Other
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...188.8402l&link_type=abstract
American Astronomical Society, 188th AAS Meeting, #84.02; Bulletin of the American Astronomical Society, Vol. 28, p.960
Other
4
Scientific paper
We investigate the mass accretion rate per unit area dot σ and magnetic field strength B for which nuclear burning in the envelope of an accreting neutron star is unstable. When B=0, high dot σ leads to very high temperatures T in the neutron star envelope, due to compressional heating. This stabilizes the nuclear burning. When Bnot =0, the electron scattering cross section becomes sigma_ {e gamma } ~ (omega /omega_c )(2) sigma_T ~ 10(-2) sigma_T for all photons traveling along the magnetic field and for photons in the extraordinary mode traveling at large angles to the field with energies hbar omega << hbar omega_C . Thus a very strong magnetic field can dramatically reduce the electron scattering cross section, which is the dominant radiative opacity in the envelope, for radiation escaping outward from the accreted matter. For B < 3 x 10(12) G, the peak of the blackbody photon number spectrum for T ~ 1 x 10(8) K (a temperature typical of the neutron star envelope) lies at an energy hbar omega > hbar omega_C , and the surface magnetic field has little effect on the radiative opacity. Under these conditions, compressional heating again produces very high temperatures in the neutron star envelope, which stabilizes the nuclear burning. Consequently, we do not expect most accretion-powered pulsars to produce Type I X-ray bursts. In contrast, for B >> 3 x 10(12) G, the peak of the blackbody photon number spectrum for T ~ 1 x 10(8) K lies at an energy hbar omega << hbar omega_C for which the electron scattering opacity is dramatically reduced. The enhanced radiative energy transport prevents the neutron star envelope from reaching the very high T otherwise expected for high dot σ. Analytic calculations indicate that under these conditions hydrogen and helium burning can be highly unstable, and consequently that strongly magnetic accreting neutron stars can produce Type I X-ray bursts. MCM acknowledges the support of a Compton Fellowship.
Lamb Don Q.
Miller Michael Coleman
Taam Ronald E.
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