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arXiv · 0810.0432

Variations in the dip properties of the low-mass X-ray binary XB 1254-69 observed with XMM-Newton and INTEGRAL

M. Diaz Trigo·A. N. Parmar·L. Boirin·C. Motch·A. Talavera·S. Balman
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Abstract

We have analysed data from five XMM-Newton observations of XB 1254-69, 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. At high (1-4 s) time resolution ``shallow dips'' are seen to include a few, very rapid, deep dips whilst the ``deep'' dips consist of many similar very rapid, deep, fluctuations. 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 fit 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 modified 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 (kT ~ 1.8 keV) when deep dips are present and warmest (kT ~ 2.1 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. We provide a revised estimate of the orbital period of 0.16388875 +/- 0.00000017 day.

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M. Diaz Trigo, A. N. Parmar, L. Boirin, C. Motch, A. Talavera, S. Balman. 2008-10-02. Variations in the dip properties of the low-mass X-ray binary XB 1254-69 observed with XMM-Newton and INTEGRAL. https://doi.org/10.1051/0004-6361%3A200810154

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