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

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.

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

2019 ◽  
Vol 489 (2) ◽  
pp. 1797-1804 ◽  
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.

scholarly journals Disk Structure and Evolution Around the Neutron Star in Be/X-Ray Binaries

2004 ◽  
Vol 194 ◽  
pp. 230-230
Author(s):  
Kimitake Hayasaki ◽  
Atsuo T. Okazaki
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Orbital Plane ◽  
X Ray ◽  
Accretion Flow ◽  
Disk Structure ◽  
Disk Size ◽  
Short Period ◽  
Stage Process ◽  
X Ray Binaries

We investigate the accretion flow around the neutron star in Be/X-ray binaries, using a 3D SPH code and the data imported from simulations by Okazaki et al. (2002) and Okazaki & Hayasaki (2004) for both a coplanar system and a misaligned system in which the Bo-star disk is inclined from the binary orbital plane by 30 degrees, with a short period (Porb = 24.3 days) and moderate eccentricity (e = 0.34). We find that a non-steady accretion disk is formed around the neutron star in the misaligned case as well as in the coplanar case. The disk size in the misaligned system is significantly larger because of its higher angular momentum than that in the coplanar system. We also find that the disk also evolves via a two-stage process, which consists of the initial developing stage and the latar developed stage.

scholarly journals Proposed wavelength measurements of silicon X-ray spectra: Application to Vela X-1

2008 ◽  
Vol 86 (1) ◽  
pp. 183-189 ◽  
Author(s):  
D A Liedahl ◽  
G V Brown
Keyword(s):  
Neutron Star ◽  
Stellar Wind ◽  
Large Scale ◽  
Radiation Transport ◽  
Three Dimensional ◽  
Mass Transfer Process ◽  
Gravitational Potential Energy ◽  
X Ray ◽  
Close Orbit ◽  
Mass Capture

When a stellar wind from a massive star is captured by a neutron star in close orbit, gravitational potential energy is converted into hard X-radiation near the surface of the neutron star. The X-radiation, in turn, modifies the wind through heating and photoionization, which affects the dynamics of mass capture. We have begun a project to further elucidate this process, which involves time-dependent three-dimensional hydrodynamics, large-scale atomic physics calculations, and radiation transport, integrated in an attempt to derive a self-consistent “first principles” description of the mass transfer process. We anticipate that the high-resolution silicon X-ray spectrum, produced by innershell photoionization and photoexcitation, as measured by the Chandra observatory, will provide benchmarks for these calculations. However, theoretical wavelengths, which are required in order to draw inferences concerning the velocity field of the wind, are uncertain at the level of the likely Doppler shifts in the stellar wind. EBIT measurements could lead to a reliable set of wavelengths, thereby providing observational constraints on the physics that powers some of the brightest X-ray sources in the Galaxy. PACS Nos.: 32.30.Rj, 32.80.Fb, 32.80.Hd, 52.25.Os, 52.72.+v, 97.10.Me, 97.80.Jp

scholarly journals Multiwavelength observations of the Be-star/X-ray binary EXO2030+375 during outburst

1994 ◽  
Vol 162 ◽  
pp. 206-207
Author(s):  
A.J. Norton ◽  
M.J. Coe ◽  
C. Everall ◽  
P. Roche ◽  
L. Bildsten ◽  
...  
Keyword(s):  
Neutron Star ◽  
Emission Lines ◽  
Be Stars ◽  
Infrared Excess ◽  
X Ray ◽  
Circumstellar Material ◽  
Spin Period ◽  
Be Star ◽  
Star Surface ◽  
X Ray Binaries

EXO2030+375 consists of a neutron star in an eccentric 46 day orbit around a 20th magnitude Be-star companion (Coe et al., 1988; Parmar et al., 1989; Stollberg et al., 1993). The Be-star is thought to be surrounded by a shell/disc of material which is responsible for the infrared excess and Balmer emission lines which are characteristic of Be-stars in general. At periastron, the neutron star passes through this circumstellar material, giving rise to enhanced accretion onto the neutron star surface. As a result of this, the X-ray emission (pulsed at the neutron star spin period of 41.8s) increases dramatically, so producing the transient, outburst behaviour which is commonly seen in Be-star / X-ray binaries.

scholarly journals Eccentric Neutron Star Disk Driven Type II Outburst Pairs in Be/X-ray Binaries

2021 ◽  
Vol 923 (1) ◽  
pp. L18
Author(s):  
Alessia Franchini ◽  
Rebecca G. Martin
Keyword(s):  
Mass Transfer ◽  
Neutron Star ◽  
Type I ◽  
Type Ii ◽  
X Ray ◽  
Be Star ◽  
Orbital Periods ◽  
Hydrodynamical Simulations ◽  
X Ray Binaries ◽  
Lower Luminosity

Abstract Be star X-ray binaries are transient systems that show two different types of outbursts. Type I outbursts occur each orbital period while type II outbursts have a period and duration that are not related to any periodicity of the binary system. Type II outbursts may be caused by mass transfer to the neutron star from a highly eccentric Be star disk. A sufficiently misaligned Be star decretion disk undergoes secular Von Zeipel–Lidov–Kozai (ZLK) oscillations of eccentricity and inclination. Observations show that in some systems the type II outbursts come in pairs with the second being of lower luminosity. We use numerical hydrodynamical simulations to explore the dynamics of the highly misaligned disk that forms around the neutron star as a consequence of mass transfer from the Be star disk. We show that the neutron star disk may also be ZLK unstable and that the eccentricity growth leads to an enhancement in the accretion rate onto the neutron star that lasts for several orbital periods, resembling a type II outburst. We suggest that in a type II outburst pair, the first outburst is caused by mass transfer from the eccentric Be star disk while the second and smaller outburst is caused by the eccentric neutron star disk. We find that the timescale between outbursts in a pair may be compatible with the observed estimates.

scholarly journals Optical Counterparts to Be/X-ray Binaries in the Magellanic Clouds

1999 ◽  
Vol 192 ◽  
pp. 112-115
Author(s):  
David A. H. Buckley ◽  
James B. Stevens ◽  
Malcolm J. Coe
Keyword(s):  
Neutron Star ◽  
Magellanic Clouds ◽  
Optical Identification ◽  
Ccd Photometry ◽  
X Ray ◽  
Transient Nature ◽  
Be Star ◽  
Hα Emission ◽  
Early Type Stars ◽  
X Ray Binaries

We discuss the optical identification of 9 Be/X-ray binary optical counterparts of X-ray sources in the Magellanic clouds, most of them discovered in ROSAT observations. Imaging CCD photometry (using BV RC and Hα filters) was employed to search the typically 20 arcsec radius error circles for early-type stars exhibiting Hα emission. Spectroscopy of 5 candidates confirmed the presence of Hα emission. Based on the positional coincidences, we propose Be star optical counterparts to all of 9 X-ray sources: 6 from ROSAT and one each from ASCA, EXOSAT and HEAO-1. All of the sources exhibit the typical X-ray characteristics of Be/neutron star X-ray binaries: transient nature or strong variability, relatively hard X-ray spectra and, in 5 cases, detections of probable neutron star spin periods in the range 8.9 to 91.1 seconds.

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

2021 ◽  
Vol 503 (4) ◽  
pp. 6187-6201
Author(s):  
H Treiber ◽  
G Vasilopoulos ◽  
C D Bailyn ◽  
F Haberl ◽  
K C Gendreau ◽  
...  
Keyword(s):  
Neutron Star ◽  
Orbital Period ◽  
Orbital Plane ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Optical Data ◽  
Pulse Profile ◽  
X Ray ◽  
Binary Pulsar ◽  
Be Star

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.

scholarly journals Accretion Onto the Neutron Star in Be/X-ray Binaries

2004 ◽  
Vol 218 ◽  
pp. 449-450
Author(s):  
Kimitake Hayasaki ◽  
Atsuo T. Okazaki
Keyword(s):  
Neutron Star ◽  
High Resolution ◽  
Accretion Disk ◽  
Time Dependent ◽  
Disk Model ◽  
X Ray ◽  
Short Period ◽  
Be Star ◽  
X Ray Binaries ◽  
Resolution Simulation

We study accretion onto the neutron star in Be/X-ray binaries, using a 3D SPH code and the data imported from a high resolution simulation by Okazaki et al. (2002) for a coplanar system with a short period (Porb = 24.3 d) and moderate eccentricity (e = 0.34). We find that a time-dependent accretion disk is formed around the neutron star in Be/X-ray binaries. The disk shrinks after the periastron passage of the Be star and restores its radius afterwards. Our simulations show that the truncated Be disk model for Be/X-ray binaries is consistent with the observed X-ray behavior.

On the nature of the X-ray outbursts in Be/X-ray binaries

2018 ◽  
Vol 14 (S346) ◽  
pp. 146-148
Author(s):  
Jingzhi Yan ◽  
Wei Liu ◽  
Peng Zhang ◽  
Qingzhong Liu
Keyword(s):  
Neutron Star ◽  
Compact Object ◽  
Optical Emission ◽  
Light Curves ◽  
High Mass ◽  
Circumstellar Disk ◽  
X Ray ◽  
Be Star ◽  
The Relationship ◽  
X Ray Binaries

AbstractBe/X-ray binaries are a major subclass of high mass X-ray binaries. Two different X-ray outbursts are displayed in the X-ray light curves of such systems. It is generally believed that the X-ray outbursts are connected with the neutron star periastron passage of the circumstellar disk around the Be star. The optical emission of the Be star should be very important to understand the X-ray emission of the compact object. We have monitored several Be/X-ray binaries photometrically and spectroscopically in the optical band. The relationship between the optical emission and X-ray activity is described, which is very useful to explain the X-ray outbursts in Be/X-ray binaries.

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