Long Gamma Ray Bursts from metal poor/pop III stars. Sung-Chul Yoon (Amsterdam) Norbert Langer (Utrecht) Colin Norman (JHU/STScI)

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1 Long Gamma Ray Bursts from metal poor/pop III stars Sung-Chul Yoon (Amsterdam) Norbert Langer (Utrecht) Colin Norman (JHU/STScI) The First Stars and Evolution of the Early Universe, Seattle, June 06, 2006

2 Progenitors of long GRBs Some clues that long GRBs are associated with deaths of massive stars Association with star-forming regions in galaxies GRB SN 1998bw GRB SN 2003dh GRB SN 2006aj All long GRBs are related to BH forming supernovae/hypernovae? (cf. talk by Nomoto) Observable from high z (z > 10; currently up to z ~ 6.29) Tracer of star formation at high z? GRBs from first stars?

3 Necessary Conditions for long GRB production from massive stars according to the collapsar scenario (Woosley) He core massive enough to form BH Rapid rotating core (Formation of relativistic Jets; Collapsar scenario by Woosley formation of a Keplerian disk around a black hole: j > cm 2 /s) Removal of H envelope Difficult at very low metallicity (?) => but we observe GRBs from low metallicity environments. (e.g. GRB host galaxy has 12+log(O/H) = ~ 7.54; Wiersema et al. 06) => All GRBs are from metal poor stars?

4 Models of rotating massive stars (Meynet, Maeder, Hirschi, Heger, Langer, Woosley, Yoon) Without B-fields Eddington Sweet Circulations/ Shear instability Strongly differential rotation throughout the evolution At low Z, mixing is dominated by the shear instability during the giant phase. Strong mass loss (and thus WR star formation) is possible due to the surface enrichment of CNO elements during the giant phase (cf. the talk by G. Meynet). With B-fields Magnetic torques (Spruit 00) Nearly rigid rotation on main sequence Weak differential rotation during the giant phase Mixing is dominated by ES circulations. Chemically homogeneous evolution with very high initial J?

5 Models of rotating massive stars Maeder & Meynet (2005) Non-magnetic models The core keeps large amounts of angular momentum (Heger, Langer, Woosley 00; Hirschi, Meynet & Maeder 05) Magnetic models ( with Spruit Tayler dynamo; Spruit 2000) The core loses a lot of angular momenta (Heger, Woosley & Spruit 05; Maeder & Meynet 05)

6 Spin down of the core by magnetic braking

7 Role of magnetic torques in J-transport Models with B-fields are more consistent with observed spin rates of stellar remnants and some other aspects. Observations Models without B- fields Models with B-fields (Spruit- Talyer dynamo) Young NS spin ms < 1ms (Heger et al.00; Hirschi et al. 05) 4 15 ms (Heger et al. 05; Ott et al. 06) WD spin < 10 km/s ~ 150 km/s (Langer et al. 98) < 10 km/s (Suijs et al. 05) Sun Rigid rotation in the core Differential rotation Rigidly rotating core (Eggenberger et al. 05) RGRB/ RSNIbc GRBs are rare! Too high! Difficult to make GRBs from normal type of evolution

8 Evolution of metal poor massive stars (with B-fields) Less mass loss : Mdot ~ Z (talk by J. Vink) Good for keeping angular momentum (but the core is still spun down by magnetic torques) Bad for making Wolf-Rayet stars Keep more angular momentum => more chemical mixing? ted ~ tth/[ω/ωk]

9 Bifurcation in massive star evolution according to initial spin rate (originally suggested by Maeder 87) Yoon & Langer 05, 06 Woolsey & Heger 06

10 Quasi-chemically homogeneous evolution Minit = 16 Msun, Z = tms < tmix tms > tmix Vinit/VK = 0.3. Vinit/VK = 0.6 Yoon & Langer (05, 06); Woosley & Heger (06)

11 Quasi-chemically homogeneous evolution Normal evolution Chemically homogeneous evolution

12 Evolution of massive stars at low metallicity Final Fate = f (M, Z, Vrot)!! Yoon, Langer & Norman ( astro-ph/ )

13 Rotational velocity of metal-poor massive stars NGC 346 in SMC (age ~ a few 10 6 yrs) Data from Mokiem et al. (06)

14 GRB/SN rate according to metallicity

15 GRB/SN rate predicted from chemically homogeneous evolution Yoon, Langer & Norman (06); based on metallicity dependent star formation model by Langer & Norman (06)

16 Diversity in pre-collapsar conditions On average, higher j for lower Z.

17 First stars : metallicity = 0

18 First stars : metallicity = 0

19 Ionizing photons

20 Ionizing photons

21 Other implications of quasi-chemically homogeneous evolution WR stars at very low Z (also from pop III) Fernandes et al. 04

22 Nucleosynthesis yields? Hydrogen-free pair instability supernovae? Z=0, Minit=100 Msun Vinit/VK=0.5

23 Rapid rotators & Helium enriched NGC346

24 e.g. Fryer et al. 99 Binarity?

25 Binarity? Unevolved He star 20 Msun, Vinit = 200km/s Evolved He star

26 Conclusions/Future work Massive star evolution is not only determined by mass and metallicity but also by initial rotation velocity Chemically homogeneous evolution can lead to Gamma-ray bursts at low metallicity Pop III stars with 10 < M/Msun < 60 and Vrot/VK > ~ 0.3 can also make GRBs Observational evidence for chemically homogeneous evolution? (WR galaxies at low metallicity? NGC 356?) Binary evolution? / how can we distinguish between single-star GRB progenitors and binary ones from observations? Diversity of GRBs due to different pre-collapse conditions? Role of rotation in the first star evolution? How many GRBs? Reionization? Nucleosynthesis?