Download Binary star progenitors of long GRBs

Progenitors of long GRBs
Matteo Cantiello
Astronomical Institute Utrecht
In collaboration with
S.C.Yoon, N.Langer & M.Livio
Outline
 Collapsar scenario
 Rotating stellar models
 Single star progenitors
 Binary star progenitors
 Observational consequences
 Conclusions
Darjeeling 2008
Matteo Cantiello
LGRBs progenitors
Recipe to make a long GRB
Collapsar Scenario (Paczinski, Woosley)
 Massive core
(BH)
 Rapidly rotating core
(accretion disk)
 Compact size
R* /c   engine
Darjeeling 2008
Matteo Cantiello
LGRBs progenitors
( Zen and The art of )
Evolving stars toward Long GRBs
Darjeeling 2008
Matteo Cantiello
LGRBs progenitors
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
Rotational Mixing
 Rotational instabilities mix rotating massive stars
 Eddington-Sweet circulation most efficient process

 This instability acts on tKH
Meridional
circulation
 K 
 ES   KH  
  
2
Darjeeling 2008

Matteo Cantiello
Convective
Core
LGRBs progenitors
Magnetic fields
 Spruit-Tyler Dynamo (Spruit 2002)
 Core - Envelope coupling
1. Differential rotation winds up
toroidal component of B.
Convective
Core
2. 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
Chemically Homogeneous Evolution
Rotational mixing can efficiently mix massive stars.
If
 Mix
1
 MS
The star cant build a compositional gradient and
evolves quasi chemically homogeneous

Darjeeling 2008
Matteo Cantiello
LGRBs progenitors
Chemically Homogeneous Evolution II
Slow rotator
RSG
Time
Fast rotator
WR
Darjeeling 2008
Matteo Cantiello
LGRBs progenitors
Chemically Homogeneous Evolution III
RSG
GRB
WR
R~1 Rsun
R~1000 Rsun
CCSN
Fast rotator
Slow rotator
 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
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
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
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
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
Spin up by accretion
16MSun
SN
15MSun
Case B mass transfer
Rotational
Mixing!!
Runaway
Wolf-Rayet
4MSun
21MSun
M* ~ 13MSun
Mco~ 10MSun
Jco~ 2x1016cm2/s
V ~ 30 km/s
LGRB
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
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
Observational consequences
Darjeeling 2008
Matteo Cantiello
LGRBs progenitors
Observational Consequences
 Position of GRB in the sky
Hammer et. al 2006
Darjeeling 2008
Matteo Cantiello
LGRBs progenitors
Observational Consequences II
 Afterglow properties
Constant Density
Van Marle et al. 2006
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
Thanks!
Darjeeling 2008
Matteo Cantiello
LGRBs progenitors