1. Basic Properties By Dr. Lohse, University of Berlin
Pulsars
Basic Properties
By Dr. Lohse, University of Berlin

2. Supernova Explosion => Neutron Stars
(surface field)
part of angular
momentum carried
away by shell
field lines frozen
into solar plasma

3. Pulsar Statistics => 2 basic groups
number
”Normal“ Pulsars
T > 20 ms
Millisecond Pulsars
1 ms < T < 20 ms
log( T / s )
Crab: T = 33 ms Vela: T = 89 ms

4. centrifugal forces would disrupt neutron star if rotating faster!
Why T > 1 ms ?
virial theorem
centrifugal forces would disrupt neutron star if rotating faster!

5. Pulsars as Magnetic Dipole Antennas
misaligned magnetic rotator model
magnetic braking by emission of polarized magnetic dipole radiation:

6. not bad...but other braking mechanisms seem to be active in addition!
The Braking Index
magnetic braking predicts:
braking index n measurable via:
Crab: n = ± 0.005
PSR : n = 2.8 ± 0.2
PSR : n = 2.01 ± 0.02
not bad...but other braking mechanisms seem to be active in addition!

7. Magnetic Field at Surface
Crab Pulsar:

8. The Age of a Pulsar · log10 T decay of BS with τ = 107 yr T (s) 108 T

9. Example: Crab Pulsar Not too bad !! explosion observed in 1054 =>
pulsar properties today: T = 33 ms
prediction:
Not too bad !!

10. Rotating Pulsar = Unipolar Inductor
Eind surface forces 1012 times stronger than gravity (Crab)
charge particles (electrons...) dragged off surface and accelerated to large energies => • pulsar wind (power source for plerions) • coherent radio emission from e+e–-cascades in B-field at poles

11. Limit for Coherent Radio Emission
(M.A. Ruderman, P.G.Sutherland: Astrophys. J. 196 (1975) 51.)
theory for coherent emission from e+e– cascades along pole field lines =>
T (s)
log10 T
e+e– death line

12. The Pulsar Magnetosphere
magnetosphere: plasma moves along rigid field lines
Crab in X rays

13. The Pulsar Magnetosphere
rigid body approximation breaks down at
light cylinder:

14. Magnetosphere Charge Density
(P. Goldreich, W.H.Julian: Astrophys. J. 157 (1969) 839.)
ignore currents

15. Magnetosphere Charge Density
general case

16. The Origin of X and γ Radiation
vacuum gap acceleration of e± at
polar cap ??
outer gap ??
other models (J.Kirk et al.) ??
differentiate by observation
X/γ vs. radio pulse pattern
shape of high energy cut-off

17. Pulse Patterns up to Egret Energies

18. What are Millisecond Pulsars?
T (s)
log10 T
mostly binary systems!
very bright X-ray sources close to Eddington luminosity •
=> accretion!!

19. Accretion in Strong B-Fields
giant star feeds accretion disk around neutron star
accretion disk dynamics: orbits with slowly decreasing Kepler radii until plasma magnetically dominated:
Alvén radius: rM

20. Spin-Up Phase
angular momentum transfer from disk onto pulsar (friction at rM ):
log ( T (L/1030W)6/7 )
log ( -T / T )
end of spin-up at Ω = ΩKepler(rM): •
M = M
R = 10 km
L = LE

21. Spin-Up Limit spin-down due to magnetic dipole radiation T (s) log10 T
limited by spin-up (Tmin):
spin-up limit
fulfilled for all ms-binaries but not at all for normal pulsars (as expected)!!