出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We have analysed data from ve XMM-Newton observations of XB1254690, one of them simultaneous
with INTEGRAL, to investigate the mechanism responsible for the highly variable
dips durations and depths seen from this low-mass X-ray binary. Deep dips were present during
two observations, shallow dips during one and no dips were detected during the remaining two
observations. The folded V-band Optical Monitor light curves obtained when the source was undergoing
deep, shallow and no detectable dipping exhibit sinusoid-like variations with different
amplitudes and phases. We t EPIC spectra obtained from "persistent" or dip-free intervals with a
model consisting of disc-blackbody and thermal comptonisation components together with Gaussian
emission features at 1 and 6.6 keV modied by absorption due to cold and photo-ionised
material. None of the spectral parameters appears to be strongly correlated with the dip depth
except for the temperature of the disc blackbody which is coolest (kT1.8 keV) when deep dips
are present and warmest (kT2.1 keV) when no dips are detectable. We propose that the changes
in both disc temperature and optical modulation could be explained by the presence of a tilted
accretion disc in the system.
