progenitors of long grbs
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Matteo Cantiello Astronomical Institute Utrecht
In collaboration with
S.C.Yoon, N.Langer & M.Livio
Progenitors of long GRBs
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Outline
Collapsar scenarioRotating stellar models Single star progenitorsBinary star progenitorsObservational consequencesConclusions
Collapsar Scenario (Paczinski, Woosley)
Massive core (BH)
Rapidly rotating core (accretion disk)
Compact size
€
R* /c ≈ τ engine
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Recipe to make a long GRB
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
( Zen and The art of )
Evolving stars toward Long GRBs
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)
A possible solution: Chemically Homogeneous evolution (Yoon & Langer 2005 - Heger & Woosley 2006)
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Rotational Mixing
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Convective Core
Meridional circulation
Rotational instabilities mix rotating massive stars
Eddington-Sweet circulation most efficient process
This instability acts on tKH
€
τES ∝ τ KHωKω
⎛
⎝ ⎜
⎞
⎠ ⎟2
€
ω
Magnetic fields
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Spruit-Tyler Dynamo (Spruit 2002)
Core - Envelope coupling
1. Differential rotation winds up toroidal component of B.
2. Magnetic torques tend to restore rigid rotation
Convective Core
If the envelope slows downangular momentum is also removed from the core
Chemically Homogeneous Evolution
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
€
τ Mix
τ MS<1
The star cant build a compositional gradient and evolves quasi chemically homogeneous
Rotational mixing can efficiently mix massive stars.
If
Chemically Homogeneous Evolution II
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
TimeRSG
WR
Slow rotator
Fast rotator
Chemically Homogeneous Evolution III
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
GRB
Fast rotating massive stars can evolve q.chemically homogeneous If massloss is not too efficient (Low Z) -> Long GRB
R~1000 Rsun
RSG
R~1 Rsun
WR
Fast rotator
Slow rotator
CCSN
Chemically homogeneous evolution needs high rotational velocity (and low metallicity)
Stars born with high rotational velocity Single star progenitors (Yoon at al. 2006)
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Rotational velocity
Stars spun-up in binary systemsBinary 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)
SN
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Spin up by accretion16MSun 15MSun
LGRB
Runaway Wolf-Rayet
Rotational Mixing!!
4MSun 21MSun
M* ~ 13MSun
Mco~ 10MSun
Jco~ 2x1016cm2/s
Case B mass transfer
V ~ 30 km/s
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
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
Runaway GRBs
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
NGC 346: a cluster of young stars in the SMC
Credit: Mokiem et al. 2007
Rotational Velocity vs Surface Helium Rotational Velocity vs Radial Velocity
Low number statistics... But interesting!
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Observational consequences
Observational Consequences Position of GRB in the sky
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Hammer et. al 2006
Observational Consequences II
Darjeeling 2008 Matteo Cantiello LGRBs progenitors
Constant Density
Van Marle et al. 2006
Afterglow properties
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