Superorbital variability in hard X-rays

We present the results of a study with the Swift Burst Alert Telescope in the 14–195 keV range of the long-term variability of five low-mass X-ray binaries with reported or suspected superorbital periods – 4U 1636−536, 4U 1820−303, 4U 1916−053, Cyg X-2 and Sco X-1. No significant persistent periodic...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2009, Vol.393 (1), p.139-156
Main Authors: Farrell, S. A., Barret, D., Skinner, G. K.
Format: Article
Language:English
Subjects:
accretion
accretion discs
Accretion disks
accretion, accretion discs
Astronomy
Double stars
Earth, ocean, space
Exact sciences and technology
Orbits
stars: neutron
X-ray astronomy
X-rays: binaries
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Summary:We present the results of a study with the Swift Burst Alert Telescope in the 14–195 keV range of the long-term variability of five low-mass X-ray binaries with reported or suspected superorbital periods – 4U 1636−536, 4U 1820−303, 4U 1916−053, Cyg X-2 and Sco X-1. No significant persistent periodic modulation was detected around the previously reported periods in the 4U 1916−053, Cyg X-2 or Sco X-1 light curves. The ∼170-d period of 4U 1820−303 was detected up to 24 keV, consistent with variable accretion due to the previously proposed triple system model. The ∼46-d period in 4U 1636−536 was detected up to 100 keV, with the modulation in the low- and high-energy bands found to be phase shifted by ∼180° with respect to each other. This phase shift, when taken together with the near-coincident onset of the ∼46-d modulation and the low/hard X-ray state, leads us to speculate that the modulation could herald transient jet formation.
ISSN:0035-8711
1365-2966
DOI:10.1111/j.1365-2966.2008.14167.x