Recent timing studies on RXTE observations of 4U 1538-52

Baykal, A.; İnam, S. Ç.; Beklen, E.

doi:10.1051/0004-6361:20054616

Cited by 20 publications

(24 citation statements)

References 15 publications

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“…Pulse period evolution of 4U 1538−522. Binary-corrected periods found in this work are represented by red asterisks, with previous measurements (Becker et al 1977;Makishima et al 1987;Corbet et al 1993;Rubin et al 1997;Clark 2000;Baykal et al 2006) and recent Fermi GBM data (Finger et al 2009 Table 3 and the source's pulse period history is updated in Figure 2. Pulse periods from the earlier data, prior to 2008, follow roughly the same spin-up trend as originally seen by Rubin et al (1997), with the period dropping at a rate of ∼0.2 s yr −1 .…”

Section: U 1538−522supporting

confidence: 72%

MEASUREMENTS OF CYCLOTRON FEATURES AND PULSE PERIODS IN THE HIGH-MASS X-RAY BINARIES 4U 1538–522 AND 4U 1907+09 WITH THEINTERNATIONAL GAMMA-RAY ASTROPHYSICS LABORATORY

Hemphill

Rothschild

Caballero

et al. 2013

ApJ

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We present a spectral and timing analysis of International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of two high-mass X-ray binaries, 4U 1538−522 and 4U 1907+09. Our timing measurements for 4U 1538−522 find the pulse period to have exhibited a spin-up trend until approximately 2009, after which there is evidence for a torque reversal, with the source beginning to spin down to the most recently measured period of 525.407 ± 0.001 s. The most recent INTEGRAL observations of 4U 1907+09 are not found to yield statistically significant pulse periods due to the significantly lower flux from the source compared with 4U 1538−522. A spectral model consisting of a power-law continuum with an exponential cutoff and modified by two cyclotron resonance scattering features is found to fit both sources well, with the cyclotron scattering features detected at ∼22 and ∼49 keV for 4U 1538−522 and at ∼18 and ∼36 keV for 4U 1907+09. The spectral parameters of 4U 1538−522 are generally not found to vary significantly with flux and there is little to no variation across the torque reversal. Examining our results in conjunction with previous work, we find no evidence for a correlation between cyclotron line energy and luminosity for 4U 1538−522. 4U 1907+09 shows evidence for a positive correlation between cyclotron line energy and luminosity, which would make it the fourth, and lowest luminosity, cyclotron line source to exhibit this relationship.

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Section: U 1538−522supporting

confidence: 72%

MEASUREMENTS OF CYCLOTRON FEATURES AND PULSE PERIODS IN THE HIGH-MASS X-RAY BINARIES 4U 1538–522 AND 4U 1907+09 WITH THEINTERNATIONAL GAMMA-RAY ASTROPHYSICS LABORATORY

Hemphill

Rothschild

Caballero

et al. 2013

ApJ

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“…Then we folded the light curves with the best orbital period to obtain energy-resolved orbital intensity profiles. The orbital phase reference is taken from Mukherjee et al (2006) (see also Baykal et al 2006), with the phase zero corresponding to mideclipse in Fig. 1.…”

Section: Timing Analysismentioning

confidence: 99%

Orbital phase-resolved spectroscopy of 4U 1538−52 with MAXI

Roca

Mihara

Nakahira

et al. 2015

A&A

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Context. 4U 1538−52, an absorbed high mass X-ray binary with an orbital period of ∼3.73 days, shows moderate orbital intensity modulations with a low level of counts during the eclipse. Several models have been proposed to explain the accretion at different orbital phases by a spherically symmetric stellar wind from the companion. Aims. The aim of this work is to study both the light curve and orbital phase spectroscopy of this source in the long term. In particular, we study the folded light curve and the changes in the spectral parameters with orbital phase to analyse the stellar wind of QV Nor, the mass donor of this binary system. Methods. We used all the observations made from the Gas Slit Camera on board MAXI of 4U 1538−52 covering many orbits continuously. We obtained the good interval times for all orbital phase ranges, which were the input for extracting our data. We estimated the orbital period of the system and then folded the light curves, and we fitted the X-ray spectra with the same model for every orbital phase spectrum. We also extracted the averaged spectrum of all the MAXI data available. Results. The MAXI spectra in the 2-20 keV energy range were fitted with an absorbed Comptonisation of cool photons on hot electrons. We found a strong orbital dependence of the absorption column density but neither the fluorescence iron emission line nor low energy excess were needed to fit the MAXI spectra. The variation in the spectral parameters over the binary orbit were used to examine the mode of accretion onto the neutron star in 4U 1538−52. We deduce a best value ofṀ/v ∞ = 0.65 × 10 −9 M yr −1 /(km s −1 ) for QV Nor.

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“…(2) The NS orbits QV Nor in a 3.7 d orbit at radial distances from the donor star, ranging from r R 1.35 * to R 1.5 ⪅ * , allowing probing of the innermost wind region of a B0I star. Two orbital solutions are possible (Clark 2000;Baykal et al 2006;Mukherjee et al 2006) and both can individually be precisely determined. (3) The periastron passage is very close to the eclipse, allowing probing of the innermost wind with a maximum contrast between the emission lines and the continuum.…”

Section: Introductionmentioning

confidence: 99%

On the Radial Onset of Clumping in the Wind of the B0i Massive Star Qv Nor

Torrejón

Schulz

Nowak

et al. 2015

ApJ

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We present an analysis of a 78 ks Chandra high-energy transmission gratings observation of the B0I star QV Nor, the massive donor of the wind-accreting pulsar 4U1538−52. The neutron star (NS) orbits its companion in a very close orbit (r R 1.4 * < , in units of the stellar radii), thereby allowing probing of the innermost wind regions. The flux of the Fe Kα line during eclipse reduces to only ∼30% of the flux measured out of eclipse. This indicates that the majority of Fe fluorescence must be produced in regions close to the NS, at distances smaller than R 1 * from its surface. The fact that the flux of the continuum decreases to only ∼3% during eclipse allows for a high contrast of the Fe Kα line fluorescence during eclipse. The line is not resolved and centered at 1.9368 0.0018 0.0032 l =-+ Å. From the inferred plasma speed limit of v c 800 < < l l D km s −1 and range of ionization parameters of log 1, 2 [ ] x =-, together with the stellar density profile, we constrain the location of the cold, dense material in the stellar wind of QV Nor using simple geometrical considerations. We then use the Fe Kα line fluorescence as a tracer of wind clumps and determine that these clumps in the stellar wind of QV Nor (B0I) must already be present at radii r R 1.25 * < , close to the photosphere of the star.

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Recent timing studies on RXTE observations of 4U 1538-52

Cited by 20 publications

References 15 publications

MEASUREMENTS OF CYCLOTRON FEATURES AND PULSE PERIODS IN THE HIGH-MASS X-RAY BINARIES 4U 1538–522 AND 4U 1907+09 WITH THEINTERNATIONAL GAMMA-RAY ASTROPHYSICS LABORATORY

MEASUREMENTS OF CYCLOTRON FEATURES AND PULSE PERIODS IN THE HIGH-MASS X-RAY BINARIES 4U 1538–522 AND 4U 1907+09 WITH THEINTERNATIONAL GAMMA-RAY ASTROPHYSICS LABORATORY

Orbital phase-resolved spectroscopy of 4U 1538−52 with MAXI

On the Radial Onset of Clumping in the Wind of the B0i Massive Star Qv Nor

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