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~ Pop 3 =metal/dust-free, H 2 +HD-cooling assume: no metal/dust, B field, CR, turbulence, DM heating (1st generation) massive, high UV 1st HII region -> IGM reionization 1st SN -> 1st metal/dust (+CR+B) (2nd generation) Pop 3.1 Pop 3.2 not-so-massive? Pop 2 =metal/dust-cooling 1st sun -> 1st planet, life, human! 1st BH -> 1st QSO need to be tested observationally! when and how? need observations

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

Pop 3 → Pop 2 transition Omukai+ 05 model [Z/H]<-6: M frag ~10 3 M  Pop 3 -3<[Z/H]<-5: M frag ~ M  Pop 2 [Z/H] crit =-5+-1 H2H2 H 2 +HD dust T minimum -> fragmentation collapsing zero/low-metal. protostellar clouds

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 una prima stella? Allora, tesorina… uncertain but probable let’s assume for now

upper limits on Pop 3 stars slide from T. Nagao

THE very first GRB Naoz & Bromberg 07 peak energy ~few keV (XRF) long duration ~1000s z~60-30? erg/s Swift detectability expected GRB rate

high-z GRB afterglows c.f. SI, Omukai & Ciardi 2007 MNRAS 380, 1715 GRBs are: very bright very broadband (<GHz-GeV<) 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 indicators also useful

Compton attenuation in IGM concordance universe Compton thick at z>~56 z TT E>~keV indep. of ionization E>~MeV Klein-Nishina decline attenuated spectrum log E [MeV] log F

star formation with first dust Schneider+ 06 PISNZ=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 log(Z/Z  ) log N H,frag Yoshida+ 08 at low metallicity, highly Compton-thick  T >>1 Does all the core material accrete onto the star? May be not. column density at fragmentation vs 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  T =0, 0.1, 0.3,1,10,30,100 central point source in sphere following Sunyaev & Titarchuk 80 Compton downscattering log(E/m e c 2 ) log( f ) - spectral softening - duration lengthening - variability smearing c.f. Compton-thick AGNs possible Pop3 signature?

Pop 3 HII regions Whalen large r~<100 pc - low density n~0.1 cm -3 Can be probed through afterglow evolution? - flat profile

Pop 3 HII regions Kitayama+ 04 M star =200M  M halo =10 6 M  M halo =10 7 M  depends on halo environment

dust distribution in GRB environment r dest GRB dust foreground star forming cores GRB star forming cores triggered by photodiss. 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 vicinity of the star (e.g. ~< pc) at the end of its life? Q2. How much dust (or molecules) are remaining in 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 through afterglow evolution? If significant, very low (critical) metallicity observable?

first dust from first supernovae Maiolino+ 04 Todini & Ferrara+ 01 also Nozawa+ 03, 06, 07 Schneider+ 06 SiO 2 Mg 2 SiO 4 AC PISN 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