X-Ray Spectroscopy of the High-Mass X-Ray Binary Pulsar Centaurus X-3 Over Its Binary Orbit

Abstract

We present a comprehensive spectral analysis of the high-mass X-ray binary (HMXB) pulsar Centaurus X-3 with the Suzaku observatory covering nearly one orbital period. The light curve shows the presence of extended dips which are rarely seen in HMXBs. These dips are seen up to as high as ∼40 keV. The pulsar spectra during the eclipse, out-of-eclipse, and dips are found to be well described by a partial covering power-law model with high-energy cutoff and three Gaussian functions for 6.4 keV, 6.7 keV, and 6.97 keV iron emission lines. The dips in the light curve can be explained by the presence of an additional absorption component with high column density and covering fraction, the values of which are not significant during the rest of the orbital phases. The iron line parameters during the dips and eclipse are significantly different compared to those during the rest of the observation. During the dips, the iron line intensities are found to be lesser by a factor of 2-3 with a significant increase in the line equivalent widths. However, the continuum flux at the corresponding orbital phase is estimated to be lesser by more than an order of magnitude. Similarities in the changes in the iron line flux and equivalent widths during the dips and eclipse segments suggest that the dipping activity in Cen X-3 is caused by an obscuration of the neutron star by dense matter, probably structures in the outer region of the accretion disk, as in the case of dipping low-mass X-ray binaries.

X-Ray Reprocessing: Through the Eclipse Spectra of High-mass X-Ray Binaries with XMM-Newton

“…A cyclotron resonance scattering feature at 28 keV and 30 keV has been detected in Cen X-3 with two BeppoSAX observations (Santangelo et al 1998;Burderi et al 2000). Suzaku observation of Cen X-3 covering a full binary orbit showed multiple extended dips with spectral characteristics similar to that of the source in eclipse, indicating the dips to be produced due to obscuration by dense matter which are structures in the outer region of the accretion disk (Naik, Paul & Ali 2011) LMC X-4 is a wind and disk fed persistent system in the Large Magellanic Cloud (LMC) which often shows X-ray flares sometimes with super Eddington luminosity (Levine, Rappaport & Zojcheski 2000;Moon, Eikenberry & Wasserman 2003). The source was found to show pe- (Bildsten et al 1997), a6 (Raichur & Paul 2010), a7 (Thompson & Rothschild 2009), b2 (Li, Rappaport & Epstein 1978); (White 1978), b3 (Levine, Rappaport & Zojcheski 2000), b4 (Pietrzyński et al 2013), c2 (Schreier et al 1972a), c3 (Val Baker, Norton & Quaintrell 2005, c4 (Primini, Rappaport & Joss 1977), c5 (Reynolds et al 1993), c6 (Levine et al 1993), c7 (Hilditch, Howarth & Harries 2005) d1 (Jones et al 1973), d2 (Clark et al 2002), d3 (Penny et al 1973), d4 , d5 (Ankay et al 2001) e2 (Becker et al 1977), e3 (Reynolds, Bell & Hilditch 1992), e4 (Parkes, Murdin & Mason 1978), (Falanga et al 2015), e5 (Mukherjee et al 2006 (Sguera et al 2005), g1 (Molkov et al 2003), g2 (Jain, Paul & Dutta 2009a), g3 (Vacca, Garmany & Shull 1996), g4 (Nespoli, Fabregat & Mennickent 2008), h0 (Romano et al 2011), h2 <...>…”

A new model for the X-ray continuum of the magnetized accreting pulsars

“…Observations performed with the gratings on board Chandra also show the presence of Doppler broadened Si xiii, Si xiv, and Fe xxv complexes caused by recombination in a photoionized plasma (Wojdowski et al 2003;Iaria et al 2005). It has been argued that the fluorescent lines originate relatively close to the NS (probably in the outer regions of the accretion disk), while the other lines are produced at greater distances from the NS in the wind of the massive companion (Iaria et al 2005;Naik et al 2011). The stellar wind velocity measured from these lines is significantly smaller than that expected for an O-type star, providing convincing indications for a strong perturbation of the wind by the NS X-ray radiation.…”

“…The spectral energy distribution also shows a remarkable dependence on the spin and orbital phase (see e.g. Suchy et al 2008;Raichur & Paul 2008;Naik et al 2011, and references therein).…”

Glancing through the accretion column of EXO 2030+375

“…Depending on the statistics of the data and the energy coverage, it proved necessary in several cases to complement these relatively simple spectral models with the additions of broad Gaussian components (see, e.g., Klochkov et al 2007;Suchy et al 2008) and/or partial covering absorbers (Naik et al 2011(Naik et al , 2013Naik & Jaisawal 2015). Furthermore, the cyclotron resonant scattering of electrons in the high magnetic field of the NS is known to produce characteristic absorption lines that have been observed in several of these systems and included in the spectral fits by using either Gaussian or Lorentzian profiles (see, e.g., Walter et al 2015, for a recent review).…”