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

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

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

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

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 Heger & Woosley 2006)
Darjeeling Matteo Cantiello LGRBs progenitors
Matteo Cantiello

6. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

7. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

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

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

10. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

11. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

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

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

14. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

15. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

16. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

18. Observational consequences
Darjeeling Matteo Cantiello LGRBs progenitors
Matteo Cantiello

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

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

21. 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 Matteo Cantiello LGRBs progenitors
Matteo Cantiello

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