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

Abstract

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.