X-ray variability of the HMXB Cen X-3: evidence for inhomogeneous accretion flows

Abstract

Cen X-3 is a compact high mass X-ray binary likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of two pointed XMM-Newton observations. The first one took place during a normal state of the source, when it has a luminosity $L_{\mathrm{X}}\sim 10^{36}$ erg s${}^{-1}$. This observation covered orbital phases $\varphi =0.00-0.37$, i.e. the egress from the eclipse. The egress lightcurve is highly structured, showing distinctive intervals. We argue that different intervals correspond to the emergence of different emitting structures. The lightcurve analysis enables us to estimate the size of such structures around the compact star, the most conspicuous of which has a size $\sim 0.3R_{\ast }$, of the order of the Roche lobe radius. During the egress, the equivalent width of Fe emission lines, from highly ionized species, decreases as the X-ray continuum grows. On the other hand, the equivalent width of the Fe K$\alpha$ line, from near neutral Fe, strengthens. This line is likely formed due to the X-ray illumination of the accretion stream. The second observation was taken when the source was 10 times X-ray brighter and covered the orbital phases $\varphi =0.36-0.80$. The X-ray lightcurve in the high state shows dips. These dips are not caused by absorption but can be due to instabilities in the accretion stream. The typical dip duration, of about 1000~s, is much longer than the timescale attributed to the accretion of the clumpy stellar wind of the massive donor star, but is similar to the viscous timescale at the inner radius of the accretion disk.

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Cited by in corpus (12)

• The X-ray polarimetry view of the accreting pulsar Cen X-3
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• Detection of a quasi-periodic oscillation at $\sim$40 mHz in Cen X-3 with Insight-HXMT
• Detection of the orbital modulation of Fe K$\alpha$ fluorescence emission in Centaurus X-3 using the high-resolution spectrometer Resolve onboard XRISM
• Pulsating iron spectral features in the emission of X-ray pulsar V0332+53
• Orbital- and spin-phase variability in the X-ray emission from the accreting pulsar Cen X-3
• Timing and spectral studies of Cen X-3 in multiple luminosity states using $\text{AstroSat}$
• Revealing the state transition of Cen X-3 at high spectral resolution with Chandra
• Cen x-3 as seen by MAXI during six years
• XMM-Newton view of pulsating iron fluorescent emission from Centaurus X3
• The X-ray binaries in M83: will any of them form gravitational wave sources for LIGO/VIRGO/KAGRA?
• High-resolution X-ray spectroscopy of Cen X-3 with XMM-Newton