Transcript Precessing BH NS Binaries: Upper Limits on Black Hole Spins Richard O’Shaughnessy

Precessing BH NS Binaries:
Upper Limits on Black Hole Spins
Jeff Kaplan
Richard O’Shaughnessy
Vicky Kalogera
Department of Physics and Astronomy
Motivation
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Precession:
Important for BH NS
systems
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GW signal dependant on
BH spin and tilts
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Spin tilts result from
companion SN
Effect of Precession
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Spin tilts for
BH-NS systems:
Already studied
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(Apostolatos et al; Grandclement et al;
Buonanno et al)
o
Critical for > 30
Fitting Factor: Function of Tilt
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Spin Magnitudes for
BH-NS systems:
???
Rate Reduction:
Function of Magnitude
Spin Magnitudes From
Population Synthesis

StarTrack code for BH – NS formation
(Belczynski et al. 2004)
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Stable & unstable mass transfer
Stellar winds
Supernovae & natal kicks
GR & tidal evolution
Isolate populations of coalescing BH-NS
systems for wide range of StarTrack models
Examine spin evolution and mass transfer
history of BH
How do Black Holes get spun up?

Core collapse processes not well understood
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Birth spins?
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Estimate from observed NS spins
Birth NS spins: 10-20 ms.
Birth NS a: 0.019 - 0.038
Assumption: Initial BH spins negligible.
Accretion Spin up

Thin Disk
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Common Envelope (CE)
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Assume angular momentum at
innermost orbit accreted
onto BH (Bardeen 1974)
Dynamically unstable
mass transfer that leads
to spiral in and envelope
mass ejection
Results on Mass Transfer
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Thin disk Accretion
log10(Δm/m)
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F(Δm/m)
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Common Envelope Accretion
Δm/m
96%: a < 0.01
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Minimal spin-up due to thin-disk accretion
 Most of mass is accreted in CE phase!
Common Envelope Accretion
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Bad: CE accretion not well understood
Complex 3-D accretion
 Non-adiabatic hydrodynamical process
 Hypercritical accretion reaches
highly Super-Eddington rates
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Good: Assuming disk accretion – Upper Limit
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Why?
– Disks carry large angular momentum
Common Envelope Spin Up Results
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Two possibilities
BH enters CE phase:
BH
 Accretion Induced Collapse (AIC): NS
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BH
BH
Observations show NS spin up in CE inefficient
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Known Recycled Pulsar Spins that are
thought to have been spun up in CEs:
B1913+16:
 B1534+12:
 J0737-3039:
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CE
a = 0.0033
a = 0.0057
a = 0.0096
In AIC cases, expect BH birth spin to be very small
Common Envelope Spin Up Results
F(a) from Common Envelope Accretion
Probability per 0.1 spin
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BH spin - a
This is an Upper Limit! Thin disk model assumed
Precessing BH-NS and GW searches
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Astrophysical average <FF3> if
non-precessing templates are
used:
Plot Thanks to Mia Ihm
Precessing BH-NS and GW searches
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Astrophysical average <FF3> if
non-precessing templates are
used:
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Effect of Spin Magnitude
on GW signal:
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∫ f(a) • FF3(a) da = <FF3>
Plot Thanks to Mia Ihm
<FF3> = 0.84
Conclusions and Future Work
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BH-NS Binaries:
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Negligible BH accretion and spin-up in thin-disk phases
Significant BH accretion in CE phases
Upper limit on average reduction of BH-NS in-spiral
event rate: 0.84
Future Work
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Explore CE physical conditions and reduce upper limits on
BH spin-up
Better constrain BH birth spin using population models and
observed systems