Program
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Atomic Transition Lines During Type I X-Ray Bursts
Philip Chang
University of California Santa Barbara
Abstract:
The discovery of the first atomic transition lines from a bursting
neutron star (NS) by Cottam, Paerels and Mendez is the solid
measurement of gravitational redshift from a NS surface. I will
review the observation and discuss the basic physics of the neutron
star atmosphere and line formation in this context. I will highlight
the important effects of Stark broadening, resonant scattering and
NLTE effects (level population) on the formation of the Fe H\alpha
and Ly\alpha lines. With the inclusion of these effects, I
reproduce the appropriate equivalent width of the observed line with
Fe columns that are consistent with solar metallicity accretion. I
also compare the fully relativisitic rotationally broadened line
profile to the data and find that the NS spin is \nu_{\rm s}\sin i
(R/10\,{\rm km}) = 32-28+52\,{\rm Hz} with 95% confidence, in
agreement with the 44.7 Hz spin detected by Villarreal and Strohmayer.
However, fine structure splitting of the line precludes a meaningful
constraint on the radius of this NS. Finally I highlight future
prospects for detecting other features on more rapidly rotationing NSs
and their application in determining both the redshift and radius to
contraint the nuclear equation of state.
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