An INTEGRAL overview of High-Mass X–ray Binaries: classes or transitions?

Abstract

We analyzed in a systematic way the public INTEGRAL observations spanning from December 2002 to September 2016, to investigate the hard X-ray properties of about 60 High Mass X-ray Binaries (HMXBs). We considered both persistent and transient sources, hosting either a Be star (Be/XRBs) or a blue supergiant companion (SgHMXBs, including Supergiant Fast X-ray Transients, SFXTs), a neutron star or a black hole. INTEGRAL X-ray light curves (18-50 keV), sampled at a bin time of about 2 ks, were extracted for all HMXBs to derive the cumulative distribution of their hard X-ray luminosity, their duty cycle, the range of variability of their hard X-ray luminosity. This allowed us to obtain an overall and quantitative characterization of the long-term hard X-ray activity of the HMXBs in our sample. Putting the phenomenology observed with INTEGRAL into context with other known source properties (e.g. orbital parameters, pulsar spin periods) together with observational constraints coming from softer X-rays (1-10 keV), enabled the investigation of the way the different HMXB subclasses behave (and sometimes overlap). For given source properties, the different sub-classes of massive binaries seem to cluster in a suggestive way. However, for what concerns supergiant systems (SgHMXBs versus SFXTs), several sources with intermediate properties exist, suggesting a smooth transition between the two sub-classes.

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

“…4 This resulted in a conversion factor of 10 −11 erg cm −2 count −1 (EPIC pn). Then, the flare peak X-ray luminosities have been calculated assuming the source distances reported by Sidoli & Paizis (2018) and listed in Table 2, for clarity. The luminosity is also reported in the y-axis, on the right side of the graphs in Figs.…”

Neutron Stars and Black Holes in the Small Magellanic Cloud: The SMC NuSTAR Legacy Survey

“…Completing a full population study of XRBs in the Milky Way is challenging due to the wide range of distances to these systems and reddening because of dust in the Milky Way disk. There has been some successful work (e.g., Grimm et al 2002;Bodaghee et al 2012;Lutovinov et al 2013;Sidoli & Paizis 2018), but it is difficult to survey a whole population down to a low enough L X to observe the quiescent population of XRBs. Recent surveys of the Galactic center and Norma arm with NuSTAR have added to our understanding of the Galactic XRB population at hard X-ray energies (Hong et al 2016;Fornasini et al 2017).…”

Investigating High Mass X-ray Binaries at hard X-rays with INTEGRAL

“…The advantage of the adoption of a long-term archive, analysed here in a systematic way, is that we are confident that the source duty cycles are close to the real source activity, above the INTEGRAL sensitivity. We refer the reader to Sidoli & Paizis (2018) for a detailed discussion of the possible observational biases. Cumulative Luminosity Distributions.…”