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XMM-Newton observations of polars in low accretion states

Gavin Ramsay·Mark Cropper·Kinwah Wu·Keith Mason·France Cordova·William Priedhorsky
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Abstract

We have made a series of snap-shot observations of 37 polars using XMM-Newton. We found that 16 of these systems were in a low, or much reduced, accretion state. Of those, 6 were not detected in X-rays. This suggests that in any survey of polars, around half will be in a low accretion state. We tested if there was a bias towards certain orbital periods: this is not the case. Of the 10 systems which were detected at low, but significant rates in X-rays, 8 showed significant variability in their X-ray light curves. This implies that non-uniform accretion still takes place during low accretion epochs. The bolometric luminosity of these systems is ~10^30 ergs s, two orders of magnitude less than for systems in a high accretion state. The X-ray spectra show no evidence of a distinct soft X-ray component. However, the X-ray and UV data imply that such a low temperature component exists: its temperature is low enough for its flux distribution to move outside the bandpass of the X-ray instruments.

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Gavin Ramsay, Mark Cropper, Kinwah Wu, Keith Mason, France Cordova, William Priedhorsky. 2004-02-23. XMM-Newton observations of polars in low accretion states. https://doi.org/10.1111/j.1365-2966.2004.07732.x

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