On the dependence of the X-ray continuum variations with luminosity in accreting X-ray pulsars

Постнов, К. А.; Gornostaev, M. I.; Klochkov, D.; Laplace, E.; Lukin, V. V.; Шакура, Н. И.

doi:10.1093/mnras/stv1393

Cited by 64 publications

(88 citation statements)

References 37 publications

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“…This is in line with theoretical expectations by Postnov et al (2015a) for sources in the subcritical accretion regime. -If L brk,hi can indeed be associated with the source exceeding the critical luminosity, then parameter combinations can be found such that each of the three theories summarized in Appendix A predict the expected value for this luminosity correctly: -L brk,hi ∼L crit for w > 1.9 after Becker et al (2012, Eq.…”

Section: Accretion Regimes In Gro J1008−57supporting

confidence: 93%

“…A.4) for a filled accretion column with a radius of r 0 ≤ 935 m. The corresponding luminosity around 10 36 erg s −1 is, however, too low for the transition to supercritical accretion as expected by all these theories. Even Postnov et al (2015a) expect this transition to occur around 10 37 erg s −1 . -The ratio between the Coulomb braking and the critical luminosity, L coul /L crit , after Becker et al (2012, Eqs.…”

Section: Accretion Regimes In Gro J1008−57mentioning

confidence: 98%

“…Another recent theoretical investigation by Postnov et al (2015a) calculates the X-ray spectrum in the supercritical regime using the radiation diffusion approximation and assuming the emission emerging from the walls of the accretion column (known as the fan beam geometry). In this scenario the accretion column is assumed to be optically thick and the infalling matter is decelerated by a radiative shock similar to Becker et al (2012).…”

Section: Accretion Regimes In Gro J1008−57mentioning

confidence: 99%

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Evidence for different accretion regimes in GRO J1008−57

Kühnel

Fürst

Pottschmidt

et al. 2017

A&A

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We present a comprehensive spectral analysis of the BeXRB GRO J1008−57 over a luminosity range of three orders of magnitude using NuSTAR , Suzaku and RXTE data. We find significant evolution of the spectral parameters with luminosity. In particular the photon index hardens with increasing luminosity at intermediate luminosities between 10 36 -10 37 erg s −1 . This evolution is stable and repeatedly observed over different outbursts. However, at the extreme ends of the observed luminosity range, we find that the correlation breaks down, with a significance level of at least 3.7σ. We conclude that these changes indicate transitions to different accretion regimes, which are characterized by different deceleration processes, such as Coulomb or radiation breaking. We compare our observed luminosity levels of these transitions to theoretical predications and discuss the variation of those theoretical luminosity values with fundamental neutron star parameters. Finally, we present detailed spectroscopy of the unique "triple peaked" outburst in 2014/15 which does not fit in the general parameter evolution with luminosity. The pulse profile on the other hand is consistent with what is expected at this luminosity level, arguing against a change in accretion geometry. In summary, GRO J1008−57 is an ideal target to study different accretion regimes due to the well constrained evolution of its broad-band spectral continuum over several orders of magnitude in luminosity.

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Section: Accretion Regimes In Gro J1008−57supporting

confidence: 93%

Section: Accretion Regimes In Gro J1008−57mentioning

confidence: 98%

Section: Accretion Regimes In Gro J1008−57mentioning

confidence: 99%

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Evidence for different accretion regimes in GRO J1008−57

Kühnel

Fürst

Pottschmidt

et al. 2017

A&A

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“…In our best-fit model we tie the accretion columns dimensions to prevent parameter degeneracy. Such an asymmetric B-field configuration, however, may suggest columns of different sizes due to possible asymmentric accretion flows, that is different accretion rates for the two poles (see e.g., Becker & Wolff 2007;Postnov et al 2015). Therefore, and due to the fact that we make the very simple assumption of an homogeneously emitting surface, the obtained heights and radii of the columns should not be interpreted as physical quantities.…”

Section: Pulse Profile Modelingmentioning

confidence: 97%

Spectral and Timing Analysis of the Accretion-powered Pulsar 4U 1626–67 Observed with Suzaku and NuSTAR

Iwakiri

Pottschmidt

Falkner³

et al. 2019

ApJ

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We present an analysis of the spectral shape and pulse profile of the accretion-powered pulsar 4U 1626−67 observed with Suzaku and NuSTAR during a spin-up state. The pulsar, which experienced a torque reversal to spin-up in 2008, has a spin period of ∼7.7 s. Comparing the phase-averaged spectra obtained with Suzaku in 2010 and with NuSTAR in 2015, we find that the spectral shape changed between the two observations: the 3-10 keV flux increased by ∼5% while the 30-60 keV flux decreased significantly by ∼35%. Phase-averaged and phase-resolved spectral analysis shows that the continuum spectrum observed by NuSTAR is well described by an empirical NPEX continuum with an added broad Gaussian emission component around the spectral peak at ∼20 keV. Taken together with the observedṖ value obtained from Fermi/GBM, we conclude that the spectral change between the Suzaku and NuSTAR observations was likely caused by an increase of the accretion rate. We also report the possible detection of asymmetry in the profile of the fundamental cyclotron line. Furthermore, we present a study of the energyresolved pulse profiles using a new relativistic ray tracing code, where we perform a simultaneous fit to the pulse profiles assuming a two-column geometry with a mixed pencil-and fan-beam emission pattern. The resulting pulse profile decompositions enable us to obtain geometrical parameters of accretion columns (inclination, azimuthal and polar angles) and a fiducial set of beam patterns. This information is important to validate the theoretical predictions from radiation transfer in a strong magnetic field.

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“…Therefore, at low accretion rates Comptonization in the accretion channel is not expected to significantly affect the initial spectrum as well, so it is likely to remain relatively soft. The variations of spectral hardness and its correlation with the mass accretion rate for XRPs were discussed recently by Postnov et al (2015) in context of a reflection model (see Poutanen et al 2013).…”

Section: Spectral Changesmentioning

confidence: 99%

Propeller effect in two brightest transient X-ray pulsars: 4U 0115+63 and V 0332+53

Tsygankov

Lutovinov

Doroshenko

et al. 2016

A&A

105

111

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Aims. We present the results of the monitoring programmes performed with the Swift/XRT telescope and aimed specifically to detect an abrupt decrease of the observed flux associated with a transition to the propeller regime in two well-known X-ray pulsars 4U 0115+63 and V 0332+53. Methods. Both sources form binary systems with Be optical companions and undergo so-called giant outbursts every 3-4 years. The current observational campaigns were performed with the Swift/XRT telescope in the soft X-ray band (0.5-10 keV) during the declining phases of the outbursts exhibited by both sources in 2015.Results. The transitions to the propeller regime were detected at the threshold luminosities of (1.4 ± 0.4) × 10 36 erg s −1 and (2.0 ± 0.4) × 10 36 erg s −1 for 4U 0115+63 and V 0332+53, respectively. Spectra of the sources are shown to be significantly softer during the low state. In both sources, the accretion at rates close to the aforementioned threshold values briefly resumes during the periastron passage following the transition into the propeller regime. The strength of the dipole component of the magnetic field required to inhibit the accretion agrees well with estimates based on the position of the cyclotron lines in their spectra, thus excluding presence of a strong multipole component of the magnetic field in the vicinity of the neutron star.

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On the dependence of the X-ray continuum variations with luminosity in accreting X-ray pulsars

Cited by 64 publications

References 37 publications

Evidence for different accretion regimes in GRO J1008−57

Evidence for different accretion regimes in GRO J1008−57

Spectral and Timing Analysis of the Accretion-powered Pulsar 4U 1626–67 Observed with Suzaku and NuSTAR

Propeller effect in two brightest transient X-ray pulsars: 4U 0115+63 and V 0332+53

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