The accretion environment in Vela X-1 during a flaring period usingXMM-Newton

Abstract

We present analysis of 100 ks contiguous XMM-Newton data of the prototypical wind accretor Vela X-1. The observation covered eclipse egress between orbital phases 0.134 and 0.265, during which a giant flare took place, enabling us to study the spectral properties both outside and during the flare. This giant flare with a peak luminosity of 3.92 +0.42 −0.09 × 10 37 erg s −1 allows estimates of the physical parameters of the accreted structure with a mass of ∼10 21 g. We have been able to model several contributions to the observed spectrum with a phenomenological model formed by three absorbed power laws plus three emission lines. After analysing the variations with orbital phase of the column density of each component, as well as those in the Fe and Ni fluorescence lines, we provide a physical interpretation for each spectral component. Meanwhile, the first two components are two aspects of the principal accretion component from the surface of the neutron star, the third component seems to be the X-ray light echo formed in the stellar wind of the companion.

Probing the stellar wind environment of Vela X–1 with MAXI

“…This is consistent with observations which showed that flares in Vela X-1 last from 10 2 s up to 10 4 s (see Ducci et al 2009;Martínez-Núñez et al 2014, and references therein).…”

“…Inhomogeneous stellar winds from supergiant stars (so-called clumps) are expected (Runacres & Owocki 2005) and observed (Goldstein et al 2004, and references therein), and have been suggested as the cause for Vela X-1 flaring activity (see Kreykenbohm et al 2008 andMartínez-Núñez et al 2014). The timescale on which clumps hit the X-ray pulsar is on the order of the wind's dynamic timescale 0.5R B v ∞ ∼ 10 11 cm 1100 km s −1 ∼ 1000 s (2) where 0.5R B is the average separation between clumps (Sundqvist et al 2010).…”

“…However, it is typical of Vela X-1 to show "off-states" in which it becomes faint for several 10 2 −10 3 s, and "giant flares", when the source flux suddenly increases up to a factor of 20 (Kreykenbohm et al 2008;Sidoli et al 2015). Density inhomogeneities are observed in the matter during the accretion stage (see Martínez-Núñez et al 2014, and references therein) and are considered a possible reason for the observed X-ray flux variability.…”

Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries

“…These sources are usually considered to be prototypical for their respective classes (Martínez-Núñez et al 2014;Sidoli et al 2009;Mauche et al 2007). Hence, in addition to the important scientific value of studying these sources by themselves, this is an excellent opportunity to compare the donor parameters in these two prototypical systems, and to test how well the aforementioned resolutions for the SFXT puzzle fit with our results.…”

Probing large-scale wind structures in Vela X–1 using off-states with INTEGRAL

“…⋆ E-mail: sidoli@iasf-milano.inaf.it 1992, Sako et al 1999, Schulz et al 2002, Goldstein et al 2004, Watanabe et al 2006, Fürst et al 2010, Doroshenko et al 2013, Martínez-Núñez et al 2014 and references therein). These studies indicate the presence of both cold and hot gas components in the system, consistent with photoionization of the stellar wind produced by the X-ray pulsar, leading to the formation of a so-called photoionization wake trailing the neutron star (Fransson & Fabian 1980, Kaper et al 1994, Feldmeier et al 1996, van Loon et al 2001, confirmed by simulations (Blondin et al 1990, Blondin et al 1991, Mauche et al 2008).…”