Collapsar Accretion and the Gamma-Ray Burst X-Ray Light Curve Chris Lindner Milos 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 Curve Typically, long duration GRB exhibit 3 distinct phases in the first 10 3 s Phase 0 – 10 1 s – Prompt Phase Phase I – 10 2 s – Fast Decay Phase II – 10 3 s – Plateau Phase X-ray flares often occur in fast decay and plateau phase The x-ray light curve for GRB 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 Simulation 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 (> 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 (~10 2 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

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

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