White dwarf mergers,White dwarf mergers,thermonuclear supernovae,thermonuclear supernovae,and other transientsand other transients

Marten van KerkwijkMarten van KerkwijkWith Phil Chang (UWM) With Phil Chang (UWM) Stephen Justham (KIAA)Stephen Justham (KIAA)Chenchong Zhu, Chenchong Zhu, Kelly Lepo, Kelly Lepo, Wolfgang KerzendorfWolfgang Kerzendorf

Artwork from Howell 2010, Nature 463, 35

(vK et al. 2010, ApJ 722, L157;Zhu et al. arXiv:1109.4334, 2012, in prep.)

SN IaSN IaparadigmparadigmCO white dwarf accretes, either from companion, or from disk aftermerger.

As it approachesmaximum mass,C fusion is ignited.

Degenerate, hencerunaway.

CO white dwarf accretes, either from companion, or from disk aftermerger.

As it approachesmaximum mass,C fusion is ignited.

Degenerate, hencerunaway.

SN IaSN Iaparadigmparadigm

Contours calculatedusing MESA;mesa.sourceforge.net

SN IaSN IaraterateMore in spiralsthan in ellipticals

r(Ia) ~ 0.008 r(WD)

~0.0023(6) SN Iaper M⊙ formed(vs 0.22 WD/M⊙)

(Pritchet, Howell, & Sullivan2008, ApJ 683, L25;Maoz et al., 2011,MNRAS 412, 1508)

SN IaSN IaluminosityluminosityRange in duration and peak luminosity.

Most well-correlated(some sub- and super-luminous)

0.1-0.9 M⊙ 56Ni

More luminous inyounger populations

(Philips 1993, ApJ 413, L105;Hamuy et al., 1995, AJ 109, 1;Mazzali et al. 2007, Science 315, 825; Sullivan et al., 2010, MNRAS 406, 782)

Perlmutter, 2003, Physics Today 56, 53Perlmutter, 2003, Physics Today 56, 53

Trouble for MTrouble for Mchch??Too few suitable progenitorsSD: too few supersoft sources; no evidence for companion (or wind) in SN or SNR.DD: too few >Mch WD+WD, >½Mch supersoft symbiotics.

No natural reason for range in luminosity (or 56Ni mass), nor scaling with population age.

Ignition does not naturally leadto SN Ia: need deflagration turning into detonation.

SN IaSN Iapropertiesproperties~0.0023(6) SN Iaper M⊙ formed

r(Ia) ~ 0.008 r(WD)

0.1-0.9 M⊙ 56Ni

More luminous in youngerpopulations

All CO+CO?All CO+CO?SN IaSN Iapropertiesproperties~0.0023(6) SN Iaper M⊙ formed

r(Ia) ~ 0.008 r(WD)

0.1-0.9 M⊙ 56Ni

More luminous in youngerpopulations

Enough suitable progenitorsInferred from population synthesisand binary WD statistics;Note: <½Mch supersoft symbioticsare hard to detect in X rays.

Mass dependence naturally yieldsrange in luminosity (or 56Ni mass),and scaling with population age.

Ignition naturally leads to SN Ia(assuming a detonation; Shigeyama et al. 1992, ApJ 386, L13; Sim et al. 2010, ApJ 714, L52)

MergerMergerignition?ignition?Not initially: too cold, not dense enough:

0.6+0.6 M⊙ yieldsc~2.5 106 g cm-3

Tc~3 108 K(Lorén-Aguilar et al. 2007, A&A 500, 1193)

Would like c~few 107 g cm-3

Tc~6 108 K

MergerMergerignition?ignition?Later? Accretionand/or spindown can lead tocompressional heating.

Disk dense, τacc~(rdisk/h)(τdyn/α) ~2 hr! (α=0.01)

Strong B likely? B~(IΩΔΩ/R3)1/2~109..1011 GE.g., RE J0317-853: B~350 MG, P=725 s, M≃1.3 M⊙(Barstow et al., 1995, MNRAS 277, 971)

~OK: Rates, ~OK: Rates, luminosities, luminosities,

nucleosynthesisnucleosynthesis

Uncertainties:Uncertainties:

Different masses?Different masses?

Ignition due toIgnition due toaccretion/spindown?accretion/spindown?

Does runaway lead to detonation?Does runaway lead to detonation?

Do detonations, including rotation, disks, look like SN Ia?Do detonations, including rotation, disks, look like SN Ia?

MergersMergers⇒⇒ SN Ia?SN Ia?

Roughly equal and unequal mergersRoughly equal and unequal mergers

ρd/ρa>0.6 ρd/ρa<0.6

ΔM < 0.1 M⊙ ΔM > 0.1 M⊙

Hottest in centerHottest in center Hottest on interfaceHottest on interfaceMMrr(T(Tmaxmax)~M)~Maa

0.6+0.60.6+0.6 0.8+0.40.8+0.4

Explode? Flash? Burn stably?(Shen et al. 2012, ApJ 705:35)

Observational tests?Observational tests?No (leftover) companionNo (leftover) companion

No electron capturesNo electron captures⇒⇒ littlelittle 5858Ni/core radioactiveNi/core radioactive

Disk signature?Disk signature?

Observational inputObservational inputWD+WD mass distributions?WD+WD mass distributions?

WD synchronous?WD synchronous?

White Dwarf Mergers andWhite Dwarf Mergers andThermonuclear SupernovaeThermonuclear Supernovae

Early lightcurve (shocks)Early lightcurve (shocks)Search SN Ia remnantsSearch SN Ia remnants

Late lightcurve, Late lightcurve, nebular phase spectranebular phase spectra

Early lightcurve?Early lightcurve?

Phase-resolved spectraPhase-resolved spectra

VVrotrotsinsinii in short-P binaries in short-P binaries

Fractions,Fractions,OutcomesOutcomes

not notmuch? much? AIC?

sdO R CrB NS?

not He delayed det. CO ONemuch? det.? =SN Ia det.? det.?.

sdO R CrB - - - - -

Masses often dissimilar?

ELM He+

He HeCO CO ONe

Masses mostly similar?

He HeCO CO<0.7 CO>0.7 ONe+

He HeCO CO<0.7 CO>0.7 ONe

Of all “stars,” Of all “stars,” ~35% single,~50% never interact

~2% ~1% ~8% ~4%

H/He novaeCO deflag.?ONe AIC?

RamificationsRamificationsFor mergers, MFor mergers, MCHCH irrelevant – super-M irrelevant – super-Mchch SN Ia expected SN Ia expected(if they do not detonate too early; cf., Pakmor et al. 2010, Nature 463, 61)(if they do not detonate too early; cf., Pakmor et al. 2010, Nature 463, 61)

(Very?) unequal mergers may fuse C stably, leaving WD(Very?) unequal mergers may fuse C stably, leaving WD(e.g., RE J0317-853: B~350 MG, P=725 s, M(e.g., RE J0317-853: B~350 MG, P=725 s, M≃≃~1.3 M~1.3 M⊙)

ONe+ONe mergers should explode too (not AIC)ONe+ONe mergers should explode too (not AIC)

Outliers: Single degenerates reaching MOutliers: Single degenerates reaching Mchch??(pure deflagrations? SN 2002cx, 2007qd)(pure deflagrations? SN 2002cx, 2007qd)

White Dwarf Mergers andWhite Dwarf Mergers andThermonuclear SupernovaeThermonuclear Supernovae