APT5 - Alternative Black Hole Models |
Speaker_ |
Kundt, Wolfgang |
Co-autors |
None |
Talk _ |
Neutron-Star Atmospheres and X-ray Spectra |
Abstract _ |
Neutron Stars are thought to be good conductors, anchoring strong, corotating magnetospheres and radiating at (patchy) surface temperatures below 10^7 K. Even if their far fields are dipolar, stability (inside a fluid star) requires a `toroidal bandage´ - most likely acquired during the progenitor star's core collapse - so that their fields can be described by odd-order multipole expansions: `dipole + octupole + + 2^5-pole + ...´. A rotating magnet generates unipolar-induction E-fields which accelerate electrons and positrons to Lorentz factors e beta B h^2/m_e c^2 R > (h/cm)^2 >> 1 for transient vacuum gaps of height h, both `upward´ and `downward´ from its surface. Most of them will escape to infinity, along the `open´ B-lines, but some minority at least will bombard the star's surface, achieving a surface tempera- ture T_s = 10^6.5 K for typical n* values and a small assumed downward power fraction (of a few %), as a balance between bombardment and blackbody radiation. At this high T_s, the pair corona has a scale height H = kT/m_e g =10^4 cm T_7, and saturates when it gets opaque to pair annihilation, at an estimated opacity of tau = sigma_T/sigma_ann of order 10 for Thompson scattering, so that it is optically thick to the star's cooling radiation (at soft X-rays), resulting in the observed blackbody spectra. |