RX J0529.8−6556: a BeXRB pulsar with an evolving optical period and out of phase X-ray outbursts

ABSTRACT We report the results of eROSITA and NICER observations of the 2020 June outburst of the Be/X-ray binary pulsar RX J0529.8−6556 in the Large Magellanic Cloud, along with the analysis of archival X-ray and optical data from this source. We find two anomalous features in the system’s behaviour. First, the pulse profile observed by NICER during maximum luminosity is similar to that observed by XMM–Newton in 2000, despite the fact that the X-ray luminosity was different by two orders of magnitude. In contrast, a modest decrease in luminosity in the 2020 observations generated a significant change in pulse profile. Secondly, we find that the historical optical outbursts are not strictly periodic, as would be expected if the outbursts were triggered by periastron passage, as is generally assumed. The optical peaks are also not coincident with the X-ray outbursts. We suggest that this behaviour may result from a misalignment of the Be star disc and the orbital plane, which might cause changes in the timing of the passage of the neutron star through the disc as it precesses. We conclude that the orbital period of the source remains unclear.

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The frequency of Kozai–Lidov disc oscillation driven giant outbursts in Be/X-ray binaries

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2250 ◽

2019 ◽

Vol 489 (2) ◽

pp. 1797-1804 ◽

Cited By ~ 2

Author(s):

Rebecca G Martin ◽

Alessia Franchini

Keyword(s):

Orbital Period ◽

Time Scale ◽

Orbital Plane ◽

Material Flows ◽

X Ray ◽

System Parameters ◽

Be Star ◽

Chaotic Nature ◽

X Ray Binaries ◽

Good Agreement

ABSTRACT Giant outbursts of Be/X-ray binaries may occur when a Be-star disc undergoes strong eccentricity growth due to the Kozai–Lidov (KL) mechanism. The KL effect acts on a disc that is highly inclined to the binary orbital plane provided that the disc aspect ratio is sufficiently small. The eccentric disc overflows its Roche lobe and material flows from the Be star disc over to the companion neutron star causing X-ray activity. With N-body simulations and steady state decretion disc models we explore system parameters for which a disc in the Be/X-ray binary 4U 0115+634 is KL unstable and the resulting time-scale for the oscillations. We find good agreement between predictions of the model and the observed giant outburst time-scale provided that the disc is not completely destroyed by the outburst. This allows the outer disc to be replenished between outbursts and a sufficiently short KL oscillation time-scale. An initially eccentric disc has a shorter KL oscillation time-scale compared to an initially circular orbit disc. We suggest that the chaotic nature of the outbursts is caused by the sensitivity of the mechanism to the distribution of material within the disc. The outbursts continue provided that the Be star supplies material that is sufficiently misaligned to the binary orbital plane. We generalize our results to Be/X-ray binaries with varying orbital period and find that if the Be star disc is flared, it is more likely to be unstable to KL oscillations in a smaller orbital period binary, in agreement with observations.

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Swift J053041.9-665426, a new Be/X-ray binary pulsar in the Large Magellanic Cloud

Astronomy and Astrophysics ◽

10.1051/0004-6361/201322335 ◽

2013 ◽

Vol 558 ◽

pp. A74 ◽

Cited By ~ 14

Author(s):

G. Vasilopoulos ◽

P. Maggi ◽

F. Haberl ◽

R. Sturm ◽

W. Pietsch ◽

...

Keyword(s):

Large Magellanic Cloud ◽

Magellanic Cloud ◽

X Ray ◽

Binary Pulsar

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Optical and ultraviolet line and continuum emission from the Large Magellanic Cloud X-ray Be star A0538-66

The Astrophysical Journal ◽

10.1086/166914 ◽

1988 ◽

Vol 335 ◽

pp. 147 ◽

Cited By ~ 4

Author(s):

K. M. V. Apparao ◽

S. P. Tarafdar

Keyword(s):

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Continuum Emission ◽

X Ray ◽

Be Star

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Mass-Capture Rate by the Neutron Star in Be/X-Ray Binaries

International Astronomical Union Colloquium ◽

10.1017/s0252921100152248 ◽

2004 ◽

Vol 194 ◽

pp. 144-145

Author(s):

A. T. Okazaki ◽

K. Hayasaki

Keyword(s):

Neutron Star ◽

Capture Rate ◽

Three Dimensional ◽

Orbital Plane ◽

Orbital Eccentricity ◽

X Ray ◽

Mass Capture ◽

Be Star ◽

X Ray Binaries

AbstractWe study the interaction between the Be-star disk and the neutron star in Be/X-ray binaries by three dimensional SPH simulations. We find that, the resonant, truncation of the Be disk works except for systems with extremely high orbital eccentricity or large misalignment angles between the Be disk and the orbital plane. Owing to the truncation, the mass-capture rate by the neutron star is sensitive both to the orbital eccentricity and to the angle of misalignment. It is single-peaked in coplanar systems and in systems with small misalignment angles, whereas it, becomes double-peaked in systems with large misalignment angles.

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Discovery of the 10.6 hr orbital period of CAL87: an eclipsing low-mass X-ray binary in the Large Magellanic Cloud

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/241.1.37p ◽

1989 ◽

Vol 241 (1) ◽

pp. 37P-41P ◽

Cited By ~ 19

Author(s):

P. J. Callanan ◽

G. Machin ◽

T. Naylor ◽

P. A. Charles

Keyword(s):

Orbital Period ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

X Ray ◽

Low Mass

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Nonperiodic Type I Be/X-Ray Binary Outbursts

The Astrophysical Journal ◽

10.3847/2041-8213/ac3a05 ◽

2021 ◽

Vol 922 (2) ◽

pp. L37

Author(s):

Rebecca G. Martin ◽

Alessia Franchini

Keyword(s):

Mass Transfer ◽

Neutron Star ◽

Orbital Period ◽

Type I ◽

X Ray ◽

Be Star

Abstract Type I Be/X-ray binary outbursts are driven by mass transfer from a Be star decretion disk to a neutron star companion during each orbital period. Treiber et al. recently observed nonperiodic type I outbursts in RX J0529.8–6556 that has unknown binary orbital properties. We show that nonperiodic type I outbursts may be temporarily driven in a low eccentricity binary with a disk that is inclined sufficiently to be mildly unstable to Kozai–Lidov oscillations. The inclined disk becomes eccentric and material is transferred to the neutron star at up to three locations in each orbit: when the neutron star passes the disk apastron or one of the two nodes of the disk. The timing and magnitude of each vary with the disk argument of periapsis and longitude of the ascending node that precess in opposite directions. Calculating the orbital period of the RX J0529.8–6556 system is nontrivial but we suggest it may be >300 days, longer than previous estimates.

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Aperiodic Flux Variability in A 0535+262

Symposium - International Astronomical Union ◽

10.1017/s0074180900055777 ◽

1996 ◽

Vol 165 ◽

pp. 313-319

Author(s):

Mark H. Finger ◽

Robert B. Wilson ◽

B. Alan Harmon ◽

William S. Paciesas

Keyword(s):

Neutron Star ◽

Gamma Ray ◽

Beat Frequency ◽

Power Spectra ◽

Center Frequency ◽

X Ray ◽

Binary Pulsar ◽

Transient Source ◽

Flux Variability ◽

Burst And Transient Source

A “giant” outburst of A 0535+262, a transient X-ray binary pulsar, was observed in 1994 February and March with the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory. During the outburst power spectra of the hard X-ray flux contained a QPO-like component with a FWHM of approximately 50% of its center frequency. Over the course of the outburst the center frequency rose smoothly from 35 mHz to 70 mHz and then fell to below 40 mHz. We compare this QPO frequency with the neutron star spin-up rate, and discuss the observed correlation in terms of the beat frequency and Keplerian frequency QPO models in conjunction with the Ghosh-Lamb accretion torque model.

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