Understanding the coexistence of spin-up and spin-down behaviours in long-period X-ray pulsars

Wang, W; Tong, H.

doi:10.1093/mnras/stz3459

Cited by 18 publications

(12 citation statements)

References 68 publications

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“…Alternatively, this overbraking could be indicative of a phase in the past in which stellar material was supplied to the neutron star at a much lower rate than today, and with a high amount of specific angular momentum, which is suggestive of a slow wind (Wang & Tong 2020;Ho et al 2020). The system would have been in the propeller regime, and the neutron star would have spun down until the mass accretion rate suddenly increased by so much that the magnetospheric radius became smaller than the corotation radius, as is currently observed if the magnetic field measured through CRSFs is accurate.…”

Section: Magnetospheric Accretion and Induced Torquesmentioning

confidence: 99%

Revisiting the archetypical wind accretor Vela X-1 in depth

Kretschmar

Mellah

Martínez-Núñez

et al. 2021

A&A

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Context. The Vela X-1 system is one of the best-studied X-ray binaries because it was detected early, has persistent X-ray emission, and a rich phenomenology at many wavelengths. The system is frequently quoted as the archetype of wind-accreting high-mass X-ray binaries, and its parameters are referred to as typical examples. Specific values for these parameters have frequently been used in subsequent studies, however, without full consideration of alternatives in the literature, even more so when results from one field of astronomy (e.g., stellar wind parameters) are used in another (e.g., X-ray astronomy). The issues and considerations discussed here for this specific, very well-known example will apply to various other X-ray binaries and to the study of their physics. Aims. We provide a robust compilation and synthesis of the accumulated knowledge about Vela X-1 as a solid baseline for future studies, adding new information where available. Because this overview is targeted at a broader readership, we include more background information on the physics of the system and on methods than is usually done. We also attempt to identify specific avenues of future research that could help to clarify open questions or determine certain parameters better than is currently possible. Methods. We explore the vast literature for Vela X-1 and on modeling efforts based on this system or close analogs. We describe the evolution of our knowledge of the system over the decades and provide overview information on the essential parameters. We also add information derived from public data or catalogs to the data taken from the literature, especially data from the Gaia EDR3 release. Results. We derive an updated distance to Vela X-1 and update the spectral classification for HD 77518. At least around periastron, the supergiant star may be very close to filling its Roche lobe. Constraints on the clumpiness of the stellar wind from the supergiant star have improved, but discrepancies persist. The orbit is in general very well determined, but a slight difference exists between the latest ephemerides. The orbital inclination remains the least certain factor and contributes significantly to the uncertainty in the neutron star mass. Estimates for the stellar wind terminal velocity and acceleration law have evolved strongly toward lower velocities over the years. Recent results with wind velocities at the orbital distance in the range of or lower than the orbital velocity of the neutron star support the idea of transient wind-captured disks around the neutron star magnetosphere, for which observational and theoretical indications have emerged. Hydrodynamic models and observations are consistent with an accretion wake trailing the neutron star. Conclusions. With its extremely rich multiwavelength observational data and wealth of related theoretical studies, Vela X-1 is an excellent laboratory for exploring the physics of accreting X-ray binaries, especially in high-mass systems. Nevertheless, much room remains to improve the accumulated knowledge. On the observational side, well-coordinated multiwavelength observations and observing campaigns addressing the intrinsic variability are required. New opportunities will arise through new instrumentation, from optical and near-infrared interferometry to the upcoming X-ray calorimeters and X-ray polarimeters. Improved models of the stellar wind and flow of matter should account for the non-negligible effect of the orbital eccentricity and the nonspherical shape of HD 77581. There is a need for realistic multidimensional models of radiative transfer in the UV and X-rays in order to better understand the wind acceleration and effect of ionization, but these models remain very challenging. Improved magnetohydrodynamic models covering a wide range of scales are required to improve our understanding of the plasma-magnetosphere coupling, and they are thus a key factor for understanding the variability of the X-ray flux and the torques applied to the neutron star. A full characterization of the X-ray emission from the accretion column remains another so far unsolved challenge.

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Section: Magnetospheric Accretion and Induced Torquesmentioning

confidence: 99%

Revisiting the archetypical wind accretor Vela X-1 in depth

Kretschmar

Mellah

Martínez-Núñez

et al. 2021

A&A

View full text Add to dashboard Cite

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“…Finally, although our estimates of the spin period were inconclusive in terms of the spin evolution of the pulsar, future monitoring programs are essential for determining whether the pulsar is spinning up or down. It has been proposed that long-period pulsars with magnetar-like field strengths could exhibit a spin up trend due to the decay of the B field of the NS (Wang & Tong 2020). A future measurement of the spin evolution will therefore provide crucial information about the nature of the NS.…”

Section: A Highly Magnetised Slowly Rotating Neutron Star?mentioning

confidence: 99%

Fast flaring observed from XMMU J053108.3−690923 by eROSITA: a supergiant fast X-ray transient in the Large Magellanic Cloud

Maitra

Haberl

Vasilopoulos³

et al. 2021

A&A

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Context. Supergiant fast X-ray transients (SFXTs) are a peculiar class of supergiant high-mass X-ray binary (HMXB) systems characterised by extreme variability in the X-ray domain. In current models, this is mainly attributed to the clumpy nature of the stellar wind coupled with gating mechanisms involving the spin and magnetic field of the neutron star. Aims. We studied the X-ray properties of the supergiant HMXB XMMU J053108.3−690923 in the Large Magellanic Cloud to understand its nature. Methods. We performed a detailed temporal and spectral analysis of the eROSITA and XMM-Newton data of XMMU J053108.3−690923. Results. We confirm the putative pulsations previously reported for the source with high confidence, certifying its nature as a neutron star in orbit with a supergiant companion. We identify the extremely variable nature of the source in the form of flares seen in the eROSITA light curves. The source flux exhibits a total dynamic range of more than three orders of magnitude, which confirms its nature as an SFXT, and is the first such direct evidence from a HMXB outside our Galaxy exhibiting a very high dynamic range in luminosity as well as a fast flaring behaviour. We detect changes in the hardness ratio during the flaring intervals where the hardness ratio reaches its minimum during the peak of the flare and increases steeply shortly afterwards. This is also supported by the results of the spectral analysis carried out at the peak and off-flare intervals. This scenario is consistent with the presence of dense structures in the supergiant wind of XMMU J053108.3−690923 where the clumpy medium becomes photoionised at the peak of the flare leading to a drop in the photo-electric absorption. Further, we provide an estimate of the clumpiness of the medium and the magnetic field of the neutron star assuming a spin equilibrium condition.

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“…Observations of X-ray pulsars have indicated that they have spin periods ranging from milli-seconds (for example, SAX J1808.4+3658, Wijnands & van der Klis 1998) all the way up to a few thousand seconds (for example, 4U2206+54, 2S 0114+65, see Wang & Tong 2020). In fact, recent studies have indicated that the Be X-ray binary population comprises of two sub populations based on their spin and orbital periods and orbital eccentricities (Knigge, Coe & Podsiadlowski 2011): i) the short spin Pspin ∼ 10 s, P orb ∼40 d, and ii) Pspin ∼ 200 s, P orb ≈ 100 d (Prišegen 2020).…”

Section: Introductionmentioning

confidence: 99%

AstroSat detection of a mHz QPO and cyclotron line in IGR J19294+1816 during the 2019 outburst

Raman,

Paul,

Bhattacharya

2021

Preprint

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We present results from timing and spectral analysis of the HMXB X-ray pulsar IGR J19294+1816 observed using AstroSat during its recent Type-I outburst in October, 2019. AstroSat observations sampled the outburst at the decline phase right after the outburst peak. We carried out timing analysis on the light curves obtained using the Large Area X-ray Proportional Counter (LAXPC) instrument on board AstroSat and measured a spin period of 12.485065±0.000015 s. The peak in the power density spectrum (PDS) corresponding to the spin period of 12.48 s also shows a broadened base. We also detected a Quasi Periodic Oscillation (QPO) feature at 0.032±0.002 Hz with an RMS fractional amplitude of ∼18% in the PDS. We further carried out a joint spectral analysis using both the Soft X-ray Telescope (SXT) and the LAXPC instruments and detected a Cyclotron Resonant Scattering Feature (CRSF) at 42.7±0.9 keV and an Fe emission line at 6.4±0.1 keV. IGR J19294+1816, being an intermediate spin pulsar, has exhibited a plethora of spectral and timing features during its most recent 2019 outburst, adding it to the list of transients that exhibit both a QPO as well as a CRSF.

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Understanding the coexistence of spin-up and spin-down behaviours in long-period X-ray pulsars

Cited by 18 publications

References 68 publications

Revisiting the archetypical wind accretor Vela X-1 in depth

Revisiting the archetypical wind accretor Vela X-1 in depth

Fast flaring observed from XMMU J053108.3−690923 by eROSITA: a supergiant fast X-ray transient in the Large Magellanic Cloud

AstroSat detection of a mHz QPO and cyclotron line in IGR J19294+1816 during the 2019 outburst

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