Open AccessXMM–Newton observations of polars in low accretion states
Author(s) -
Ramsay Gavin,
Cropper Mark,
Wu Kinwah,
Mason K. O.,
Córdova F. A.,
Priedhorsky W.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07732.x
Subject(s) - physics , astrophysics , accretion (finance) , light curve , accretion disc , flux (metallurgy) , luminosity , astronomy , spectral line , galaxy , materials science , metallurgy
ABSTARCT 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, six 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 that were detected at low but significant rates in X‐rays, eight 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 erg s −1 , 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.