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EXOSAT and Ginga observations of interacting binary stars.

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posted on 19.11.2015, 09:16 by Mark Henry. Jones
X-ray observations of three classes of interacting binary are presented. The systems studied are believed to be undergoing mass transfer by Roche lobe overflow onto a compact object. The observations were made between 1983 and 1989 with the EXOSAT and Ginga satellite observatories. The dwarf nova SS Cygni was subject to extensive monitoring using EXOSAT. In quiescence, the source has a hard spectrum which shows thermal iron K? and possibly K? emission. In outburst, emission is dominated by a soft component which emits at energies below ∼ 1 keV. This soft emission shows large amplitude, quasi-coherent sinusoidal modulation at periods in the range 7.4 to 10.8 sec. The evolution of the properties of this oscillation through outburst are studied in detail. A two day Ginga observation of the x-ray pulsar 1E 2259+586 is described. The pulse arrival times were searched for orbited modulation, and an upper limit (3?) to the projected semi-major axis was found to be ar sin i < 140 It-msec for periods from 1000 to 5000 sec. The source spectrum shows a broad line feature at ∼ 7 keV. It is suggested that this may arise from cyclotron processes. Details axe given of the Ginga observations of low mass x-ray binary systems which show 'dip' variability, the sources being XB 1916-053, XBT 0748-676, and X 1624-490. A re-analysis of the EXOSAT observations of X 1624-490 is also presented. Modulation in dippers arises from occultation of the compact x-ray emitting regions by structure in the accretion disc. Timing measurements constrain on the size of the emitting region and the distribution of the obscuring material. Spectral changes in dip events require a two-component model of absorption. By simulation, it is shown that this behaviour may arise from single component absorption if the column density changes rapidly. Revised estimates for the metal abundances of the three sources are given.


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Physics and Astronomy

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University of Leicester

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