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Observable Signatures of the Accretion-Induced Collapse of White Dwarfs

Observable Signatures of the Accretion-Induced Collapse of White Dwarfs. Brian Metzger, UC Berkeley. w/ Tony Piro, Eliot Quataert, Niccolo Bucciantini (Berkeley) & Todd Thompson (Ohio State). OUTLINE. WD. Thermal Optical Transients (Metzger, Piro & Quataert 2008,09)

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Observable Signatures of the Accretion-Induced Collapse of White Dwarfs

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  1. Observable Signatures of the Accretion-Induced Collapse of White Dwarfs Brian Metzger, UC Berkeley w/ Tony Piro, Eliot Quataert, Niccolo Bucciantini (Berkeley) & Todd Thompson (Ohio State) OUTLINE WD Thermal Optical Transients (Metzger, Piro & Quataert 2008,09) 2) Connection to Short GRBs (Metzger, Quataert & Thompson 2008) NS

  2. Accretion-Induced Collapse (AIC) e.g. Miyaji+80, Nomoto & Kondo 91; Canal+92; Gutierrez+05 • “Failed” Thermonuclear Explosion (otherwise Type Ia SN) • Paths to AIC: T = 0.21 min • Non-Degenerate Binary Accretion:electron captures faster than nuclear burning(e.g. O-Ne WDs) 2) Double White Dwarf Merger:  Super-Chandrasekhar WD + Remnant Torus(Candidates: SPY Survey; Napiwotzki+02) Yoon+07 T = 1.7 min T = 0.86 min • AIC Rate (Very Uncertain): ~10-6-10-4 yr-1 galaxy-1

  3. Collapse to a Proto-Neutron Star • Weak Explosion ~1050 ergs, MNi < 10-3 M (Woosley & Baron 92; Fryer+99; Dessart+06) • But with Rapid Rotation…. • Gravitational Wave Source? (Fryer+02; Ott 08) 2) ~ 0.1 M, ~ 30 km Disk around NS (Michel 87; Bailyn & Grindlay 90) WD R ~ 103 km Collapse! T = 59 ms post bounce  Dessart+06 R ~ 30-100 km NS

  4. Metzger, Piro, & Quataert 2008a,b Disk Accretion and Viscous Spreading • 1D (radial) Time-Dependent Disk Evolution  Solve for Disk Spreading (alpha viscosity), Heating & Cooling  Evolve Composition (n/p) via Weak Interactions • Neutrino Cooled (Thin Disk) • Degenerate Electrons  Neutron-Rich Equilibrium Initial (t = 0) R ~ 100 km M ~ 0.1 M NS T ~ 5 MeV }

  5. Metzger, Piro, & Quataert 2008a,b Disk Accretion and Viscous Spreading • 1D (radial) Time-Dependent Disk Evolution  Solve for Disk Spreading (alpha viscosity), Heating & Cooling  Evolve Composition (n/p) via Weak Interactions • Neutrino Cooled (Thin Disk) • Degenerate Electrons  Neutron-Rich Equilibrium Initial (t = 0) R ~ 100 km M ~ 0.1 M NS T ~ 5 MeV } Final (t ~ 1 s) R ~ 1000 km • Inefficient Cooling (Thick Disk) • Degeneracy Lifted • n/p “Freezes Out” • Alpha Particles Form • Disk Blown Apart M ~ 0.03 M NS T ~ 1 MeV

  6. Disk Outflows and Nucleosynthesis }  Powerful Winds • -Particle Formation: ENuc > EBind • Thick Disks only Marginally Bound (Narayan & Yi 94; Blandford & Begelman 99) • Expansion of Hot, Dense Ejecta Heavy Element Synthesis • Critical Quantity:Neutron-Proton Ratio in Disk @ Freeze Out e.g. Se, Br, Ag e.g. Se, Br, Ag Neutron-Rich Freeze Out (with n/p ~ 2-3)  Rare Heavy Elements 1) BH Accretion(NS-NS / NS-BH Mergers) BH (Metzger, Piro, & Quataert 08a,b) e e e V ~ 0.1 c 56Ni Neutrino Irradiation 2) NS Accretion(AIC) NS  n/p ~ 1  56Ni e V ~ 0.1 c 56Ni e e

  7. Optical Transients from AIC Metzger, Piro, & Quataert 2009 • 56Ni  56Co +  heats ejecta • Photons diffuse out as ejecta expands MNi ~ 10-2 M Mtotal ~ 2 x 10-2 M 1) Optical Transient Surveys Palomar Transient Factory & PanSTARRs MDS: ~1 yr-1 (RAIC/10-2 RIa) LSST: ~ 600 yr-1 (RAIC/10-2 RIa) Ni / Fe-Rich Spectra Larger Mtotal in WD-WD Merger  Longer Duration Sub-Luminous Type Ia SNe? (e.g. 2008ha; Valenti +09; Foley+09) 2) Beacon to Gravitational Wave Source (e.g. LIGO)

  8. Circinus X-1 (ATCA 1.4 GHz) AIC as Short GRB Progenitor Tudose+06 • Relativistic Jet from NS Accretion (Analogous to BH Accretion after NS-NS / NS-BH Merger) • GRB Duration ~ Accretion Time ~ Sec • Host Galaxies: Early & Late Type Predict Location Inside galaxy or GC • No Bright Supernova (Hjorth+05) (but fainter transient lasting ~ 1 day) • Weaker / Distinct Grav. Wave Signal Heinz+07 050724; Berger+05 050709; Fox+05

  9. Short GRBs with Extended Emission GRB050709 I. II. III. Perley et al. 2008 GRB080503 SEE/SGRB ~ 30 BATSE SGRBEEs (Norris & Bonnell 2006)

  10. Extended Emission from Magnetar Spindown (Usov 92; Thompson 94; Metzger, Thompson, & Quataert 07; Metzger, Quataert, & Thompson 08)  • ERot~5 1052 erg, SD ~100 s for P ~ 1 ms& B ~ 1015 G • Emission Delay: Neutron Star Cooling Time (~10 s) NS “Proto-Magnetar” Winds (Metzger+07) Wind Evolution Internal Shock Emission 1016 G 1016 G 3 1015 G 1015 G 1016 G 3 1015 G 1015 G Metzger+08 LC ~  3 1015 G P0 = 1 ms 1015 G

  11. Summary WD NS • AIC + Rapid Rotation  Proto-Neutron Star + Accretion Disk • Disk Viscously Spreads, Neutrino Irradiation Drives n/p to ~ 1 • Thermal/Nuclear-Driven Winds blow disk apart at t ~ 1 second  ~ 10-2 M in 56Ni Synthesized in Outflow  Optical Transient with LV ~ 1041 erg s-1 for ~ 1 day (Longer Duration Possible in WD-WD Merger Case) - Detectable w/ Transient Surveys or as Beacon to G-Wave Source • NS Accretion may also Produce a Short GRB • Extended Emission from S-GRBs Hard to Explain w/ Accretion • If NS is Strongly Magnetized, EE may be Rotation Powered  Proto-Magnetar Wind + Internal Shock Emission Model Fits Data

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