Supergiant Fast X-ray Transients uncovered by the EXTraS project: flares reveal the development of magnetospheric instability in accreting neutron stars

Abstract

The low luminosity, X-ray flaring activity, of the sub-class of high mass X-ray binaries called Supergiant Fast X-ray Transients, has been investigated using XMM-Newton public observations, taking advantage of the products made publicly available by the EXTraS project. One of the goals of EXTraS was to extract from the XMM-Newton public archive information on the aperiodic variability of all sources observed in the soft X-ray range with EPIC (0.2-12 keV). Adopting a Bayesian block decomposition of the X-ray light curves of a sample of SFXTs, we picked out 144 X-ray flares, covering a large range of soft X-ray luminosities (1e32-1e36 erg/s). We measured temporal quantities, like the rise time to and the decay time from the peak of the flares, their duration and the time interval between adjacent flares. We also estimated the peak luminosity, average accretion rate and energy release in the flares. The observed soft X-ray properties of low-luminosity flaring activity from SFXTs is in qualitative agreement with what is expected by the application of the Rayleigh-Taylor instability model in accreting plasma near the neutron star magnetosphere. In the case of rapidly rotating neutron stars, sporadic accretion from temporary discs cannot be excluded.

Accepted for publication in MNRAS (accepted 2019 May 1; received 2019 April 30; in original form 2019 February 25). 22 pages, 16 figures, 3 tables)

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Cited by in corpus (11)

• The EXTraS Project: Exploring the X-ray transient and variable sky
• NuSTAR observation of the Supergiant Fast X-ray Transient IGR J11215-5952 during its 2017 outburst
• Monitoring clumpy wind accretion in supergiant fast X-ray transients with XMM-Newto
• The 100-month Swift catalogue of supergiant fast X-ray transients II. SFXT diagnostics from outburst properties
• Self-organized critical characteristics of teraelectronvolt photons from GRB 221009A
• Capturing the lowest luminosity state of the Supergiant Fast X-ray Transient XTE J1739-302
• Detecting the intrinsic X-ray emission from the O-type donor star and the residual accretion in a Supergiant Fast X-ray Transient during its faintest state
• Clumpy wind studies and the non-detection of cyclotron line in OAO 1657-415
• Cyclical accretion regime change in the slow X-ray pulsar 4U 0114+65 observed with Chandra
• Monitoring the X-ray Variability of Bright X-ray Sources in M33
• 4XMM J181330.1-175110: a new supergiant fast X-ray transient