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

Reig, P.; Tzouvanou, A.; Blinov, D.; V., Pantoulas,

doi:10.1051/0004-6361/202245598

Cited by 6 publications

(3 citation statements)

References 62 publications

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“…Optical observations of this companion star obtained in 2021 classified it as spectral type B1-3e III-V, indicating that MAXI J0655−013 is an example of a Be X-ray Binary (BeXRB; Zaznobin et al 2022). Further optical observations in September 2022 suggested that the companion has spectral type O9.5-B0V, confirming the classification of MAXI J0655−013 as a BeXRB (Reig et al 2022).…”

Section: Introductionsupporting

confidence: 63%

Accretion Spin-up and a Strong Magnetic Field in the Slow-spinning Be X-Ray Binary MAXI J0655-013

Pike,

Sugizaki,

Eijnden

et al. 2023

ApJ

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We present Monitor of All-sky X-ray Image (MAXI) and Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the Be X-ray binary, MAXI J0655−013, in outburst. NuSTAR observed the source once early in the outburst, when spectral analysis yields a bolometric (0.1–100 keV), unabsorbed source luminosity of L bol = 5.6 × 1036 erg s−1, and a second time 54 days later, by which time the luminosity had dropped to L bol = 4 × 1034 erg s−1 after first undergoing a dramatic increase. Timing analysis of the NuSTAR data reveals a neutron star spin period of 1129.09 ± 0.04 s during the first observation, which decreased to 1085 ± 1 s by the time of the second observation, indicating spin-up due to accretion throughout the outburst. Furthermore, during the first NuSTAR observation, we observed quasi-periodic oscillations (QPOs) with centroid frequency ν 0 = 89 ± 1 mHz, which exhibited a second harmonic feature. By combining the MAXI and NuSTAR data with pulse period measurements reported by Fermi/GBM, we are able to show that apparent flaring behavior in the MAXI light curve is an artifact introduced by uneven sampling of the pulse profile, which has a large pulsed fraction. Finally, we estimate the magnetic field strength at the neutron star surface via three independent methods, invoking a tentative cyclotron resonance scattering feature at 44 keV, QPO production at the inner edge of the accretion disk, and spin-up via interaction of the neutron star magnetic field with accreting material. Each of these result in a significantly different value. We discuss the strengths and weaknesses of each method and infer that MAXI J0655−013 is likely to have a high surface magnetic field strength, B s > 1013 G.

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Section: Introductionsupporting

confidence: 63%

Accretion Spin-up and a Strong Magnetic Field in the Slow-spinning Be X-Ray Binary MAXI J0655-013

Pike,

Sugizaki,

Eijnden

et al. 2023

ApJ

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“…The long-term variability of CPD −29 2176 is best explored with the time series from ground-based surveys such as ASAS, shown in Figure 4. The photometric data do not show evidence of eclipses but do show long-term variations similar to other Be stars (Labadie- Bartz et al 2017;Bernhard et al 2018), including Be XRBs (Reig & Fabregat 2015;Reig et al 2023). In the ASAS data, we see multiple peaks in the light curve with a timescale of ∼600 days.…”

Section: Photometric Variabilitymentioning

confidence: 57%

Optical Properties and Variability of the Be X-Ray Binary CPD-29 2176

Pavao,

Richardson,

Labadie-Bartz

et al. 2023

ApJ

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Be X-ray binaries (Be XRBs) are high-mass X-ray binaries, with a neutron star or black hole orbiting and accreting material from a nonsupergiant B-star that is rotating at a near critical rate. These objects are prime targets to understand past binary interactions as the neutron star or black hole progenitor likely experienced Roche lobe overflow to spin up the Be star we observe now. The stellar variability can then allow us to explore the stellar structure of these objects. It was recently demonstrated that the high-mass X-ray binary CPD −29 2176 descended from an ultrastripped supernova and is a prime target to evolve into an eventual binary neutron star and kilonova. We present the photometric variability from both TESS and ASAS along with the spectral properties and disk variability of the system in this paper. All of the optical lines are contaminated with disk emission except for the He ii λ4686 absorption line. The disk variability timescales are not the same as the orbital timescale, but could be related to the X-ray outbursts that have been recorded by Swift. We end our study with a discussion comparing CPD −29 2176 to classical Be stars and other Be X-ray binaries, finding the stellar rotation to be near a frequency of 1.5 cycles day−1, and exhibiting incoherent variability in three frequency groups.

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“…Some of these mechanisms involve variations in the companion star and/or the circumstellar disk of the Be star and can produce optical variability of tenths of magnitudes. They comprise different scenarios such as ejections of matter from the Be star (Hubert & Floquet 1998;Mennickent et al 2002), precession, and/or warping or changes in the inclination of the circumstellar disk (Okazaki et al 2013;Martin et al 2014;Martin & Franchini 2019), as well as the formation and dissipation of the circumstellar disk (see for example Reig et al 2023).…”

Section: Introductionmentioning

confidence: 99%

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

Cited by 6 publications

References 62 publications

Accretion Spin-up and a Strong Magnetic Field in the Slow-spinning Be X-Ray Binary MAXI J0655-013

Accretion Spin-up and a Strong Magnetic Field in the Slow-spinning Be X-Ray Binary MAXI J0655-013

Optical Properties and Variability of the Be X-Ray Binary CPD-29 2176

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

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