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Simon Johnston- how to radio pulsars spin down (P-pdot plot (Consider…
Simon Johnston- how to radio pulsars spin down
General pulsar stuff
Evolution
Massive star
Supernova
neutron star
Fast spin
Pulsar
Like space clocks
Properties
1.4 Msun
15km
P=0.001-23s
Huge flywheel, hard to stop
Appearance
Pre-discovery
Oblique rotator
High b fields
high compression
Energy loss spin down
Magnetic field decay
alignment
Crab nebula should have one
Post-discovery
Open field lines
Em radiation escapes to distant observer
lighthouse model
Papers
Chadwick 1932 discovery of neutron
Baade Zwicky 1934
Pacini 1967
Gold 1968
Textbooks
Handbook of pulsar astronomy
pulsar astronomy
Observations
RA, dec
period P
Spin down rate
dispersion measure (DM, distance proxy)
Maths
slide 11-12
21
P-pdot plot
Evolutionary tool
lots of different diagrams
Information on magnetic field, spin down energy and age
Limitations
Geometry neglected moment of inertia constant
So not direct measurement
How does pulsar move in p-pdot space
Consider
Energy loss
be field amplification/decay
changing geometry
interior/exterior coupling
Magnetosphere and plasma
ellipticity changes
Asteroids, external influencs
Precession
Consideration manifestations
Timing noise
Torque changes and higher order rotational derivatives (braking index)
Glitches
Correlation between profile changes and spin down
quasi periodic modulations
Why care
Neutron star interior physics
gravitational wave detection
plasma physics
population analysis
Long term evolution
Movement on P-Pdot diagram
need to observe for a million years
Short term evolution
Timing noise
glitches
magnetosphere switching or other effects
Where are they born in p-pdot space possibilities
Diagram
Crab like, 20ms, high B
Magnetars
1509 like, p=150ms lower B
Milli-second pulsars (MSPs) born in situ
How do they move
Pulsars born fast (Crab-like)
No magnetic field decay
constant braking index
How do they really move
Pulsars born fast
No magnetic field decay
alignment between magnetc and rotation axes wit time
timing noise term
variable braking index
Critical point- magnetic field is not changing in spite of what P-Pdot values might tell you
Misc
In past looked for where millisecond pulsars came from
To do with binary systems
Evidence for alignment
Interpulse population as a function of pulse period and concluded that alignment must occur because of the lack of interpulse pulsars at long periods
Widths of radio pulsars and concluded they were not consistent with a random alpha distribution
Are high B-field pulsars different
For both B decay and alpha decay tracks become vertical in the P-Pdot diagram
Glitches
Sudden discontinueties in the spin of a pulsar (starquakes)
Relationship with timing noise
hundreds of glitches now known and kept in JBCA glitch database
glitch sizes bi-modal, big and small but the small end suffers from selection effects
Timing noise
Timing noise is a "red" process, the fourier transform of the time series is a very steep power law
Relationship with glitches?
Strong scaling with spin frequency
MSPs have timing noise 10e4 weaker than normal pulsars, but still large enough to be dangerous for GW detection
Magnetars have the highest levels of timing noise
Timing noise caused by shear-driven turbulence in the superfluid. Predicts red noise spectrum and matches reasonably well with observations
scatter in the plot reflects the different nuclear conditions in different stars masss, density, temperature)
Braking Index
glitches strongly influence the spin-down of pulsars
Magnetosphere
Conditions effect the spin-down
Mostly in intermittent pulsars but also in pulsars more generally
asteroid impacts?
planets?
quasi-periodic modulations in the iming noise for 8 pulsars
debris disks?
free precession?