Collapsar Accretion and the Gamma-Ray Burst X-Ray Light

Curve

Chris LindnerMilos Milosavljevic, Sean M. Couch,

Pawan Kumar

Gamma Ray Bursts

• High Energy (foe)• Highly Variable• Two Types– Short Duration –

Associated with compact object mergers

– Long Duration – Associated with Core-Collapse supernova

• Observable in multiple wavelengths

X-ray Light CurveTypically, long duration

GRB exhibit 3 distinct phases in the first 103 s

• Phase 0 – 101 s – Prompt Phase

• Phase I – 102 s – Fast Decay

• Phase II – 103 s – Plateau Phase

X-ray flares often occur in fast decay and plateau phase

The x-ray light curve for GRB 050315 from Vaughan et al. 2006

The Collapsar model• Outer H layers stripped

away off of a massive Wolf-Rayet progenitor

• Center of star collapses into a neutron star or black hole

• Rotation causes a disk (torus) to form

• Magnetic (?) Jets form and are able to push through the star

• Luminosity is modulated by central object accretion rate

http://www.tls-tautenburg.de/research/klose/GRB.review.htmlSimulation from MacFadyen

The Collapsar model:Questions

• Does the accretion history in the collapsar model actually mimic the variability in the X-ray light curve?

• If so, what causes the joined, distinct phases?• Is there enough material to account for late time

(> 103 -104 s) activity?

• What is the source of viscosity in the accretion disk? MRI?• Will jets actually form? Why?• What causes X-ray flares?• What is the mechanism of explosion? Jets? Neutrinos? Both?

Kumar, Narayan, & Johnson 2008

• Constructed an analytical model of collapsar accretion

• Use 14 solar mass progenitor star from Woosley & Heger 2006

• Use a basic power law model for rotation profile

• Used α-model viscosity (α=.1)

• Compute onset of accretion shock (~102 s), a steep decline phase, and plateau phase

Lindner, Milosavljevic, Couch, Kumar 2009

(Submitted to ApJ)

• 2D Hydrodynamic (HD) simulation of collapsar model using FLASH AMR HD code

• Start with same 14 Solar Mass Heger & Woosley model (16TI) WR – high rotation – low metalicity

• Use an explicit shear viscosity (modified α model)• Set up a modified outflow inner boundary at

(Rmin=5.0E7 to 2E8 cm)• Ran simulations for up to 1000 s

Lindner, Milosavljevic, Couch, Kumar 2009

(Submitted to ApJ)

• 2D Hydrodynamic (HD) simulation of collapsar model using FLASH AMR HD code

• Start with same 14 Solar Mass Heger & Woosley model (16TI) WR – high rotation – low metalicity

• Use an explicit shear viscosity (modified α model)• Set up a modified outflow inner boundary at

(Rmin=5.0E7 to 2E8 cm)• Ran simulations for up to 1000 s

Results:

(play movies)

Results: Mass Accretion

Phase 0: Quasiradial accretion

Phase I: Funnel and Thick Disk Accretion

Phase II: Funnel Outflow, Thick Disk Accretion

Phase II: Funnel Outflow, Thick Disk Accretion

Future Work

• 2D MHD Simulations• 3D Simulations – X-ray Flares?• Jets and Neutrinos• Early Universe Progenitors

Conclusions• The three initial phases of the GRB X-ray light

curve fit well with the three phases of accretion history in the collapsar model– Phase 0: Quasiradial Accretion– Phase I: Funnel and Thick Disk Accretion– Phase II: Funnel Outflow, Thick Disk Accretion

Future Work• 2D MHD Simulations• 3D Simulations – X-ray Flares?• Jets and Neutrinos• Early Universe Progenitors

• Pressure

• Pressure• Gravity

• Pressure• Gravity

• Magnetic Fields

• Pressure• Gravity

• Magnetic Fields• Radiation

Basic Equations of Hydrodynamics

Momentum Continuity:

Conservation of Energy:

Continuity of Mass:

Poisson Equation:

-Each grid point contains a full set of fluid variables

-Hydrodynamic equations allow grid coordinates to ‘talk’ to each other