.f. SI, Omukai & Ciardi

2007 MNRAS 380, 1715

GRBs are:very brightvery broadband (<GHz-GeV<)

-32

-30

-28

-26

-24

161412108 log ν [Hz]

z=1

t=1 day

5

30

tiνt=8hr, 5σ σeνσitivitieσ

10

ALMA

VLA

EVLA

SKA

Spitzer

60

SPICA

Subaru

BUT transient

very high z

c.f. SI, Omukai & Ciardi 2007 MNRAS 380, 1715

JWST, SPICA

z~60-20 (Ly break >3-7 m)

z>~20 space instruments

: Ly break spectroscopy in mid IR

crude, quick z indicatorsalso useful

-32

-30

-28

-26

-24

15.515.014.514.013.513.0

log ν [Hz]

z=1

t=1 day

5

30

R=100, tiνt=3 hr, S/N=10 σeνσitivity

Ly a

10

60

Subaru

TMT+AO

JWST 20

Compton attenuation in IGM

concordance universeCompton thick at z>~56

z

tT

E>~keV indep. of ionizationE>~MeV Klein-Nishina decline

attenuated spectrum

log E [MeV]

log νFν

star formation with first dust Schneider+ 06

PISN Z=0 SNII

absorption by first dust

Schneider+ 06

(optical depth at fragmentation)

or even marginal Pop 3 ([Z/H]~<10-5) observable?

If such dust-cooling cores exist near a GRB:

also depends on first dust properties other metal lines?

effects of Pop 3 -> Pop 2 transition

very low metals/dust

column density of first protostellar cores

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log(Z/Z)

log

N H,f

rag

Yoshida+ 08

at low metallicity, highly Compton-thick tT>>1

Does all the core material accrete onto the star? May be not.

column densityat fragmentationvs metallicity

If not, is the remaining material swept out by the HII region? How far?Can dust and/or molecules survive destruction in such material?

By the end of the progenitor’s life:

GRBs in Compton thick environments

tT=0, 0.1, 0.3,1,10,30,100central point source in spherefollowing Sunyaev & Titarchuk 80

Compton downscattering

log(E/mec2)

log(

νfν)

- spectral softening- duration lengthening- variability smearing

c.f. Compton-thick AGNs

possible Pop3 signature?

Pop 3 HII regions

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Whalen+ 04

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- large r~<100 pc- low density n~0.1 cm-3

Can be probed throughafterglow evolution?

- flat profile

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Pop 3 HII regions

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Kitayama+ 04

Mstar=200M

Mhalo=106MMhalo=107M

depends on halo environment

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dust distribution in GRB environment

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rdest

GRB

dust

foreground star forming cores

GRB

star forming cores triggered byphotodiss. region driven shock

caveats:dust-cooled fragments -> not GRB progenitors?

Tsuribe & Omukai 06

effect of progenitor evolution: UV, HII region, wind …destruction by GRB UV+X

Questions to Pop 3 theorists

Q1. How much core material is remaining in the vicinityof the star (e.g. ~< pc) at the end of its life?

Q2. How much dust (or molecules) are remainingin such material?

If significant, Compton attenuation of prompt emission?

Summary and Outlook

GRBs are likely observable out to very high z (~60)

In any case, density profile can be probed throughafterglow evolution?

If significant, very low (critical) metallicity observable?

first dust from first supernovae

Maiolino+ 04Todini & Ferrara+ 01also Nozawa+ 03, 06, 07

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Schneider+ 06

SiO2

Mg2SiO4

AC

ACPISN

Z=0 SNII

less formation time, smaller grains→ more efficient coolant flatter extinction curve (matches QSO obs.?)

⇔ today’s dust from AGB

QSO z=6

but destruction by reverse shock?

PISN

Schneider+ 04