Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304−1 with<i>RXTE</i>

Rothschild, R. E.; Kuehnel, M.; Pottschmidt, K.; Hemphill, Paul; Постнов, К. А.; Gornostaev, M. I.; Шакура, Н. И.; Fuerst, F.; Wilms, J.; Staubert, R.; Klochkov, D.

doi:10.1093/mnras/stw3222

Cited by 41 publications

(50 citation statements)

References 51 publications

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“…In the case of Swift J0243.6+6124 , the continuum from NuSTAR data was found to be described with NPEX or HECut model along with a hot blackbody at ∼3 keV. A blackbody component associated with a continuum model was also detected in other pulsars such as EXO 2030+375 (Reig & Coe 1999), RX J0440.9+4431 (Ferrigno et al 2013), GX 304-1 (Rothschild et al 2017) and GX 1+4 (Yoshida et al 2017). Assuming a distance of 2.5 kpc, the size of blackbody emitting region was calculated to be ≈325 m. This value is relatively small and consistent with the typical size of accretion column.…”

Section: Discussionmentioning

confidence: 90%

Understanding the spectral and timing behaviour of a newly discovered transient X-ray pulsar Swift J0243.6+6124

Jaisawal

Naik

Chenevez

2017

Monthly Notices of the Royal Astronomical Society

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We present the results obtained from timing and spectral studies of the newly discovered accreting X-ray binary pulsar Swift J0243.6+6124 using a NuSTAR observation in 2017 October at a flux level of ∼280 mCrab. Pulsations at 9.85423(5) s were detected in the X-ray light curves of the pulsar. Pulse profiles of the pulsar were found to be strongly energy dependent. A broad profile at lower energies was found to evolve into a double peaked profile in 30keV. The 3-79 keV continuum spectrum of the pulsar was well described with a negative and positive exponential cutoff or high energy cutoff power law models modified with a hot blackbody at ∼3 keV. An iron emission line was also detected at 6.4 keV in the source spectrum. We did not find any signature of cyclotron absorption line in our study. Results obtained from phase-resolved and time-resolved spectroscopy are discussed in the paper.

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Section: Discussionmentioning

confidence: 90%

Understanding the spectral and timing behaviour of a newly discovered transient X-ray pulsar Swift J0243.6+6124

Jaisawal

Naik

Chenevez

2017

Monthly Notices of the Royal Astronomical Society

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“…The second model associates shifts of the CRSF energy with changes of the height of a collisionless shock above the NS polar cap (Rothschild et al 2017). For the dipole field, the decrease of line energy from ∼60 to 15 keV implies an increase of the height of the line forming region by half a NS radius.…”

Section: Cyclotron Linementioning

confidence: 99%

Dramatic spectral transition of X-ray pulsar GX 304−1 in low luminous state

Tsygankov

Escorial

Suleimanov

et al. 2018

Monthly Notices of the Royal Astronomical Society: Letters

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We report on the discovery of a dramatic change in the energy spectrum of the Xray pulsar GX 304−1 appearing at low luminosity. Particularly, we found that the cutoff power-law spectrum typical for accreting pulsars, including GX 304−1 at higher luminosities of L X ∼ 10 36 −10 37 erg s −1 , transformed at lower luminosity of L X ∼ 10 34 erg s −1 to a two-component spectrum peaking around 5 and 40 keV. We suggest that the observed transition corresponds to a change of the dominant mechanism responsible for the deceleration of the accretion flow. We argue that the accretion flow energy at low accretion rates is released in the atmosphere of the neutron star, and the low-energy component in the source spectrum corresponds to the thermal emission of the optically thick, heated atmospheric layers. The most plausible explanations for the high-energy component are either the cyclotron emission reprocessed by the magnetic Compton scattering or the thermal radiation of deep atmospheric layers partly Comptonized in the overheated upper layers. Alternative scenarios are also discussed.

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“…This is likely to be the main stopping agent of the accretion flow when the photon luminosities are low enough for radiation pressure to be unimportant for the accretion flow breaking (but in the CRSF, where the optical depth is very high even at low luminosities, see Bykov & Krasilshchikov (2004)). This model has recently been used to describe the observed non-linear dependencies of the CRSF parameters on luminosity in another subcritical X-ray pulsar GX 304−1 (Rothschild et al 2017). We develop this model in more detail so that it can also be used to describe the evolution of the spectral hardness ratio (HR) with luminosity.…”

Section: Colissionless Shock Modelmentioning

confidence: 99%

Luminosity-dependent changes of the cyclotron line energy and spectral hardness in Cepheus X-4

Vybornov

Klochkov

Gornostaev

et al. 2017

A&A

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Context. X-ray spectra of accreting pulsars are generally observed to vary with their X-ray luminosity. In particular, the hardness of the X-ray continuum is found to depend on luminosity. In a few sources, the correlation between the energy of the cyclotron resonance scattering feature (CRSF) and the luminosity is clear. Different types (signs) of the correlation are believed to reflect different accretion modes. Aims. We analyse two NuSTAR observations of the transient accreting pulsar Cep X-4 during its 2014 outburst. Our analysis is focused on a detailed investigation of the dependence of the CRSF energy and of the spectral hardness on X-ray luminosity, especially on short timescales. Methods. To investigate the spectral changes as a function of luminosity within each of the two observations, we used the intrinsic variability of the source on the timescale of individual pulse cycles (tens of seconds) , the so-called pulse-to-pulse variability. Results. We find that the NuSTAR spectrum of Cep X-4 contains two CRSFs: the fundamental line at~30 keV and its harmonic at~55 keV. We find for the first time that the energy of the fundamental CRSF increases and the continuum becomes harder with increasing X-ray luminosity not only between the two observations, that is, on the long timescale, but also within an individual observation, on the timescale of a few tens of seconds. We investigate these dependencies in detail including their non-linearity. We discuss a possible physical interpretation of the observed behaviour in the frame of a simple one-dimensional model of the polar emitting region with a collisionless shock formed in the infalling plasma near the neutron star surface. With this model, we are able to reproduce the observed variations of the continuum hardness ratio and of the CRSF energy with luminosity.

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Discovery and modelling of a flattening of the positive cyclotron line/luminosity relation in GX 304−1 withRXTE

Cited by 41 publications

References 51 publications

Understanding the spectral and timing behaviour of a newly discovered transient X-ray pulsar Swift J0243.6+6124

Understanding the spectral and timing behaviour of a newly discovered transient X-ray pulsar Swift J0243.6+6124

Dramatic spectral transition of X-ray pulsar GX 304−1 in low luminous state

Luminosity-dependent changes of the cyclotron line energy and spectral hardness in Cepheus X-4

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