The accretion environment in Vela X-1 during a flaring period using<i>XMM-Newton</i>

Martínez-Núñez, Silvia; Torrejón, José M.; Kühnel, Matthias; Kretschmar, P.; Stuhlinger, M.; Roca, José Joaquín Rodes; Fürst, F.; Kreykenbohm, I.; Martín-Carrillo, A.; Pollock, A. M. T.; Wilms, J.

doi:10.1051/0004-6361/201322404

Cited by 43 publications

(93 citation statements)

References 31 publications

(51 reference statements)

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“…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).…”

Section: Double-peaked Sample Phase-resolved Spectroscopysupporting

confidence: 93%

“…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).…”

Section: Double-peaked Sample Phase-resolved Spectroscopymentioning

confidence: 96%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Malacaria

Mihara

Santangelo

et al. 2016

A&A

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Context. Vela X-1 is one of the best-studied and most luminous accreting X-ray pulsars. The supergiant optical companion produces a strong radiatively driven stellar wind that is accreted onto the neutron star, producing highly variable X-ray emission. A complex phenomenology that is due to both gravitational and radiative effects needs to be taken into account to reproduce orbital spectral variations. Aims. We have investigated the spectral and light curve properties of the X-ray emission from Vela X-1 along the binary orbit. These studies allow constraining the stellar wind properties and its perturbations that are induced by the pulsating neutron star. Methods. We took advantage of the All Sky Monitor MAXI/GSC data to analyze Vela X-1 spectra and light curves. By studying the orbital profiles in the 4−10 and 10−20 keV energy bands, we extracted a sample of orbital light curves (∼15% of the total) showing a dip around the inferior conjunction, that is, a double-peaked shape. We analyzed orbital phase-averaged and phase-resolved spectra of both the double-peaked and the standard sample. Results. The dip in the double-peaked sample needs N H ∼ 2 × 10 24 cm −2 to be explained by absorption alone, which is not observed in our analysis. We show that Thomson scattering from an extended and ionized accretion wake can contribute to the observed dip. Fit by a cutoff power-law model, the two analyzed samples show orbital modulation of the photon index that hardens by ∼0.3 around the inferior conjunction, compared to earlier and later phases. This indicates a possible inadequacy of this model. In contrast, including a partial covering component at certain orbital phase bins allows a constant photon index along the orbital phases, indicating a highly inhomogeneous environment whose column density has a local peak around the inferior conjunction. We discuss our results in the framework of possible scenarios.

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“…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).…”

Section: Double-peaked Sample Phase-resolved Spectroscopysupporting

confidence: 93%

Section: Double-peaked Sample Phase-resolved Spectroscopymentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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

Malacaria

Mihara

Santangelo

et al. 2016

A&A

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Giménez-García

Shenar

Torrejón

et al. 2016

A&A

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Context. Classical supergiant X-ray binaries (SGXBs) and supergiant fast X-ray transients (SFXTs) are two types of high-mass X-ray binaries (HMXBs) that present similar donors but, at the same time, show very different behavior in the X-rays. The reason for this dichotomy of wind-fed HMXBs is still a matter of debate. Among the several explanations that have been proposed, some of them invoke specific stellar wind properties of the donor stars. Only dedicated empiric analysis of the donors' stellar wind can provide the required information to accomplish an adequate test of these theories. However, such analyses are scarce. Aims. To close this gap, we perform a comparative analysis of the optical companion in two important systems: IGR J17544-2619 (SFXT) and Vela X-1 (SGXB). We analyze the spectra of each star in detail and derive their stellar and wind properties. As a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. Methods. We use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (NLTE) Potsdam Wolf-Rayet model atmosphere code. We derive the physical properties of the stars and their stellar winds, accounting for the influence of X-rays on the stellar winds. Results. We find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). The distance to the sources have been revised and also agree well with the estimations already available in the literature. In IGR J17544-2619 we are able to narrow the uncertainty to d = 3.0 ± 0.2 kpc. From the stellar radius of the donor and its X-ray behavior, the eccentricity of IGR J17544-2619 is constrained to e < 0.25. The derived chemical abundances point to certain mixing during the lifetime of the donors. An important difference between the stellar winds of the two stars is their terminal velocities ( ∞ = 1500 km s −1 in IGR J17544-2619 and ∞ = 700 km s −1 in Vela X-1), which have important consequences on the X-ray luminosity of these sources. Conclusions. The donors of IGR J17544-2619 and Vela X-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. In addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. However, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the X-ray luminosity of the sources. This specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in Vela X-1, while it favors an inhibiting accretion mechanism in IGR J17544-2619. Our study demonstrates that the relative wind velocity is critical in class determination for the HMXBs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion...

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“…⋆ 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).…”

Section: Introductionmentioning

confidence: 99%

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

Sidoli¹,

Paizis²,

Fürst³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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Vela X-1 is the prototype of the class of wind-fed accreting pulsars in high mass X-ray binaries hosting a supergiant donor. We have analysed in a systematic way ten years of IN-TEGRAL data of Vela X-1 (22-50 keV) and we found that when outside the X-ray eclipse, the source undergoes several luminosity drops where the hard X-rays luminosity goes below ∼3×10 35 erg s −1 , becoming undetected by INTEGRAL. These drops in the X-ray flux are usually referred to as "off-states" in the literature. We have investigated the distribution of these off-states along the Vela X-1 ∼8.9 d orbit, finding that their orbital occurrence displays an asymmetric distribution, with a higher probability to observe an off-state near the pre-eclipse than during the post-eclipse. This asymmetry can be explained by scattering of hard X-rays in a region of ionized wind, able to reduce the source hard X-ray brightness preferentially near eclipse ingress. We associate this ionized large-scale wind structure with the photoionization wake produced by the interaction of the supergiant wind with the X-ray emission from the neutron star. We emphasize that this observational result could be obtained thanks to the accumulation of a decade of INTEGRAL data, with observations covering the whole orbit several times, allowing us to detect an asymmetric pattern in the orbital distribution of off-states in Vela X-1.

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

Cited by 43 publications

References 31 publications

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

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

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

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

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