neutron star kicks
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Neutron Star Kicks. Chris Fryer Aimee Hungerford Frank Timmes. Observational Evidence and constraints on kicks Theoretical kick mechanisms. NS Kicks required for some binary systems. Be-X-ray Binaries (van den Heuvel & Rappaport 1987; Martin et al. 2009) - PowerPoint PPT PresentationTRANSCRIPT
Neutron Star KicksChris FryerAimee HungerfordFrank Timmes
Observational Evidence and constraints on kicks Theoretical kick mechanisms
NS Kicks required for some binary systems
• Be-X-ray Binaries (van den Heuvel & Rappaport 1987; Martin et al. 2009)
• Misalignment of PSR J0045-7319 (Kaspi et al. 1996)
• DNS progenitor orbital separations require kicks (Fryer & Kalogera 1997)
• BH systems also have kicks (Fragos et al. 2009)
• Clusters argue for low kicks as well (Fryer et al. 1998; Pfahl et al. 2002)
Large Kicks and Possible Bimodality from Pulsar Velocities
• With new, larger, distances, Lyne and Lorimer (1994) argued for mean velocities of roughly ~450km/s.
• Arzoumanian et al. (2002) confirm the high velocities and confirmed the better fit of a bimodal distribution suggested by binary and cluser issues.
• Fauchier-Giguere & Kaspi (2006) found a single Maxwellian + tail fit to the data
• But see Hobbs et al. (2005)
Alignment of Kick and Explosion Asymmetry
• Some kicks appear to be aligned with the asymmetries in the ejecta, others do not.
• The magnitude of the kick doesn’t seem to correlate with magnetic field strength.
Alignment of Kick and Spin
• There appears to be a bimodal alignment of kick and spin (the kick is parallel and perpendicular to the spin axis). More than one kick mechanism (Johnston et al. 2005, Ng & Romani 2007, Rankin 2007, Kuranov et al. 2009).
• Willems et al. (2004) place further constraints on kick/spin alignment from DNS systems.
NS Kicks: Observational Summary
• Large velocities observed in the pulsar population implying large kicks at/near birth.
• Pulsar + binary data suggests bimodal distribution likely
• Some kicks along ejecta asymmetry axis, some not
• Some kicks along spin axis, some not (bimodal?)• No obvious correlation between dipole magnetic
field strength and kick velocity.
NS Kick Mechanisms
• Pulsar Rocket – a post-formation kick model.• Asymmetric Collapse• Convective asymmetries – rotation• Convective asymmetries – e.g. standing accretion shock instability• Asymmetric neutrinos – sterile neutrinos in core• Asymmetric neutrinos – neutrino emission at neutrinosphere
Neutrino-Driven Supernova Mechanism
Temperature and Density of the Core Becomes so High that: Iron dissociates into alpha particles Electrons capture onto protonsCore collapses nearly at freefall!
Core reaches nuclear densities Nuclear forces and neutron degeneracy increase pressure
Bounce!
Radius (km)
Vel
ocit
y (c
)
Vel
ocit
y (c
)
Radius (km)
Neutrino-Driven Supernova Mechanism: Convection
Fryer 1999
Upflow
Downflow
Proto-NeutronStar
AnatomyOf the ConvectionRegion
Fryer & Warren 2002
AccretionShock
The convective engine also explains why, even though the collapse releases 1053 ergs of energy, the observed explosion is only a few times 1051 ergs. SASI instabilities occur later, and hence will produce weaker explosions and more massive remnants.
NS Kick Mechanisms – Pulsar Rocket
• Harrison and Tademaru (1975) argued that asymmetric pulsar emission would then produce a net motion along a pulsars spin axis.• Advantages: steady acceleration (may explain runaway OB stars)• Disadvantages: requires long-lived quadrupole moments or some such asymmetry.
Summary of KicksAsym. Collapse
Rotating SN
SASI Sterile Neutrino
Neutrino-sphere
Dipole B Depend.
Yes?
Kick along ejecta Asym
?
Kick along spin axis
Yes
Bimodal Kick
B field
One mechanism does not explain all the data!
Asymmetries in the Collapse may cause kicks
Large-scale mixing in the Oxygen/Silicon burning can cause asymmetries that can be magnified in the collapse and cause
kicks.
Meakin & Arnett 2007Fryer 2004
KickAsym. Collapse
Rotating SN
SASI Sterile Neutrino
Neutrino-sphere
Dipole B Depend.
Yes? No
Kick along ejecta Asym
? Yes
Kick along spin axis
Yes Not Nec.
Bimodal Kick
B field Low Mass Stars
AsymmetriesIn convectionAnd neutrino HeatingCause AsymmetriesIn theSupernovaExplosion!
ExplosionVelocitiesCan be Twice as Strong alongThe rotationEquator thanAlong the Pole!
Asym
metries from
Rotation
KickAsym. Collapse
Rotating SN
SASI Sterile Neutrino
Neutrino-sphere
Dipole B Depend.
Yes? No No
Kick along ejecta Asym
? Yes Yes
Kick along spin axis
Yes Not Nec. Yes
Bimodal Kick
B field Low Mass Stars
High spin only
Asymmetries from Single-Lobe Convection
• Convection Drives explosion.• The convective cells merge with time.• With sufficient time, Low-Mode convection develops.
Scheck et al. 2003
• Neutron Star Kicks for Slow Explosions
In 3-dimensions, the asymmetry is not quite as big.
These instabilities are evident in 3-dimensions, but the kick and the explosion asymmetry is not so dramatic (Fryer & Young 2007).
Convective instabilities: Spin and kick are not aligned
Fryer & Young 2007
KickAsym. Collapse
Rotating SN
SASI Sterile Neutrino
Neutrino-sphere
Dipole B Depend.
Yes No No No
Kick along ejecta Asym
? Yes Yes Yes – Opposite Direction
Kick along spin axis
Yes Not Nec. Yes Not Nec.
Bimodal Kick
B field Low Mass Stars
High spin only
Massive Stars
Asymmetries from Anisotropic Neutrino Emission
Fuller et al. 2003 Fryer & Kusenko 2006
Neutrino oscillation to sterile neutrinos in a
highly magnetized core can produce kicks.
KickAsym. Collapse
Rotating SN
SASI Sterile Neutrino
Neutrino-sphere
Dipole B Depend.
Yes No No No No?
Kick along ejecta Asym
? Yes Yes Yes – Opposite Direction
Yes – Same Direction
Kick along spin axis
Yes Not Nec. Yes Not Nec. Not Nec.
Bimodal Kick
B field Low Mass Stars
High spin only
Massive Stars
B field
Magnetic fields near the neutrinosphere can also produce asymmetric neutrino emission, producing neutron star kicks (not necessarily aligned with the explosion ejecta). Socrates et al. (2005)
KickAsym. Collapse
Rotating SN
SASI Sterile Neutrino
Neutrino-sphere
Dipole B Depend.
Yes? No No No No? No?
Kick along ejecta Asym
? Yes Yes Yes – Opposite Direction
Yes – Same Direction
Not Nec.
Kick along spin axis
Yes Not Nec. Yes Not Nec., but likely in fast spinning models
Yes? Yes?
Bimodal Kick
B field Low Mass Stars
High spin only
Massive Stars
B field? B field?