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The Evolution and Outflows of Hyper-Accreting Disks

The Evolution and Outflows of Hyper-Accreting Disks. Brian Metzger, UC Berkeley. with Tony Piro, Eliot Quataert & Todd Thompson. Metzger, Thompson & Quataert (2007), ApJ, 659, 561 Metzger, Quataert & Thompson (2008), MNRAS, 385, 1455 Metzger, Thompson & Quataert (2008), ApJ, 676, 1130

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The Evolution and Outflows of Hyper-Accreting Disks

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  1. The Evolution and Outflows of Hyper-Accreting Disks Brian Metzger, UC Berkeley with Tony Piro, Eliot Quataert & Todd Thompson Metzger, Thompson & Quataert (2007), ApJ, 659, 561 Metzger, Quataert & Thompson (2008), MNRAS, 385, 1455 Metzger, Thompson & Quataert (2008), ApJ, 676, 1130 Metzger, Piro & Quataert (2008a), MNRAS in press Metzger, Piro & Quataert (2008b), In preparation

  2. Outline • Introduction • Compact Object Mergers and White Dwarf AIC • Short GRBs: Recent Advances and New Puzzles • Hyper-Accreting Disk Models • One-Zone “Ring” Model • 1D Height-Integrated Model • Disk Outflows and Nucleosynthesis • Neutrino-Driven Winds (Early Times) • Viscously-Driven Winds (Late Times) • Conclusions

  3. Compact Object Mergers (NS-NS or BH-NS) Lattimer & Schramm 1974, 1976; Paczynski 1986; Eichler et al. 1989 t = 0.7 ms “Chirp” • Inspiral + NS Tidal Disruption • Primary Target for Advanced LIGO / VIRGO • Disk Forms w/ Mass ~ 10-3 - 0.3 Mand Radius ~10-100 km • Hot ( kT > MeV) and Dense ( ~ 108-1012 g cm-3) Midplane • Cooling via Neutrinos: ( >>1,  ~ 0.01-100) • Accretion Rate  GRB Progenitor? t = 3 ms Shibata & Taniguchi 2006

  4. Accretion-Induced Collapse Nomoto & Kondo 1991; Canal 1997 • Electron Capture (24Mg  20Ne  20O) Faster than Nuclear Burning  O-Ne-Mg White Dwarf Core Destabilized 776 ms post bounce Dessart+06 Md ~ 0.1 M Disk Forms Around NS

  5. Gamma-Ray Bursts: Long & Short Duration BATSE GRBs Long • High Redshift: <z> ~ 2 • Large Energies (Eiso~1052-54 ergs) • Star Forming Hosts • Type Ibc Broad-Line Supernovae Nakar 07 Short

  6. Short GRB Host Galaxies GRB050509b GRB050709 z = 0.16 SFR = 0.2 M yr-1 Bloom+ 06 z = 0.225 SFR < 0.1 M yr-1 KECK Bloom+06 HUBBLE Fox+05 GRB050724 Berger +05 z = 0.258 SFR < 0.03 M yr-1 Berger+05

  7. Short GRB Host Galaxies GRB050509b GRB050709 z = 0.16 SFR = 0.2 M yr-1 No SN! (But Some Radioactive Ejecta Expected…) Bloom +06 z = 0.225 SFR < 0.1 M yr-1 KECK Bloom+06 HUBBLE Fox+05 • Lower z • Eiso~ 1049-51 ergs • Older Progenitor Population GRB050724 Berger +05 GRB050724 z = 0.258 SFR < 0.03 M yr-1 Berger+05

  8. GRB050709 Short GRBs with Extended Emission Who Ordered That?! • Regular ~ 30-100 s Duration - Energy Often Exceeds GRB’s - ~25% of Swift Short Bursts BATSE Examples GRB050724 XRT, Campana+06 Late-Time Flaring (Norris & Bonnell 2006)

  9. A “Ring” Model of Hyper-Accreting Disks Metzger, Piro & Quataert 2008a Vr > 0 Vr < 0 rd BH • Mass at large radii ~ rd controls disk evolution and sets • Model enforces mass & angular momentum conservation • Thermal Balance: • Calculates {, T, H} @ rd(t) GIVEN rd,0, Md,0, MBH, and  Simple model allows wide exploration of parameter space: Initial disk mass/radius, viscosity , outflows, etc.

  10. 2 Three Phases of Hyper-Accreting Disks 3 1 • High Thick Disk: H ~ R - Optically Thick Matter Accretes Before Cooling • Neutrino-Cooled Thin Disk: H ~ 0.2 R • Optically Thin, Neutrino Luminosity L ~ 0.1 c2 • Ion Pressure Dominated / Mildly Degenerate • Neutron-Rich Composition (n/p ~ 10) • Low Thick Disk: H ~ R • Neutrino Cooling << Viscous Heating • Radiation Pressure-Dominated / Non-Degenerate

  11. Example Ring Model Solution MBH = 3 M Md,0 = 0.1 M rd,0 = 30 km  = 0.1 tvisc,0 ~ 3 ms M (M s-1) rd (km) . Mdt-1/3 0.1 Mdc2 (1051 ergs) T (MeV) tthick

  12. Late-Time Thick Disk Outflows Advective disks are only marginally bound. When the disk cannot cool, a powerful viscously-driven outflow blows it apart (Blandford & Begelman 1999). Only a small fraction of ingoing matter actually accretes onto black hole BH Nuclear energy from -particle formation also sufficient to unbind disk Hawley & Balbus 2002

  13. Effect of the Thick Disk Wind Late-Time Short GRB Activity • XRBs Make Radio Jets Upon Thermal (Thin Disk)  Power-Law (Thick Disk) Transition (e.g. Fender +99; Corbel + 00; Fender, Belloni, & Gallo 04; Gallo +04) • Extended Emission = Thick Disk Transition? • Problem: Requires Very Low Viscosity  ~ 10-3 tthick?

  14. Tidal Tail Fallback Other Sources of Extended Emission Rosswog 06, Lee & Ramirez-Ruiz 07 Lee & Ramirez-Ruiz 07 Magnetar Spin-Down Following AIC P0= 1 ms 1016 G GRB060614 Overlaid Metzger, Quataert & Thompson 08  3 1015 G NS High  Low  1015 G

  15. Disk Outflows & Heavy Element Synthesis • GRB Jets Require Low Density, but High Density Outflows Probably More Common  Heavy Element Formation • EBIND ~ 8 MeV nucleon-1  vOUT ~ 0.1-0.2 c • Which Heavy Isotopes are Produced Depends on: Electron Fraction Ye = np/(nn+np)

  16. (Ye = 0.88) (Ye ~ 0.5) Rare Neutron-Rich Isotopes (Ye ~ 0.3 - 0.4) 2nd/3rd Peak r-Process (Ye < 0.3) (Ye < 0.2) Atomic Number (A)

  17. Neutrino Heated Winds Original Application: Core-Collapse Supernovae (Duncan+ 84; Qian & Woosley 96; Thompson+ 01) • Neutrinos Heat & Unbind Matter from NS: • Electron Fraction at set by Neutrinos • EBIND = 150 MeV, E ~ 15 MeV  ~ 10 Neutrino Absorptions per Nucleon t = 0.5 s Burrows, Hayes, & Fryxell 1995 Emergence of the Proto-Neutron Star Wind n p n p n

  18. Neutrino-Driven Accretion Disk Winds Levinson 06; Metzger, Thompson & Quataert 08 L ~ 0.1 c2 Yedisk ~ 0.1 BH

  19. 56Ni Production in Neutrino-Driven Winds Neutron-Rich Isotopes Optically Thick @ RISCO 1 rd Optically Thin @ RISCO Metzger, Piro & Quatert 2008 Accretion Rate (M s-1) 56Ni Neutron-Rich Isotopes GMmp/2R < E GMmp/2R > E 10-1 Thin Disk Thick Disk 10-2 10 1 Wind Launching Radius (RISCO)

  20. Mini-Supernovae Following Short GRBs Li & Paczynski 1998; Kulkarni 2005; Metzger, Piro & Quataert 2008a Mini-SN Light Curve(MNi ~ 10-3 M and Mtot ~ 10-2 M) Total 56Ni Mass Integrated Over Disk Evolution: BH spin a = 0.9 GRB050509b (Hjorth +05) V J Metzger, Piro & Quataert 2008a Metzger, Piro & Quataert 2008a Optical / IR Follow-Up  Initial Disk Properties

  21. Summary So Far Neutrino-Cooled Thin Disk Phase • Neutron-Rich Midplane (Ye ~ 0.1) • Neutrino-Driven Wind  Up To ~ 10-3 M in 56Ni  Mini-SN (+ even more neutron-rich matter from larger radii) Late-Time Thick Disk Phase • Viscously-Driven Wind Disrupts Disk • Disk Composition?? Wind Composition??

  22. Late-Time Disk Composition:Disk Thickening  Weak Freeze-Out The Thick Disk Transition Degeneracy Pair Captures: Metzger, Piro & Quataert 2008b H/R Both Cool Disk AND Change Ye Yeeq Ye Weak Freeze Out  Non-Degenerate Transition  Moderately Neutron-Rich Freeze-Out (Ye ~ 0.25 - 0.45)

  23. 1D Height-Integrated Disk Calculations Md,0 = 0.1 M, rd,0 = 30 km,  = 0.3 Equations Local Disk Mass r2 (M) Angular Momentum / Continuity Entropy Heating Cooling Nuclear Composition

  24. Electron Fraction Weak Freeze-Out (A “Little Bang”) Ye Yeeq Weak Interactions Drive Ye Yeeq Until Freeze-Out Thickening / Freeze-Out Begins at the Outer Disk and Moves Inwards

  25. Neutron-Rich Freeze-Out Is Robust M0 = 0.1 M,  = 0.03 M0 = 0.1 M,  = 0.3 M per bin Mtot = 0.02 M Mtot = 0.02 M M0 = 0.01 M,  = 0.3  ~10 - 30% of Initial Disk Ejected Into ISM with Ye ~ 0.2-0.4 M per bin Mtot= 2 10-3 M

  26. Production of Rare Neutron-Rich Isotopes Hartmann +85 40 Million Times Solar Abundance!!! 0.35 < Ye < 0.4  78,80,82Se, 79Br Ye = 0.5 Ye = 0.35 Ye = 0.4 =1-2Ye

  27. Merger Rates and the Short GRB Beaming Fraction Metzger, Piro & Quataert 2008b From known merging NS systems, Kim+06 estimate: Milky Way Short GRB Rate ~ 10-6 yr-1 (Nakar 07) Jet Opening Angle  > 300 Short GRBs Less Collimated than Long GRBs (LGRB~2-100) (Grupe +06; Soderberg +06)

  28. Timeline of Compact Object Mergers • Inspiral, Tidal Disruption & Disk Formation (t ~ ms) • Optically-Thick, Geometrically-Thick Disk (t ~ ms) • Geometrically-Thin Neutrino-Cooled Disk (t ~0.1-1 s) - Up to ~ 10-3 M in56Ni from neutrino-driven winds (mini-SN) • Radiatively Inefficient Thick Disk (t > 0.1-1 s) - Degenerate  Non-Degenerate - PGAS-Dominated PRAD-Dominated - Neutron-Rich Freeze-Out Disk Blown Apart by Viscously-Driven Outflow - Creation of Rare Neutron-Rich Elements (“Little Bang”)

  29. 56Ni From AIC Disk Winds • Neutrino absorptions don’t affect Ye strongly in compact merger disks • BUT In AIC, e“flash” from shock break-out can drive Ye > 0.5 Dessart+ 06 “Flash” Neutrino Luminosity (ergs s-1) Freeze-Out Ye in AIC Disk Time After Core Bounce (s) •  Winds synthesize ~10-2 M in 56Ni • Optical Transient Surveys: ~ few yr-1 Pan-STARRs & PTF ~ 100’s yr-1 LSST • Neutron-rich material also synthesized?  unusual spectral lines? (e.g, Zn, Ge, Cu?) With e Flash No e Flash

  30. Conclusions • Isolated Disk Evolution Cannot Explain Late-Time X-Ray Emission (unless  ~ 10-3) • Promising alternatives: Tidal tail fall-back and magnetar spin-down • Neutrino-driven winds create up to ~10-3M in 56Ni • Mini-SN at t ~ 1 day • Neutron-Rich Nucleosynthesis • CO merger rate: < 10-5 yr-1(Md,0/0.1M)-1 • Short GRB jet opening angle:  > 30(Md,0/0.1M)1/2 • ~10-2 M in 56Ni from White Dwarf AIC • Target for upcoming optical transient surveys

  31. Future Progress Observations Gravitational Waves (LIGO; VIRGO) Short GRB Optical / IR Follow-Up Spectroscopy of Metal-Poor Halo Stars Optical Transient Surveys Theory MHD Disk Simulations: Freeze-Out and Late-Time Winds Compact Object Merger Simulations Spectra of Neutron-Rich Explosions Neutron-Rich Nucleosynthesis

  32. Late-Time Optical Rebrightening: Mini-Supernova? GRB060614; Mangano+07

  33. Merger Rates and the GRB Beaming Fraction For tgalaxy = 10Gyr and MISM = 109 M: • If a fraction  ~ 0.1 of initial disk mass is ejected with Ye < 0.4 per event: From known merging NS systems, Kim+06 estimate: Milky Way Short GRB Rate ~ 10-6 yr-1 (Nakar 07) Jet Opening Angle  > 100 Short GRBs Less Collimated than Long GRBs (LGRB~2-100)

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