New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
Abstract
XMM-Newton observations of the supergiant fast X-ray transient IGR J17544-2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272 ± 0.0004 d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM-Newton observations (each lasting ∼15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544-2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033 erg s-1 (0.5-10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544-2619 dropped to ∼4 × 1032 erg s-1 (0.5-10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544-2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544-2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the `quasi-spherical accretion' model provides a good description of the behaviour of IGR J17544-2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2014
- DOI:
- 10.1093/mnras/stu110
- arXiv:
- arXiv:1401.3570
- Bibcode:
- 2014MNRAS.439.2175D
- Keywords:
-
- accretion;
- accretion discs;
- stars: winds;
- outflows;
- X-rays: binaries;
- X-rays: individual: IGR J17544-2619;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 12 pages, 5 figures, accepted for publication in MNRAS