Progenitors of long GRBs

1. Progenitors of long GRBs Matteo Cantiello Astronomical Institute Utrecht In collaboration with S.C.Yoon, N.Langer & M.Livio

2. Outline • Collapsar scenario • Rotating stellar models • Single star progenitors • Binary star progenitors • Observational consequences • Conclusions Darjeeling 2008 Matteo Cantiello LGRBs progenitors

3. Recipe to make a long GRB Collapsar Scenario(Paczinski, Woosley) • Massive core (BH) • Rapidly rotating core (accretion disk) • Compact size Darjeeling 2008 Matteo Cantiello LGRBs progenitors

4. ( Zen and The art of ) Evolving stars toward Long GRBs Darjeeling 2008 Matteo Cantiello LGRBs progenitors

5. The “angular momentum” problem • Collapsar needs compact progenitor with massive, fast rotating core • Canonical evolution of single stars including rotation and B fields cant produce such an object A possible solution: Chemically Homogeneous evolution (Yoon & Langer 2005 - Heger & Woosley 2006) Darjeeling 2008 Matteo Cantiello LGRBs progenitors

6. Meridional circulation Convective Core Rotational Mixing • Rotational instabilities mix rotating massive stars • Eddington-Sweet circulation most efficient process • This instability acts on tKH Darjeeling 2008 Matteo Cantiello LGRBs progenitors

7. Convective Core If the envelope slows down angular momentum is also removed from the core Magnetic fields • Spruit-Tyler Dynamo (Spruit 2002) • Core - Envelope coupling Differential rotation winds up toroidal component of B. Magnetic torques tend to restore rigid rotation Darjeeling 2008 Matteo Cantiello LGRBs progenitors

8. Chemically Homogeneous Evolution Rotational mixing can efficiently mix massive stars. If The star cant build a compositional gradient and evolves quasichemically homogeneous Darjeeling 2008 Matteo Cantiello LGRBs progenitors

9. Chemically Homogeneous Evolution II Slow rotator RSG Time Fast rotator WR Darjeeling 2008 Matteo Cantiello LGRBs progenitors

10. CCSN GRB WR R~1 Rsun Fast rotator R~1000 Rsun RSG Slow rotator Chemically Homogeneous Evolution III • Fast rotating massive stars can evolve q.chemically homogeneous • If massloss is not too efficient (Low Z) -> Long GRB Darjeeling 2008 Matteo Cantiello LGRBs progenitors

11. Rotational velocity Stars born with high rotational velocity Single star progenitors(Yoon at al. 2006) Stars spun-up in binary systems Binary star progenitors(Cantiello et al. 2007) • Chemically homogeneous evolution needs high rotational velocity (and low metallicity) Darjeeling 2008 Matteo Cantiello LGRBs progenitors

12. Single star progenitors (review) • Long GRBs prefer low metallicity (i.e. weaker winds) Z 0.004 (SMC) • But important role of wind massloss in determining the metallicity threshold Yoon, Langer and Norman, 2006 Darjeeling 2008 Matteo Cantiello LGRBs progenitors

13. Binary star progenitors • We want to spin-up a star and induce chemically homogeneous evolution Mass (angluar momentum) accretion Darjeeling 2008 Matteo Cantiello LGRBs progenitors

14. Spin up by accretion We used a 1D hydrodynamic binary evolution code to evolve massive binary systems (rotation and magnetic fields included). • 16+15 MSun • P= 5 days • SMC metallicity (Z=0.004) Darjeeling 2008 Matteo Cantiello LGRBs progenitors

15. Spin up by accretion 16MSun 15MSun Case B mass transfer 4MSun 21MSun M* ~ 13MSun Mco~ 10MSun Jco~ 2x1016cm2/s SN Rotational Mixing!! Runaway Wolf-Rayet V ~ 30 km/s LGRB Darjeeling 2008 Matteo Cantiello LGRBs progenitors

16. Results • This model explains how a massive star can obtain the high rotational velocity needed to evolve quasi-chemically homogeneous and fulfills the Collapsar scenario for Long GRBs • Unlike the single star model, the star doesn’t need to be born with an high rotational velocity Runaway GRBs • The donor star dies as a SN type Ib/c 7Myrs before the collapse of the accreting companion • The system is likely to be broke up by the SN kick (80%) • The accreting companion becomes a Runaway WR star and travels few hundred pc before producing a Long GRB Darjeeling 2008 Matteo Cantiello LGRBs progenitors

17. NGC 346: a cluster of young stars in the SMC Rotational Velocity vs Surface Helium Rotational Velocity vs Radial Velocity Credit: Mokiem et al. 2007 Low number statistics... But interesting! Darjeeling 2008 Matteo Cantiello LGRBs progenitors

18. Observational consequences Darjeeling 2008 Matteo Cantiello LGRBs progenitors

19. Hammer et. al 2006 Observational Consequences • Position of GRB in the sky Darjeeling 2008 Matteo Cantiello LGRBs progenitors

20. Constant Density Van Marle et al. 2006 Observational Consequences II • Afterglow properties Darjeeling 2008 Matteo Cantiello LGRBs progenitors

21. Conclusions • Fast rotating massive stars can evolve chemically homogeneous and become long GRBs • Two classes of progenitors: single and binary stars • In massive binaries it’s possible to spin up a star and obtain a collapsar • This scenario is likely to produce a runaway WR which travel several hundred pc before collapse • Observational consequences for the Runaway GRBs • Position in the sky • Afterglow (maybe) characterized by a constant density medium • Both single and binary progenitors prefer low Z Darjeeling 2008 Matteo Cantiello LGRBs progenitors

22. Thanks! Darjeeling 2008 Matteo Cantiello LGRBs progenitors