Pulse Phase‐Resolved Analysis of the High‐Mass X‐Ray Binary Centaurus X‐3 over Two Binary Orbits

Abstract

We present a detailed analysis of observations of the high-mass X-ray binary Cen X-3, spanning two consecutive binary orbits performed with the RXTE satellite in early March 1997. During this time Cen X-3 had a luminosity of L 2Y10 keV $ (4Y5) ; 10 37 ergs s À1 and a pulse period of 4.814 s. The PCA and HEXTE light curves both show a clear reduction in count rate after midorbit for both binary revolutions. We therefore analyze two broadband spectra for each orbit, before and after midorbit. Consistent with earlier observations, these four joint PCA and HEXTE spectra can be well described using a phenomenological pulsar continuum model, including an iron emission line and a cyclotron resonance-scattering feature. While no strong spectral variations were detected, the second half of orbit 2 shows a tendency toward being softer and more strongly absorbed. In order to follow the orbital phase-dependent evolution of the spectrum in greater detail, we model spectra for shorter exposures, confirming that most spectral parameters show either a gradual or sudden change for the second half of the second orbit. A comparison with a simple wind model indicates the existence of an accretion wake in this system. We also present and discuss highresolution pulse profiles for several different energy bands, as well as their hardness ratios. PCA and HEXTE spectra were created for 24 phase bins and fitted using the same model as in the phase-averaged case. Systematic pulse phasedependent variations of several continuum and cyclotron line parameters were detected, most notably a significant increase of the cyclotron line energy during the early rise of the main peak, followed by a gradual decrease. We show that applying a simple dipole model for the magnetic field is not sufficient to describe our data.

Long term variability of Cygnus X-1

“…A second issue relates to the uncertainty of the N H measurements. For models such as the ones used here there is a wellknown degeneracy between the power law slope, i.e., Γ 1 , and N H (e.g., Suchy et al 2008). By calculating two-dimensional confidence contours we confirm that this degeneracy is not responsible for the variation of N H discussed here (for example contours see .…”

High-mass X-ray binaries in the Milky Way

“…It orbits an O6.5 II-III supergiant, located at 5-8 kpc (Day and Tennant, 1991;Krzeminski, 1974), in 2.1 days with a small eccentricity, if any (van der Meer et al, 2007;Falanga et al, 2015). Mass transfer probably occurs through a combination of wind and disk accretion (Petterson, 1978;Tsunemi et al, 1996;Tjemkes et al, 1986;Kohmura et al, 2001;Suchy et al, 2008). A cyclotron absorption feature is detected Santangelo et al, 1998;Heindl and Chakrabarty, 1999).…”

The Transient Accreting X-Ray Pulsar Xte J1946+274: Stability of X-Ray Properties at Low Flux and Updated Orbital Solution

“…This is a broad residual that has been observed in the spectra of several accreting pulsars thought to be caused by imperfect modeling of the continuum shape using empirical models (see, e.g., Coburn et al 2002). It is generally detected as a positive residual (e.g., in CenX-3, see Suchy et al 2008) but in some sources, including XTE J1946+274, it appears as a negative one (e.g., in VelaX-1, see Fürst et al 2014). We applied the deeper of the two detections reported for XTE J1946+274 by Müller et al (2012) to our model, i.e., following them, we included a gauabs component (another parameterization of the gabs shape) with E 9.85 keV, 10 keV = 2.2 keV, 10 keV s = and 0.069.…”