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Accretion in Binaries II

Accretion in Binaries II. Classes of X-ray binaries Low-mass (BH and NS) High-mass (BH and NS) X-ray pulsars (NS) Be/X-ray binaries (NS) Distinguishing NS versus BH binaries. X-Ray Binaries. Low mass: companion star mass less than one solar mass

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Accretion in Binaries II

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  1. Accretion in Binaries II • Classes of X-ray binaries • Low-mass (BH and NS) • High-mass (BH and NS) • X-ray pulsars (NS) • Be/X-ray binaries (NS) • Distinguishing NS versus BH binaries

  2. X-Ray Binaries • Low mass: companion star mass less than one solar mass • High mass: companion star mass greater than one solar mass.

  3. Wind Fed Accretion r acc bow shock matter collects in wake

  4. Wind Fed Accretion Matter in wind will accrete if its speed is less than the escape speed from the compact object at the radius of closest approach Vw = wind velocity Vx = velocity of compact object Rc = capture radius

  5. Luminosity If a neutron star binary has the following parameters, Dorb=1012 cm, vw= 1000 km/s,

  6. Accreting Pulsars High mass X-ray binary

  7. Accretion in magnetic field

  8. Magnetosphere boundary Magnetopheric boundary, rM, is where the magnetic pressure balances the ram pressure of accreted matter Assuming spherical accretion and a dipole field with the dipole moment m = BSRS3, where RS and BS are the radius of the star and the field strength at the surface.

  9. Accretion Torque

  10. Accretion Torque

  11. Pulse Period Variations

  12. What happens if the spin rate of the pulsar is faster than Keplerian rotation rate at the magnetospheric boundary? Corotation radius lies outside magnetopheric boundary

  13. Equilibrium Period The accreted matter ceases to transfer angular momentum to the neutron star when For a maximum (Eddington) luminosity and typical neutron star mass and radius, we have

  14. Emission Geometry Accreted plasma Shock front Hot spot Settling matter

  15. Pulse Profiles

  16. Landau Levels Quantization of energy due to magnetic field: Landau levels where is the momentum of the electron parallel to the field, n is the quantum number, and Bcritis the critical field, For B << Bcrit, the spacing between adjacent levels is

  17. Cyclotron Lines

  18. X-Ray Pulsar Cen X-3 Pulses are modulated at orbital period of 2.09 days

  19. Distinguishing BH vs NS Mass function

  20. Compact object masses

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