Fast time optical variability in Be/X-ray binaries

Reig, P.; Fabregat, J.

doi:10.1051/0004-6361/202243664

Cited by 6 publications

(4 citation statements)

References 199 publications

(264 reference statements)

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“…Our study of KS 1947+300 emphasizes the variable nature of BeXBs in the optical band on all time scales: long (years) as shown in Sect. 3.1, intermediate (weeks to months) as shown in this section, and short (hours to days) as shown by Reig & Fabregat (2022).…”

Section: Periodic Signals In Ztf-g and R Band Light Curvessupporting

confidence: 56%

“…Kızıloglu et al (2007) performed optical photometry of KS 1947+300 with high cadence and found an increase of about 0.1 mag in coincidence with and increase in the X-ray flux from quiescence to 5 × 10 36 erg s −1 , typical behavior of a type I outburst. Other works that report optical observations of KS 1947+300 in the context of a global study of the optical properties of BeXBs are given in Reig & Fabregat (2015), Reig et al (2016), and Reig & Fabregat (2022).…”

Section: Introductionmentioning

confidence: 99%

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Multiwavelength observations of KS 1947+300

Liu,

Reig,

Yan

et al. 2023

Preprint

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Context. KS 1947+300 is a Be/X-ray binary. Despite its nearly circular orbit, it displays both giant and regular less intense X-ray outbursts. According to the viscous decretion disk model, such low eccentric binaries should not show periodic outbursts. Aims. We have studied the long-term optical variability of KS 1947+300 and its relationship with X-ray activity. Our objective is to investigate the origin of this variability. Methods. We have analyzed data covering more than 20 years of observations. In the optical band, we have analyzed spectra and light curves. We measured the strength of the Hα and He I 6678 Å lines. In the X-ray band, we studied the long-term light curves provided by several all-sky monitors. Results. KS 1947+300 exhibits changes in brightness and Hα emission on time scales from months to years. The optical and IR variability shows small amplitude changes during the active X-ray state, and a long, smooth decrease during the quiescent state. The fact that the amplitude of variability increased with wavelength suggests that the long-term decrease of the optical emission is due to the weakening of the circumstellar disk. Structural changes in the disk may also be the origin of the periodic signals with periods ∼ 200 days detected in the ZTF-g and r band light curves. We speculate that these changes are related to the mechanism that ejects matter from the photosphere of the Be star into the disk. We have also studied the X-ray variability that manifested as a series of type I outbursts after the two giant outburst in 2000 and 2013 and found that the intensity and peak orbital phase differ from outburst to outburst. The type I outbursts in KS 1947+300 are not strictly periodic. This irregularity could result from precession of the interacting points between the neutron star and the disk, namely the disk apastron and the two nodes of the disk. Conclusions. The long-term changes in optical continuum and line emission and the X-ray variability patterns are attributed to an evolving and distorted decretion disk.

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Section: Periodic Signals In Ztf-g and R Band Light Curvessupporting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Multiwavelength observations of KS 1947+300

Liu,

Reig,

Yan

et al. 2023

Preprint

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“…The massive companion is a long-term variable system with photometric and spectroscopic changes on timescales of years (Kızıloǧlu et al 2007;Reig & Fabregat 2015;Reig et al 2016). The underlying B star also displays fast optical multiperiodic variability that is attributed to nonradial pulsations (Kızıloǧlu et al 2007;Reig & Fabregat 2022). We present the most complete and detailed study of the optical variability of the BeXB GRO J2058+42 performed so far.…”

Section: Introductionmentioning

confidence: 96%

Long-term optical variability of the Be/X-ray binary GRO J2058+42

Reig

Tzouvanou

Blinov

et al. 2023

A&A

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Context. GRO J2058+42 is a transient hard X-ray pulsar that occasionally goes into outburst. The optical counterpart is a poorly studied OB-type companion. Aims. We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. Methods. We performed an optical spectroscopic and photometric analysis on data collected during about 18 yr. We also present the first optical polarimetric observations of this source. Results. The long-term optical light curves in the BVRI bands and the evolution of the Hα equivalent width display a sinusoidal pattern with maxima and minima that repeat every ∼9.5 yr. The amplitude of this variability increases as the wavelength increases from 0.3 mag in the B band to 0.7 in the I band. The Hα equivalent width varied from about −0.3 to −15 Å. We found a significant decrease in the polarization degree during the low optical state. The intrinsic polarization degree changed by ∼1% from maximum to minimum. The optical maxima occur near periods of enhanced X-ray activity and are followed by a drop in the optical emission. Unlike many other Be/X-ray binaries, GRO J2058+42 does not display V/R variability. Conclusions. The long-term optical variability agrees with the standard model of a Be/X-ray binary, where the circumstellar disk of the Be star grows and dissipates on timescales of 9−10 yr. We find that the dissipation of the disk started after a major X-ray outburst. However, the stability of the Hα line shape as a double-peak profile and the lack of asymmetries suggest the absence of a warped disk and argue against the presence of a highly distorted disk during major X-ray outbursts.

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Section: Introductionmentioning

confidence: 99%

Long-term optical variability of the Be/X-ray binary GRO J2058+42

Reig¹,

Tzouvano²,

Blinov³

et al. 2023

Preprint

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Context. GRO J2058+42 is a transient hard X-ray pulsar that occasionally goes into outburst. The optical counterpart is a poorly studied OB-type companion. Aims. We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. Methods. We performed an optical spectroscopic and photometric analysis on data collected during about 18 years. We also present the first optical polarimetric observations of this source.Results. The long-term optical light curves in the BVRI bands and the evolution of the Hα equivalent width display a sinusoidal pattern with maxima and minima that repeat every ∼9.5 years. The amplitude of this variability increases as the wavelength increases from 0.3 mag in the B band to 0.8 in the I band. The Hα equivalent width varied from about −0.3 to −15 Å. We found a significant decrease in the polarization degree during the low optical state. The intrinsic polarization degree changed by ∼ 1% from maximum to minimum. The optical maxima occur near periods of enhanced X-ray activity and are followed by a drop in the optical emission. Unlike many other Be/X-ray binaries, GRO J2058+42 does not display V/R variability. Conclusions. The long-term optical variability agrees with the standard model of a Be/X-ray binary, where the circumstellar disk of the Be star grows and dissipates on timescales of 9-10 years. We find that the dissipation of the disk started after a major X-ray outburst. However, the stability of the Hα line shape as a double-peak profile and the lack of asymmetries suggest the absence of a warped disk and argue against the presence of a highly distorted disk during major X-ray outbursts.

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Fast time optical variability in Be/X-ray binaries

Cited by 6 publications

References 199 publications

Multiwavelength observations of KS 1947+300

Multiwavelength observations of KS 1947+300

Long-term optical variability of the Be/X-ray binary GRO J2058+42

Long-term optical variability of the Be/X-ray binary GRO J2058+42

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