Journal Article

Quiescent X-ray variability from the neutron star transient Aql X-1

E. M. Cackett, J. K. Fridriksson, J. Homan, J. M. Miller and R. Wijnands

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 414, issue 4, pages 3006-3013
Published in print July 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18601.x
Quiescent X-ray variability from the neutron star transient Aql X-1

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A number of studies have revealed variability from neutron star low-mass X-ray binaries during quiescence. Such variability is not well characterized, or understood, but may be a common property that has been missed due to lack of multiple observations. One such source where variability has been observed is Aql X-1. Here, we analyse 14 Chandra and XMM–Newton observations of Aql X-1 in quiescence, covering a period of approximately 2 yr. There is clear variability between the epochs, with the most striking feature being a flare-like increase in the flux by a factor of 5. Spectral fitting is inconclusive as to whether the power-law and/or thermal component is variable. We suggest that the variability and flare-like behaviour during quiescence is due to accretion at low rates which might reach the neutron star surface.

Keywords: accretion, accretion discs; stars: individual: Aql X-1; stars: neutron; X-rays: binaries

Journal Article.  5580 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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