Multiwavelength observations of <i>Swift</i> J0243.6+6124 from 2017 to 2022

Liu, Wei; Yan, Jing-Zhi; Reig, P.; Wang, Xiaofeng; Xiao, G. C.; Lin, Han; Zhang, Xinhan; Sai, Hanna; Chen, Zhihao; Yan, Shengyu

doi:10.1051/0004-6361/202243878

Cited by 9 publications

(8 citation statements)

References 25 publications

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“…These delays imply that the continuum and line emission are anticorrelated for a certain period of time (i.e., the time elapsed between the two peaks). This result has been reported in many other BeXBs: Swift J0243.6+6124 (Liu et al 2022), RX J0440.9+4431 (Yan et al 2016), 1A 0535+26 (Clark et al 1999;Yan et al 2012), 4U 0115+63 (Reig et al 2007), and SAX J2103.5+4545 (Camero et al 2014). Interestingly, the X-ray outbursts occur close to the EW(Hα) maxima.…”

Section: Line and Continuum Emissionsupporting

confidence: 84%

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: Line and Continuum Emissionsupporting

confidence: 84%

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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“…1. This oscillation has a quasi-period of ∼1200 d. Similar variability over a period of ∼1000 d was reported in the past by Nesci (2017) A45, page 4 of 16 These modulations can be explained by the replenishment and dissipation of the circumstellar disk, and this explanation is in agreement with the evolution of the EW(Hα) line (Reig et al 2020;Liu et al 2022b). In order to obtain an estimation of the emission from the Be star and the circumstellar disk in the V-Johnson band, we performed a cubic spline fit to the points outside the outburst (we did not consider the points between MJD 57850 and 58300 MJD) on the long-term V-Johnson light curve (see Fig.…”

Section: Isolation Of the Extra Optical/uv Emission Due To The Outburstsupporting

confidence: 85%

“…In this case, we would only expect to observe the contribution of the Be star and the circumstellar disk. From the long-term variability of the optical light curves, and from the values of the equivalent width (EW) of the Hα line, we expect that the contribution from the Be circumstellar disk is minimum at that epoch (Reig et al 2020;Liu et al 2022b). For the SED fit, we built a grid of values of E(B − V) from 0.9 to 1.4 with step 0.01, and used the theoretical spectra of a O9.5V star of T eff = 32 000 K, log g = 4.0, and Z = Z from the stellar atmosphere models by Castelli & Kurucz (2003), assuming the extinction law from Fitzpatrick (1999).…”

Section: Estimation Of the Interstellar Reddeningmentioning

confidence: 99%

“…Indeed, for some BeXBs, signatures of tidal warped circumstellar disks have been observed during giant X-ray outbursts (Moritani et al 2013;Reig & Blinov 2018). However, no signs of warping and/or eccentricity have been found in the profiles of the optical emission lines during the giant outburst of Swift J0243.6+6124 (Reig et al 2020;Liu et al 2022b), although we cannot rule out the presence of a tilted disk with the tilting axis almost perpendicular to the line of sight (in this case the emission lines would also be singlepeaked).…”

Section: Description Of the Modelmentioning

confidence: 99%

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Unveiling the origin of the optical and UV emission during the 2017 giant outburst of the Galactic ULX pulsar Swift J0243.6+6124

Alfonso-Garzón,

van den Eijnden,

Kuin

et al. 2024

A&A

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From late September 2017 to January 2018, the Be X-ray binary (BeXB) Swift J0243.6+6124 underwent a giant outburst that was unprecedently bright. The reported X-ray luminosities were so high that the system was classified as an ultraluminous X-ray source (ULX). It was also the first BeXB pulsar to show radio jet emission. The source was not only bright in X-rays and radio, but also in the optical and ultraviolet (UV) wavelenghts as well. In this work, we aim to understand the origin of the observed optical/UV fluxes simultaneous to the X-ray emission. We studied the optical/UV light curves in comparison with the X-ray fluxes along the outburst. We considered the main mechanisms that can explain the optical/UV emission in X-ray binaries. Due to the tight correlation observed between the optical/UV and X-ray light curves, reprocessing of X-rays seems to be the most plausible explanation. We calculated the timescales of the light curve decays and studied the correlation indexes between the optical and X-ray emission. Finally, we built a physical model that considers the X-ray heating of the surface of the donor star, irradiation of the accretion disk, and emission from a viscously heated accretion disk, so that we could reproduce the observed optical/UV spectral energy distributions (SEDs) along the outburst. In our model, we considered the Be circumstellar disk to be co-planar to the orbit and then we neglected its irradiation in the current model. As an input for the model, we used as incident X-ray luminosities those calculated from the bolometric X-ray fluxes obtained from the spectral fit of the Swift /XRT and BAT observations. The timescales of the exponential decay of the outburst are between two and four times longer for the UV and optical light curves than for the X-ray light curve. The correlation index between the optical/UV and X-ray fluxes varies between optical/UV filters and when different X-ray bands are considered and is larger for the rise than for the decay phase of the outburst for the fluxes at redder wavelengths. The modelling of the SED shows that X-ray heating of the companion star surface is the main mechanism contributing to the UV emission and contributes significantly to the optical emission during the whole outburst. The X-ray irradiation of the accretion disk is necessary to reproduce the optical observed fluxes from MJD 58047 to 58120 and contributes significantly to the UV fluxes close to the peak of the outburst. As a first attempt, the fits yield an increasing value of the outer radius of the accretion disk along the outburst. An alternative interpretation points to variations in the geometry of the inner flow and the fraction of reprocessed X-ray emission during the outburst. On the other hand, variations in the geometry of the Be circumstellar disk could also play a role, but they have not been considered in the current model. Reprocessing of X-rays via the X-ray heating of the Be star surface and as irradiation of the accretion disk is the main mechanism that can reproduce the observed optical/UV emission during the 2017-2018 giant outburst of

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“…These delays imply that the continuum and line emission are anticorrelated for a certain period of time (i.e., the time elapsed between the two peaks). This result has been reported in many other BeXBs: Swift J0243.6+6124 (Liu et al 2022), RX J0440.9+4431 (Yan et al 2016), 1A 0535+26 (Clark et al 1999;Yan et al 2012), 4U 0115+63 (Reig et al 2007), and SAX J2103.5+4545 (Camero et al 2014). Interestingly, the Xray outbursts occur close to the EW(Hα) maxima.…”

Section: Line and Continuum Emissionsupporting

confidence: 84%

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.

show abstract

Multiwavelength observations of Swift J0243.6+6124 from 2017 to 2022

Cited by 9 publications

References 25 publications

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

Unveiling the origin of the optical and UV emission during the 2017 giant outburst of the Galactic ULX pulsar Swift J0243.6+6124

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

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