Proceedings of the Xxiii International; Cosmic Ray Conference

Leahy, D. A.; Hicks, R. B.; Venkatesan, D.

doi:10.1142/9789814535304

Cited by 12 publications

(14 citation statements)

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“…The Alfvén surface is currently the most popular one. However, also the accretion column was proposed (e.g., Leahy 2001 andİnam &Baykal 2005), despite the argument by White et al (1983) that the material in the column may be too hot.…”

Section: Comparison With Previous Results and Physical Conclusionmentioning

confidence: 99%

Pulse phase and precession phase resolved spectroscopy of Hercules X-1: studying a representative Main-On with RXTE

Vasco

Staubert

Klochkov

et al. 2013

A&A

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Aims. We performed a detailed pulse phase resolved spectroscopy of the accreting binary X-ray pulsar Her X-1 in the energy range 3.5-75 keV and have established pulse phase profiles for all spectral parameters. For three parameters, the centroid energy of the cyclotron line, the photon index and the flux of the 6.4 keV iron line, we have studied the variation as a function of 35 d phase. Methods. We analyzed RXTE observations of the Main-On of November 2002 using data from the PCA and the HEXTE instruments. Four different time intervals of about ∼1 d duration were selected to provide a good coverage of a complete Main-On. The intervals are centered at 35 d phases 0.03, 0.10, 0.15, and 0.20, respectively. Results. All spectral parameters show a strong modulation with pulse phase. While the centroid energy of the cyclotron line follows roughly the shape of the pulse profile, showing higher values close to the peak of the X-ray pulse, both the photon index and the iron line intensity exhibit distinct minima around the peak of the X-ray pulse. With respect to variations of the observed profiles with 35 d phase, we find that there is a clear evolution of the shape of the pulse profiles (flux versus pulse phase), a moderate increase of the maximum cyclotron line energy (found around pulse phase 0.7), but no significant evolution of the shape of the pulse phase profiles of the cyclotron line energy, the spectral power law index or the iron line intensity. Conclusions. The variation of spectral parameters as a function of the pulse phase provides important information about the system: i. the disappearance of the Fe line flux near the highest continuum flux may be an indication of a hollow cone geometry of the accretion structure; ii. the apparent non-dependence of the cyclotron line energy profiles on 35 d phase provides a new possibility to test the model of free precession of the neutron star, proposed to be responsible for the systematic variations in the pulse profiles.

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Section: Comparison With Previous Results and Physical Conclusionmentioning

confidence: 99%

Pulse phase and precession phase resolved spectroscopy of Hercules X-1: studying a representative Main-On with RXTE

Vasco

Staubert

Klochkov

et al. 2013

A&A

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“…For 4U 1907+09, n H increases to its maximum value after the periastron passage, which implies that the location of the absorbing material is the dense stellar wind of the companion star (Roberts et al 2001). Leahy (2001) and Kostka & Leahy (2010) have modelled the absorption profile according to theoretical wind models. They have proposed that the most probable mechanism for 4U 1907+09 is accretion from a spherical wind with an equatorially enhanced dense spiral stream of gas around the companion star.…”

Section: Spectral Analysismentioning

confidence: 99%

A comprehensive study of RXTE and INTEGRAL observations of the X-ray pulsar 4U 1907+09

Şahiner¹,

İnam²,

Baykal³

2012

Monthly Notices of the Royal Astronomical Society

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We analyse observations of the accretion‐powered pulsar 4U 1907+09 from the International Gamma‐Ray Astrophysics Laboratory (INTEGRAL; between 2005 October and 2007 November) and from the Rossi X‐ray Timing Explorer (RXTE; between 2007 June and 2011 March). Using observations from the Imager on‐board the INTEGRAL satellite (IBIS), the INTEGRAL Soft Gamma‐Ray Imager (ISGRI) and the RXTE Proportional Counter Array (PCA), we update the pulse period history of the source. We construct power spectrum density of pulse frequencies, and we find that fluctuations in the pulse frequency derivatives are consistent with the random walk model with a noise strength of 1.27 × 10−21 Hz s−2. From the X‐ray spectral analysis of RXTE/PCA observations, we find that the hydrogen column density is variable over the binary orbit, and that it tends to increase just after the periastron passage. We also show that the X‐ray spectrum becomes hardened with decreasing X‐ray flux. We discuss the pulse‐to‐pulse variability of the source near dipping ingress and egress. We find that the source is more likely to undergo dipping states after apastron until periastron when the accretion from clumpy wind might dominate. Thus, occasional transitions to a temporary propeller state might occur.

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“…Using a Bayesian analysis of 20 years of radio data, Gregory (2002) determined the orbital period P 1 = 26.4960 ± 0.0028 d. The compact object moving around the Be star and interacting with circumstellar matter produces the orbital variability seen in all parts of the spectrum (Taylor et al 1992;Mendelson & Mazeh 1989;Leahy 2001;Grundstrom et al 2007). A Lomb-Scargle timing analysis of 37 years of radio data resulted in the detection of the second period, P 2 = 26.935 ± 0.013 d (Massi & Torricelli-Ciamponi 2016), which is consistent with a previously determined period of morphological changes in the radio structure, mapped in the VLBI images (Massi et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Orbital variability of the optical linear polarization of the γ-ray binary LS I +61° 303 and new constraints on the orbital parameters

Kravtsov

Berdyugin²,

Piirola³

et al. 2020

A&A

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We studied the variability of the linear polarization and brightness of the γ-ray binary LS I +61° 303. High-precision BVR photopolarimetric observations were carried out with the Dipol-2 polarimeter on the 2.2 m remotely controlled UH88 telescope at Mauna Kea Observatory and the 60 cm Tohoku telescope at Haleakala bservatory (Hawaii) over 140 nights in 2016−2019. We also determined the degree and angle of the interstellar polarization toward LS I +61° 303 using two out of four nearby field stars that have Gaia’s parallaxes. After subtracting the interstellar polarization, we determined the position angle of the intrinsic polarization θ ≃ 11°, which can either be associated with the projection of the Be star’s decretion disk axis on the plane of sky, or can differ from it by 90°. Using the Lomb-Scargle method, we performed timing analyses and period searches of our polarimetric and photometric data. We found statistically significant periodic variability of the normalized Stokes parameters q and u in all passbands. The most significant period of variability, PPol = 13.244 ± 0.012 d, is equal to one half of the orbital period Porb = 26.496 d. The fits of the polarization variability curves with Fourier series show a dominant contribution from the second harmonic which is typical for binary systems with circular orbits and nearly symmetric distribution of light scattering material with respect to the orbital plane. The continuous change of polarization with the orbital phase implies co-planarity of the orbit of the compact object and the Be star’s decretion disk. Using a model of Thomson scattering by a cloud that orbits the Be star, we obtained constraints on the orbital parameters, including a small eccentricity e < 0.2 and periastron phase of ϕp ≈ 0.6, which coincides with the peaks in the radio, X-ray, and TeV emission. These constraints are independent of the assumption about the orientation of the decretion disk plane on the sky. We also extensively discuss the apparent inconsistency with the previous measurements of the orbital parameters from radial velocities. By folding the photometry data acquired during a three-year time span with the orbital period, we found a linear phase shift of the moments of the brightness maximum, confirming the possible existence of superorbital variability.

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Proceedings of the Xxiii International; Cosmic Ray Conference

Cited by 12 publications

References 0 publications

Pulse phase and precession phase resolved spectroscopy of Hercules X-1: studying a representative Main-On with RXTE

Pulse phase and precession phase resolved spectroscopy of Hercules X-1: studying a representative Main-On with RXTE

A comprehensive study of RXTE and INTEGRAL observations of the X-ray pulsar 4U 1907+09

Orbital variability of the optical linear polarization of the γ-ray binary LS I +61° 303 and new constraints on the orbital parameters

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