Publication Date:
2003
abstract:
Observations of two unclassified Low Mass
X-ray Binaries, X1543-624 and
X1556-605, are presented. In the 2-10 keV
band the first of the two
sources is a factor of two stronger than
the other. Both sources do not
show X-ray bursts, dips or eclipses in
their X-ray light curves. We find
that both spectra are described by a
two-component model consisting of
emission from a cool accretion disk plus a
Comptonized blackbody with
kT_{bb} ~ 1.5 keV in a low opacity plasma.
The spectrum of X1543-624
hardens from the first to the second
observation, when the source slowly
moves from right to left in the
colour-colour diagram. The spectrum of
X1556-605 can also be described by a model
consisting of a blackbody plus
an unsaturated Comptonization with electron
energy kT_{e} ~ 4 keV. In the
first observation, X1543-624 shows evidence
of a Fe K emission line at 6.4
keV. Moreover, in both observations, the
source spectrum exhibits an
emission feature around 0.7 keV, which is
interpreted as due to the
superposition of the K edge absorption
features of O and Ne elements with
uncommon relative abundances with respect
to the solar one (O/O_{sun} ~
0.3, Ne/Ne_{sun} ~ 2.5). In the spectrum of
X1556-605 no emission lines
are observed. We discuss these results and
their implications for the
source classification and the accretion
geometry of the compact object.
Iris type:
01.01 Articolo in rivista
List of contributors: