Spectral variability in Cygnus X-3

Hjalmarsdotter, L.; Zdziarski, A. A.; Szostek, A.; Hannikainen, D. C.

doi:10.1111/j.1365-2966.2008.14036.x

Cited by 53 publications

(123 citation statements)

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“…This source, also shown in Fig. 1, is found at 5.22 from 1FGL J1227.9-4852 and at 4.12 from the XSS J1227 optical 2 The broad-band 0.2-100 keV fluxes of LS I+61 • 303, LS 5039 and Cyg X-3 are taken from Chernyakova et al (2009), Takahashi et al (2009 and Hjalmarsdotter et al (2009), respectively. 3 http://www.heasarc.gsfc.nasa.gov/W3Browse/all/radio.…”

Section: Discussionmentioning

confidence: 66%

The intriguing nature of the high-energy gamma ray source XSS J12270-4859

Martino¹,

Falanga²,

Bonnet‐Bidaud

et al. 2010

A&A

100

125

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Context. The nature of the hard X-ray source XSS J12270-4859 is still unclear. It was claimed to be a possible magnetic cataclysmic variable of the Intermediate Polar type from its optical spectrum and a possible 860 s X-ray periodicity in RXTE data. However, recent observations do not support the latter variability, leaving this X-ray source still unclassified. Aims. To investigate its nature we present a broad-band X-ray and gamma ray study of this source based on a recent XMM-Newton observation and archival INTEGRAL and RXTE data. Using the Fermi/LAT 1-year point source catalogue, we tentatively associate XSS J12270-4859 with 1FGL J1227.9-4852, a source of high-energy gamma rays with emission up to 10 GeV. We further complement the study with UV photometry from XMM-Newton and ground-based optical and near-IR photometry. Methods. We have analysed both timing and spectral properties in the gamma rays, X-rays, UV and optical/near-IR bands of XSS J12270-4859. Results. The X-ray emission is highly variable, showing flares and intensity dips. The flares consist of flare-dip pairs. Flares are detected in both X-rays and the UV range, while the subsequent dips are present only in the X-ray band. Further aperiodic dipping behaviour is observed during X-ray quiescence, but not in the UV. The broad-band 0.2-100 keV X-ray/soft gamma ray spectrum is featureless and well described by a power law model with Γ = 1.7. The high-energy spectrum from 100 MeV to 10 GeV is represented by a power law index of 2.45. The luminosity ratio between 0.1-100 GeV and 0.2-100 keV is ∼0.8, indicating that the GeV emission is a significant component of the total energy output. Furthermore, the X-ray spectrum does not greatly change during flares, quiescence and the dips seen in quiescence. The X-ray spectrum however hardens during the post-flare dips, where a partial covering absorber is also required to fit the spectrum. Optical photometry acquired at different epochs reveals a period of 4.32 hr that could be ascribed to the binary orbital period. Near-IR, possibly ellipsoidal, variations are detected. Large amplitude variability on shorter (tens mins) timescales is found to be non-periodic. Conclusions. The observed variability at all wavelengths together with the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a magnetic cataclysmic variable nature. The association with a Fermi/LAT high-energy gamma ray source further strengths this interpretation.

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Section: Discussionmentioning

confidence: 66%

The intriguing nature of the high-energy gamma ray source XSS J12270-4859

Martino¹,

Falanga²,

Bonnet‐Bidaud

et al. 2010

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100

125

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“…From this analysis of the X-ray spectra of Cygnus X-3, Hjalmarsdotter et al (2009) infer that in the ultra-soft state, about half of the coronal power is provided to the electrons in the form of non-thermal electrons injected with a slope Γ inj 2.1. In principle, these non-thermal electrons could also be responsible for the gamma-ray emission detected by Fermi.…”

Section: Gamma-ray Emission From the Coronamentioning

confidence: 96%

“…In the EQPAIR model the grids used to compute the electron and photon energy distributions are fixed and cannot be extended to an energy high enough to simulate the Fermi emission. In Hjalmarsdotter et al (2009) the maximum Lorentz factor of the injected electrons is γ max = 10 3 , clearly too low to produce the gamma-ray emission. However, the exact value of γ max is not constrained by the X-ray data and could be much higher.…”

Section: Gamma-ray Emission From the Coronamentioning

confidence: 99%

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Absorption of high-energy gamma rays in Cygnus X-3

Cerutti

Dubus

Malzac

et al. 2011

A&A

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Context. The microquasar Cygnus X-3 was detected at high energies by the gamma-ray space telescopes AGILE and Fermi. The gamma-ray emission is transient, modulated with the orbital period and seems related to major radio flares, i.e. to the relativistic jet. The GeV gamma-ray flux can be substantially attenuated by internal absorption with the ambient X-rays. Aims. We examine quantitatively the effect of pair production in Cygnus X-3 and put constraints on the location of the gamma-ray source.Methods. Cygnus X-3 exhibits complex temporal and spectral patterns in X-rays. During gamma-ray flares, the X-ray emission can be approximated by a bright disk black-body component and a non-thermal tail extending in hard X-rays, which is possibly related to a corona above the disk. We calculate numerically the exact optical depth for gamma rays above a standard accretion disk. Emission and absorption in the corona are also investigated. Results. GeV gamma rays are significantly absorbed by soft X-rays emitted from the inner parts of the accretion disk. The absorption pattern is complex and anisotropic. Isotropization of X-rays caused by Thomson scattering in the companion-star wind tends to increase the gamma-ray opacity. Gamma rays from the corona suffer from strong absorption by photons from the disk and cannot explain the observed high-energy emission, unless the corona is unrealistically extended. Conclusions. The lack of an absorption feature in the GeV emission indicates that high-energy gamma rays should be located at a minimum distance ∼10 8 −10 10 cm from the compact object. The gamma-ray emission is unlikely to have a coronal origin.

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“…However, if the mass of the black hole is small, then its disc is hot, keeping it out of the ultrasoft domain populated by more massive black holes. On the other hand, based on spectral evolution vs. the Eddington luminosity, Hjalmarsdotter et al (2008b) point to a massive (30 M ) black hole, and consequently a very small inclination, with a massive WR companion.…”

Section: Light Curves Of the Emission And Absorption Componentsmentioning

confidence: 97%

Orbital modulation of X-ray emission lines in Cygnus X-3

Vilhu

Hakala

Hannikainen

et al. 2009

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Aims. We address the problem where the X-ray emission lines are formed and investigate orbital dynamics using Chandra HETG observations, photoionizing calculations and numerical wind-particle simulations. The aims were to set constraints on the masses of the components of this close binary system consisting of a Wolf-Rayet (WR) star and a compact component and to investigate the nature of the latter (neutron star or black hole). The goal was also to investigate P Cygni signatures in line profiles.Methods. The observed Si xiv (6.185 Å) and S xvi (4.733 Å) line profiles at four orbital phases were fitted with P Cygni-type profiles consisting of an emission and a blue-shifted absorption component. Numerical models were constructed using photoionizing calculations and particle simulations. In the models, the emission originates in the photoionized wind of the WR companion illuminated by a hybrid source: the X-ray radiation of the compact star and the photospheric EUV-radiation from the WR star.Results. Spectral lines with moderate excitation (such as Si xiv and S xvi) arise in the photoionized wind. The emission component exhibits maximum blue-shift at phase 0.5 (when the compact star is in front), while the velocity of the absorption component is constant (around −900 km s −1 ). Both components, like the continuum flux, have intensity maxima around phase 0.5. The simulated Fe xxvi Lyα line (1.78 Å, H-like) from the wind is weak compared to the observed one. We suggest that it originates in the vicinity of the compact star, with a maximum blue shift at phase 0.25 (compact star approaching). By combining the mass function derived with that from the infrared He i absorption (arising from the WR companion), we constrain the masses and the inclination of the system. Conclusions. The Si xiv and S xvi lines and their radial velocity curves can be understood in the framework of a photoionized wind involving a hybrid ionizer. Constraints on the compact star mass and orbital inclination (i) are given using the mass functions derived from the Fe xxvi line and He i 2.06 μm absorption. Both a neutron star at large inclination (i ≥ 60 degrees) and a black hole at small inclination are possible solutions. The radial velocity amplitude of the He ii 2.09 μm emission (formed in the X-ray shadow behind the WR star) suggests i = 30 degrees, implying a possible compact star mass between 2.8-8.0 M . For i = 60 degrees the same range is 1.0-3.2 M .

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Spectral variability in Cygnus X-3

Cited by 53 publications

References 40 publications

The intriguing nature of the high-energy gamma ray source XSS J12270-4859

The intriguing nature of the high-energy gamma ray source XSS J12270-4859

Absorption of high-energy gamma rays in Cygnus X-3

Orbital modulation of X-ray emission lines in Cygnus X-3

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