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Register a new userAn eccentric wave in the circumstellar disc of the Be/X-ray binary X Persei
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Added by
Radoslav K. Zamanov
Publication date
2019
fields
Physics
and research's language is
English
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We present spectroscopic observations of the Be/X-ray binary X Per obtained during the period December 2017 - January 2020 (MJD~58095 - MJD~58865). In December 2017 the $Halpha$, $Hbeta$, and HeI 6678 emission lines were symmetric with violet-to-red peak ratio $V/R approx 1$. During the first part of the period (December 2017 - August 2018) the V/R-ratio decreased to 0.5 and the asymmetry developed simultaneously in all three lines. In September 2018, a third component with velocity $approx 250$~km~s$^{-1}$ appeared on the red side of the HeI line profile. Later this component emerged in $Hbeta$, accompanied by the appearance of a red shoulder in $Halpha$. Assuming that it is due to an eccentric wave in the circumstellar disc, we find that the eccentric wave appeared first in the innermost part of the disc, it spreads out with outflowing velocity $v_{wave} approx 1.1 pm 0.2 $~km~s$^{-1}$, and the eccentricity of the eccentric wave is $e_{wave} approx 0.29 pm 0.07$. A detailed understanding of the origin of such eccentricities would have applications to a wide range of systems from planetary rings to AGNs.
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During normal Type I outbursts, the pulse profiles of Be/X-ray binary pulsars are found to be complex in soft X-ray energy ranges. The profiles in soft X-ray energy ranges are characterized by the presence of narrow absorption dips or dip-like features at several pulse phases. However, in hard X-ray energy ranges, the pulse profiles are rather smooth and single-peaked. Pulse phase-averaged spectroscopy of the these pulsars had been carried out during Type I outbursts. The broad-band spectrum of these pulsars were well described by partial covering high energy cutoff power-law model with interstellar absorption and Iron K_alpha emission line at 6.4 keV. Phase-resolved spectroscopy revealed that the presence of additional matter at certain pulse phases that partially obscured the emitted radiation giving rise to dips in the pulse profiles. The additional absorption is understood to be taking place by matter in the accretion streams that are phase locked with the neutron star. Optical/infrared observations of the companion Be star during these Type I outbursts showed that the increase in the X-ray intensity of the pulsar is coupled with the decrease in the optical/infrared flux of the companion star. There are also several changes in the IR/optical emission line profiles during these X-ray outbursts. The X-ray properties of these pulsars during Type I outbursts and corresponding changes in optical/infrared wavebands are discussed in this paper.
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