1 / 19

Shock breakouts of exploding massive stars: A MHD void model

Shock breakouts of exploding massive stars: A MHD void model. Ren-Yu HU and Yu-Qing LOU. Physics Department and Tsinghua Centre for Astrophysics (THCA), Tsinghua University, China.

vladimir-dejesus
Download Presentation

Shock breakouts of exploding massive stars: A MHD void model

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Shock breakouts of exploding massive stars: A MHD void model Ren-Yu HU and Yu-Qing LOU Physics Department and Tsinghua Centre for Astrophysics (THCA), Tsinghua University, China

  2. This research has been supported in part by the NSFC grants 10373009 and 10533020 at the Tsinghua University, and by the SRFDP 20050003088 and the Yangtze Endowment from the Ministry of Education at Tsinghua University. Acknowledgments 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  3. Peaked at 63±7 s Expotential decay: 129 ± 6 s Spectral softening Fast rise The latest shock break-out event XRO 080109/SN 2008D • Swift detected prompt X-ray emission since 2008 Jan 9.5645 UT from NGC 2770 (z=0.006494). • EX=2×1046 erg, LX, p=6.1×1043 erg s-1 • The X-ray transient is followed by a supernova classified as Type Ibc. • The radius of progenitor is estimated to be ~ 1011 cm, corresponding to a Wolf-Rayet (WR) star. • Based on the optical/ultraviolet light curve, EK ~ 2-4×1051 erg, Mej ~ 3-5 M ⊙. Soderberg et al., 2008, Nature,453, 469 How to interpret physically the X-ray light curve? What determines the fast rise time and the decay time? 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  4. A magnetofluid under self-gravity in quasi-spherical symmetry A MHD Model Mass conservation Momentum conservation 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  5. Self-similar transformation A MHD Model Magnetic induction eq. Equation of state: general polytropic k: sound parameter ; n: scaling index parameter 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  6. Several integrals Nonlinear ODEs A MHD Model nx-v=0 -> m=0 : a central cavity h: magnetic parameter q: self-similar parameter q=2(γ+n-2)/(3n-2) : singular surface 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  7. MHD shock jump conditions A MHD Model • We consider different sound speed (temperature) across a shock front. • Entropy increases from upstream to downstream sides. 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  8. n=0.85, q=0, γ =1.15, h=0 Density approaches to a finite value on the void boundary. Various upstream dynamical behaviours, depend on α*, and the dimensionless shock position. Global void solutions Lou & Hu, 2008, in preparation 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  9. An expanding central void (cavity, bubble) • Bondi-Parker radius • The central remnant compact object (or fireball; fireshell) : ~ 1 M⊙ • The sound speed at the inner edge of stellar envelope: ~ 3×109 cm s-1 • rBP ~ 4×106 cm • rvoid > 108 cm within 1s after the core collapse A MHD Model Janka & Müller 1996, A&A, 306, 167 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  10. Evolution of a shock • Rshock∝tn • * : Simulation of an exploding massive star (15 M⊙) by Janka & Müller (1996, A&A, 306, 167) • Solid line: our model with n=1.57, =0.43, q=0, h=0, dimensionless downstream shock point xsd=7.36 • Conclusion: the shock evolves in a self-similar manner. • <1: significant energy input • n>1: shock expands faster and fastter Lou & Hu, 2008, in preparation 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  11. Modeling a shock break-out • Radial profiles of an exploding WR star: • Self-similar parameters: n=0.8, =1.2, q=0, h=0, α* =0.3, x*=0.5, xsd=3.2 • Enclosed mass at r=1011 cm: 3.8 M⊙ • Kinetic energy ~ 3×1051 erg > the gravitational energy ~ 1050 erg. • The X-ray radiation of an exploding star: • Plasma cooling rate L  f(T)n2 (Sutherland & Dopita, 1993, ApJS, 88, 253) • The stellar envelope is optically thick  only the surface layer produces observable radiation. 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  12. Modeling a shock break-out • Radial profiles of an exploding WR star: • Self-similar parameters: n=0.8, =1.2, q=0, h=0, α* =0.3, x*=0.5, xsd=3.2 • Enclosed mass at r=1011 cm: 3.8 M⊙ • Kinetic energy ~ 3×1051 erg > the gravitational energy ~ 1050 erg. • The X-ray radiation of an exploding star: • Plasma cooling rate L  f(T)n2 (Sutherland & Dopita, 1993, ApJS, 88, 253) • The stellar envelope is optically thick  only the surface layer produces observable radiation. 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  13. Modeling a shock break-out • Radial profiles of an exploding WR star: • Self-similar parameters: n=0.8, =1.2, q=0, h=0, α* =0.3, x*=0.5, xsd=3.2 • Enclosed mass at r=1011 cm: 3.8 M⊙ • Kinetic energy ~ 3×1051 erg > the gravitational energy ~ 1050 erg. • The X-ray radiation of an exploding star: • Plasma cooling rate L  f(T)n2 (Sutherland & Dopita, 1993, ApJS, 88, 253) • The stellar envelope is optically thick  only the surface layer produces observable radiation. 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  14. Modeling a shock break-out t=490 s • Radial profiles of an exploding WR star: • The self-similar parameters: n=0.8, =1.2, q=0, h=0, α* =0.3, x*=0.5, xsd=3.2 • The enclosed mass at r=1011 cm: 3.8 M⊙ • The kinetic energy ~ 3×1051 erg > the gravitational energy ~ 1050 erg. • The X-ray radiation of an exploding star: • Plasma cooling rate L  f(T)n2 (Sutherland & Dopita, 1993, ApJS, 88, 253) • The stellar envelope is optically thick  only the surface layer produces observable radiation. 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  15. Modeling a shock break-out t=552 s • Radial profiles of an exploding WR star: • Self-similar parameters: n=0.8, =1.2, q=0, h=0, α* =0.3, x*=0.5, xsd=3.2 • Enclosed mass at r=1011 cm: 3.8 M⊙ • Kinetic energy ~ 3×1051 erg > the gravitational energy ~ 1050 erg. • The X-ray radiation of an exploding star: • Plasma cooling rate L  f(T)n2 (Sutherland & Dopita, 1993, ApJS, 88, 253) • The stellar envelope is optically thick  only the surface layer produces observable radiation. 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  16. Modeling a shock break-out t=680 s • Radial profiles of an exploding WR star: • Self-similar parameters: n=0.8, =1.2, q=0, h=0, α* =0.3, x*=0.5, xsd=3.2 • Enclosed mass at r=1011 cm: 3.8 M⊙ • Kinetic energy ~ 3×1051 erg > the gravitational energy ~ 1050 erg. • The X-ray radiation of an exploding star: • Plasma cooling rate L  f(T)n2 (Sutherland & Dopita, 1993, ApJS, 88, 253) • The stellar envelope is optically thick  only the surface layer produces observable radiation. 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  17. Modeling a shock break-out • We reproduce the observed X-ray light curve. • A surface layer thickness: 9×109 cm. • The X-ray decay actually follows a power law, with the starting time to be the moment of core collapse. • With larger thickness of the surface layer, both the rise and decay will be slower. • But the ratio between the characteristic rise and decay times is independent of the thickness (or optical depth). • The effective temperature of the surface layer decreases  the spectral softening [s] 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  18. Equivalent e-folding 128 s F  t-4.3 Fast rise in 62 s Shock reaches the surface layer Shock breaks out Modeling a shock break-out • We reproduce the observed X-ray light curve. • A surface layer thickness: 9×109 cm. • The X-ray decay actually follows a power law, with the starting time to be the moment of core collapse. • With larger thickness of the surface layer, both the rise and decay will be slower. • But the ratio between the characteristic rise and decay times is independent of the thickness (or optical depth). • The effective temperature of the surface layer decreases  the spectral softening [s] 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

  19. We show a semi-analytical self-similar MHD void model in quasi-spherical symmetry for a stellar explosion scenario. A shock travels outwards in a self-similar manner. We offer a dynamic void model of the progenitor of XRO 080109/SN 2008D. The shock breaks out from the photosphere ~ 552 s after the core collapse. We reproduce the observed X-ray light curve. We interpret the fast rise as the shock traveling into the surface layer, and the decay as the power law revealing a self-similar evolution. The fast rise time gives an independent measure of the thickness of the surface layer, then of the optical depth. Conclusions 2008 Nanjing GRB Conference Hu Ren-Yu Tsinghua University

More Related