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

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

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 Matteo Cantiello

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

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 Matteo Cantiello

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

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

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

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

Chemically Homogeneous Evolution III GRB R~1000 Rsun RSG R~1 Rsun WR Fast rotator Slow rotator CCSN 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 Matteo Cantiello

Darjeeling 2008 Matteo Cantiello LGRBs progenitors Rotational velocity Chemically homogeneous evolution needs high rotational velocity (and low metallicity) 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) Darjeeling 2008 Matteo Cantiello LGRBs progenitors Matteo Cantiello

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

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 Matteo Cantiello

Darjeeling 2008 Matteo Cantiello LGRBs progenitors 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 Matteo Cantiello

Darjeeling 2008 Matteo Cantiello LGRBs progenitors 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 Matteo Cantiello

Darjeeling 2008 Matteo Cantiello LGRBs progenitors 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 Matteo Cantiello

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 Matteo Cantiello

Observational consequences Darjeeling 2008 Matteo Cantiello LGRBs progenitors Matteo Cantiello

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

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

Darjeeling 2008 Matteo Cantiello LGRBs progenitors 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 Matteo Cantiello

Darjeeling 2008 Matteo Cantiello LGRBs progenitors Thanks! Darjeeling 2008 Matteo Cantiello LGRBs progenitors Matteo Cantiello