Bibcode
Sanna, Andrea; Hiemstra, Beike; Méndez, Mariano; Altamirano, Diego; Belloni, Tomaso; Linares, M.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 432, Issue 2, p.1144-1161
Fecha de publicación:
6
2013
Número de citas
39
Número de citas referidas
35
Descripción
We analysed the X-ray spectra of six observations, simultaneously taken
with XMM-Newton and Rossi X-ray Timing Explorer (RXTE), of the
neutron-star low-mass X-ray binary 4U 1636-53. The observations cover
several states of the source, and therefore a large range of inferred
mass accretion rate. These six observations show a broad emission line
in the spectrum at around 6.5 keV, likely due to iron. We fitted this
line with a set of phenomenological models of a relativistically
broadened line, plus a model that accounts for relativistically smeared
and ionized reflection from the accretion disc. The latter model
includes the incident emission from both the neutron-star surface or
boundary layer and the corona that is responsible for the high-energy
emission in these systems. From the fits with the reflection model we
found that in four out of the six observations the main contribution to
the reflected spectrum comes from the neutron-star surface or boundary
layer, whereas in the other two observations the main contribution to
the reflected spectrum comes from the corona. We found that the relative
contribution of these two components is not correlated to the state of
the source. From the phenomenological models, we found that the iron
line profile is better described by a symmetric, albeit broad, profile.
The width of the line cannot be explained only by Compton broadening,
and we therefore explored the case of relativistic broadening. We
further found that the direct emission from the disc, boundary layer and
corona generally evolved in a manner consistent with the standard
accretion disc model, with the disc and boundary layer becoming hotter
and the disc moving inwards as the source changed from the hard to the
soft state. The iron line, however, did not appear to follow the same
trend.
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