Journal Article

Superorbital variability in hard X-rays

S. A. Farrell, D. Barret and G. K. Skinner

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 393, issue 1, pages 139-156
Published in print February 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI:
Superorbital variability in hard X-rays

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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.

Keywords: accretion, accretion discs; stars: neutron; X-rays: binaries

Journal Article.  8958 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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