Observable Signatures of the Accretion-Induced Collapse of

White Dwarfs

w/ Tony Piro, Eliot Quataert, Niccolo Bucciantini (Berkeley) & Todd Thompson (Ohio State)

Brian Metzger, UC Berkeley

WD

NS

OUTLINE

1) Thermal Optical Transients(Metzger, Piro & Quataert 2008,09)

2) Connection to Short GRBs

(Metzger, Quataert & Thompson 2008)

Accretion-Induced Collapse (AIC)

Yoon+

07

• AIC Rate (Very Uncertain):~10-6-10-4 yr-1

galaxy-1

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

T = 1.7 minT = 0.86 min

1) 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)

Collapse to a Proto-Neutron Star

Quick

Tim

e™

an

d a

TIF

F (L

ZW

) decom

pre

sso

rare

nee

de

d to

see th

is pic

ture

.

Dessart+

06

WDR ~ 103 km

Co

llapse!

NS

R ~ 30-100 km

T = 59 ms post bounce

Weak Explosion ~1050 ergs, MNi < 10-3 M (Woosley &

Baron 92; Fryer+99; Dessart+06)

But with Rapid Rotation….

1) Gravitational Wave Source? (Fryer+02; Ott 08)

2) ~ 0.1 M, ~ 30 km Disk around NS (Michel 87; Bailyn & Grindlay 90)

Disk Accretion and Viscous Spreading

NS

• Neutrino Cooled (Thin Disk)

• Degenerate Electrons

Neutron-Rich Equilibrium

€

˙ M IN

€

e− + p → ν e + n

€

e+ + n → ν e + p

R ~ 100 kmM ~ 0.1 M

T ~ 5 MeV

Initial (t = 0)

Metzger, Piro, & Quataert 2008a,b

€

n

p~ 10}

• 1D (radial) Time-Dependent Disk Evolution Solve for Disk Spreading (alpha viscosity), Heating & Cooling

Evolve Composition (n/p) via Weak Interactions

Disk Accretion and Viscous Spreading

NS

• Neutrino Cooled (Thin Disk)

• Degenerate Electrons

Neutron-Rich Equilibrium

€

˙ M INR ~ 100 km

NS

• Inefficient Cooling (Thick Disk)

• Degeneracy Lifted

• n/p “Freezes Out”

• Alpha Particles Form

• Disk Blown Apart

M ~ 0.1 MT ~ 5 MeV

Initial (t = 0)

T ~ 1 MeV

M ~ 0.03 M

R ~ 1000 kmFinal (t ~ 1 s)

Metzger, Piro, & Quataert 2008a,b

€

˙ M IN €

n

p~ 10}

• 1D (radial) Time-Dependent Disk Evolution Solve for Disk Spreading (alpha viscosity), Heating & Cooling

Evolve Composition (n/p) via Weak Interactions

€

e− + p → ν e + n

€

e+ + n → ν e + p

Disk Outflows and Nucleosynthesis -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

Powerful Winds}

BH1) BH Accretion (NS-NS / NS-BH Mergers)

2) NS Accretion (AIC)

Neutron-Rich Freeze Out (with n/p ~ 2-3) Rare Heavy Elements

NS

€

ν e + n → e− + p

n/p ~ 1

56Ni

Neutrino Irradiation

e.g. Se, Br, Ag

56Ni

e.g. Se, Br, Ag

56Ni

V ~ 0.1 c

V ~ 0.1 c νe

νe

νe νeνe

νe

(Metzger, Piro, & Quataert 08a,b)

Optical Transients from AIC• 56Ni 56Co + heats ejecta• Photons diffuse out as ejecta expands

1) Optical Transient SurveysPalomar Transient Factory & PanSTARRs MDS: ~1 yr-1 (RAIC/10-2 RIa)

LSST: ~ 600 yr-1 (RAIC/10-2 RIa)

€

Tpeak ~ 1 day M total

10−2 M8

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 2v

0.1 c

⎛

⎝ ⎜

⎞

⎠ ⎟−1/ 2

Metzger, Piro, & Quataert 2009

2) Beacon to Gravitational Wave Source (e.g. LIGO)

MNi ~ 10-2 M

Mtotal ~ 2 x 10-2 M

Ni / Fe-Rich Spectra

Larger Mtotal in WD-WD Merger Longer Duration Sub-Luminous Type Ia SNe? (e.g. 2008ha; Valenti +09; Foley+09)

AIC as Short GRB Progenitor

• 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

050724; Berger+05

050709; Fox+05

Circinus X-1 (ATCA 1.4 GHz)

Heinz+07Tudose+06

Short GRBs with Extended Emission

GRB050709

GRB080503

BATSE SGRBEEs (Norris & Bonnell 2006)

Perley et al. 2008

I.

III.II.

SEE/SGRB ~ 30

NS

ERot ~5 1052 erg, SD ~100 s for P ~ 1 ms & B ~ 1015 G

Emission Delay: Neutron Star Cooling Time (~10 s)

“Proto-Magnetar” Winds (Metzger+07)

€

B0,Ω(t), Lν (t),T0(t)⇒ ˙ M , ˙ E , ˙ J

Extended Emission from Magnetar Spindown (Usov 92; Thompson 94; Metzger, Thompson, & Quataert 07; Metzger, Quataert, & Thompson 08)

1015 G

1016 G

3 1015 G

P0 = 1 ms

1015 G

1016 G

3 1015 G

Metzg

er+08

1016 G3 1015 G

1015 G

LC

~

Wind Evolution Internal Shock Emission

Summary

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

WD NS