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

1. Collapsar Accretion and the Gamma-Ray Burst X-Ray LightCurve Chris Lindner MilosMilosavljevic, Sean M. Couch, Pawan Kumar

2. 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

3. X-ray Light Curve Typically, 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

4. The Collapsar model • Outer H layers stripped away off of a massive Wolf-Rayetprogenitor • 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.html Simulation from MacFadyen

5. The Collapsar model:Questions • Does the accretion history in the collapsarmodel 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?

6. 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

7. 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

8. 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

9. Results: (play movies)

10. Results: Mass Accretion

11. Phase 0: Quasiradialaccretion

12. Phase I: Funnel and Thick Disk Accretion

13. Phase II: Funnel Outflow, Thick Disk Accretion

14. Phase II: Funnel Outflow, Thick Disk Accretion

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

16. 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

18. Pressure

19. Pressure • Gravity

20. Pressure • Gravity • Magnetic Fields

21. Pressure • Gravity • Magnetic Fields • Radiation

24. Basic Equations of Hydrodynamics Continuity of Mass: Momentum Continuity: Conservation of Energy: Poisson Equation:

25. -Each grid point contains a full set of fluid variables -Hydrodynamic equations allow grid coordinates to ‘talk’ to each other