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Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1
High Energy Astrophysical Phenomena · Submitted 11 Jan 2022
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We see strong variability in absorption between the two observations and within one observation (for the ~0.36-0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion- and photoionisation wakes in the system and our variable line of sight through this structure.
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The abstract, sentence by sentence
Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability and convenient physical parameters (close distance, high inclination, small orbital separation) which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems to understand accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ~0.68-0.78 and ~0.36-0.52 which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period time-scale using a partially covered powerlaw continuum with a Fermi-Dirac cut-off to model the continuum and local absorption. We could confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We could not confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the ~0.36-0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion- and photoionisation wakes in the system and our variable line of sight through this structure.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability and convenient physical parameters (close distance, high inclination, small orbital separation) which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems to understand accretion processes in high-mass X-ray binaries on all scales. | background 1.00 | 0.06 | 0.04 | asserted 1.00 |
| s1 | We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ~0.68-0.78 and ~0.36-0.52 which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. | contribution 0.56 | 0.97 | 0.05 | asserted 1.00 |
| s2 | We follow the evolution of spectral parameters down to the pulse period time-scale using a partially covered powerlaw continuum with a Fermi-Dirac cut-off to model the continuum and local absorption. | method 1.00 | 0.95 | 0.05 | asserted 0.95 |
| s3 | We could confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. | result 0.64 | 0.96 | 0.21 | hedged possibility 0.62 |
| s4 | We could not confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. | result 1.00 | 0.95 | 0.15 | asserted 0.75 |
| s5 | We see strong variability in absorption between the two observations and within one observation (for the ~0.36-0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion- and photoionisation wakes in the system and our variable line of sight through this structure. | interpretation 0.55 | 0.95 | 0.21 | asserted 0.55 |
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The paper
Original abstract
Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability and convenient physical parameters (close distance, high inclination, small orbital separation) which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems to understand accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ~0.68-0.78 and ~0.36-0.52 which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period time-scale using a partially covered powerlaw continuum with a Fermi-Dirac cut-off to model the continuum and local absorption. We could confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We could not confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the ~0.36-0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion- and photoionisation wakes in the system and our variable line of sight through this structure.
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References
How the literature uses it
4 arXiv papers cite this in 9 sentences
Papers citing it · 3 sentences without a confident label
Contests it 1 paper
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It should be noted that the so-called 10 keV broad absorption feature in Vela X-1 reported by the NuStar observations (e.g. [ref] ) cannot be confirmed by the Insight-HXMT data.
Variations of cyclotron resonant scattering features in Vela X-1 revealed with Insight-HXMT · Phase averaged spectral analysis · contest 0.74
Uses its data or values 2 papers
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We used the simultaneous XMM-Newton and NuSTAR dataset already analysed by [ref] and [ref] .
Energy-resolved pulse profiles of Vela X-1: cross-calibrating XMM-Newton and NuSTAR to trace spectral features · Observations and data extraction · 1.00
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The bin value is selected to match the pulse period of $P=283.4447 ±0.0004$ s derived in [ref] .
SAS in ESA Datalabs: A New Platform for XMM-Newton Analysis · Method & Set-up · 1.00
Compares with it 1 paper
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The higher-energy feature is centered at $E_2=55.1_-0.5^+0.6$ keV with a width $σ_2=2.1_-0.5^+0.6$ keV, consistent with the harmonic CRSF whose centroid varies between $∼$ 52 and $∼$ 56 keV across different NuSTAR observations [ref] .
Energy-resolved pulse profiles of Vela X-1: cross-calibrating XMM-Newton and NuSTAR to trace spectral features · Hard-band modeling (10–70 keV) · 0.95
Cites it as background 1 paper
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They can be effectively modeled by an additional broad Gaussian component, with a centroid energy of $∼10 keV$, either in emission [ref] or in absorption [ref] , commonly referred to as the “10 keV feature.”
Flux variability of the "10 keV feature" of 4U 0115+63 · Introduction · 0.85
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