Thermal and Bulk Comptonization in Accretion‐powered X‐Ray Pulsars

Becker, Peter A.; Wolff, M. T.

doi:10.1086/509108

Cited by 283 publications

(387 citation statements)

References 47 publications

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“…The spectral analysis is performed with the Xspec package version 12.3.1 (Arnaud 1996), using our implementation of the analytical model for the vertically-integrated accretion column emission spectrum developed by Becker & Wolff (2007). The fundamental and harmonic cyclotron resonant absorption features are modeled using multiplicative Gaussian functions:…”

Section: Spectral Analysismentioning

confidence: 99%

“…After providing a brief summary of the Becker & Wolff (2007) column emission model, in Sect. 3 we describe the observations and the analysis methods.…”

Section: Introductionmentioning

confidence: 99%

“…6, we draw our conclusions. Becker & Wolff (2007) proposed a model for the production of the accretion column emission spectrum based on the bulk and thermal Comptonization of seed photons emitted via bremsstrahlung, cyclotron, and blackbody processes occurring in the accreting plasma. The partial differential equation governing the Green's function yields an analytical solution that can be convolved with the seed photon distribution to produce an emergent spectrum displaying a power-law continuum with an exponential cutoff at high energies.…”

Section: Introductionmentioning

confidence: 99%

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Study of the accreting pulsar 4U 0115+63 using a bulk and thermal Comptonization model

Ferrigno

Becker

Segreto

et al. 2009

A&A

127

148

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Context. Highly magnetized pulsars accreting matter in a binary system are bright sources in the X-ray band (0.1-100 keV). Despite the early comprehension of the basic emission mechanism, their spectral energy distribution is generally described by phenomenological or simplified models. Aims. We propose a study of the spectral emission from the high mass X-ray binary pulsar 4U 0115+63 by means of thermal and bulk Comptonization models based on the physical properties of such objects. Methods.For this purpose, we analyze the BeppoSAX data in the energy range 0.7-100 keV of the 1999 giant outburst, 12 days after the maximum. We focus first on the phase averaged emission, and then on the phase resolved spectra, by modeling the system using a two-component continuum. Results. At higher energy, above ∼7 keV, the emission is due to thermal and bulk Comptonization of the seed photons produced by cyclotron cooling of the accretion column, and at lower energy, the emission is due to thermal Comptonization of a blackbody source in a diffuse halo close to the stellar surface. Phase resolved analysis establishes that most of the emission in the main peak comes from the column, while the low energy component gives a nearly constant contribution throughout the phase. Conclusions. From the best fit parameters, we argue that the cyclotron emission is produced ∼1.7 km above the stellar surface, and escapes from the column near its base, where the absorption features are generated by the interaction with the magnetic field in the halo. We find that in 4U 0115+63, the observed spectrum is dominated by reprocessed cyclotron radiation, whereas in other bright sources with stronger magnetic fields such as Her X-1, the spectrum is dominated by reprocessed bremsstrahlung.

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Section: Spectral Analysismentioning

confidence: 99%

“…After providing a brief summary of the Becker & Wolff (2007) column emission model, in Sect. 3 we describe the observations and the analysis methods.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of the accreting pulsar 4U 0115+63 using a bulk and thermal Comptonization model

Ferrigno

Becker

Segreto

et al. 2009

A&A

127

148

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show abstract

“…Basko and Sunyaev, 1976;Nagel, 1981;Meszaros and Nagel, 1985;Araya-Góchez and Harding, 2000;Nishimura, 2008;Mushtukov et al, 2015). Bulk and thermal Comptonization plays a key role in the formation of the non thermal X-ray emission (Becker and Wolff, 2007).…”

Section: Introductionmentioning

confidence: 99%

High-mass X-ray binaries in the Milky Way

Walter

Lutovinov

Bozzo

et al. 2015

Astron Astrophys Rev

234

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High-mass X-ray binaries are fundamental in the study of stellar evolution, nucleosynthesis, structure and evolution of galaxies and accretion processes. Hard X-rays observations by INTEGRAL and Swift have broadened significantly our understanding in particular for the super-giant systems in the Milky Way, which number has increased by almost a factor of three. INTEGRAL played a crucial role in the discovery, study and understanding of heavily obscured systems and of fast X-ray transients. Most super-giant systems can now be classified in three categories: classical/obscured, eccentric and fast transient.The classical systems feature low eccentricity and variability factor of ∼ 10 3 , mostly driven by hydrodynamic phenomena occurring on scales larger than the accretion radius. Among them, systems with short orbital periods and close to Roche-Lobe overflow or with slow winds, appear highly obscured. In eccentric systems, the variability amplitude can reach even higher factors, because of the contrast of the wind density along the orbit. Four super-giant systems, featuring fast outbursts, very short orbital periods and anomalously low accretion rates, are not yet understood.Simulations of the accretion processes on relatively large scales have progressed and reproduce parts of the observations. The combined effects of wind

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“…The continuum is believed to be due to thermal bremsstrahlung radiation from the ∼10 8 K hot plasma modified by Comptonization (Becker & Wolff 2007;Becker et al 2012). The line feature was discovered in 1976 in a balloon observation (Trümper et al 1978).…”

Section: Introductionmentioning

confidence: 99%

Long-term change in the cyclotron line energy in Hercules X-1

Staubert

Klochkov

Wilms³

et al. 2014

A&A

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Aims. We investigate the long-term evolution of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1 and present evidence of a true long-term decrease in the centroid energy E cyc of the cyclotron line in the pulse phase averaged spectra from 1996 to 2012. Methods. Our results are based on repeated observations of Her X-1 by those X-ray observatories capable of measuring clearly beyond the cyclotron line energy of ∼ 40 keV. Results. The historical evolution of the pulse phase averaged CRSF centroid energy E cyc since its discovery in 1976 is characterized by an initial value around 35 keV, an abrupt jump upwards to beyond ∼ 40 keV between 1990 and 1994, and an apparent decay thereafter. Much of this decay, however, was found to be due to an artifact, namely a correlation between E cyc and the X-ray luminosity L x discovered in 2007. In observations after 2006, however, we now find a statistically significant true decrease in the cyclotron line energy. At the same time, the dependence of E cyc on X-ray luminosity is still valid with an increase of ∼ 5% in energy for a factor of two increase in luminosity. A decrease in E cyc by 4.2 keV over the 16 years from 1996 to 2012 can either be modeled by a linear decay, or by a slow decay until 2006 followed by a more abrupt decrease thereafter. Conclusions. We speculate that the physical reason could be connected to a geometric displacement of the cyclotron resonant scattering region in the polar field or to a true physical change in the magnetic field configuration at the polar cap by the continued accretion.

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Thermal and Bulk Comptonization in Accretion‐powered X‐Ray Pulsars

Cited by 283 publications

References 47 publications

Study of the accreting pulsar 4U 0115+63 using a bulk and thermal Comptonization model

Study of the accreting pulsar 4U 0115+63 using a bulk and thermal Comptonization model

High-mass X-ray binaries in the Milky Way

Long-term change in the cyclotron line energy in Hercules X-1

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