Very long-term X-ray variations in LMXBs: solar cycle-like variations in the donor?

Kotze, M.; Charles, P. A.

doi:10.1111/j.1745-3933.2009.00790.x

Cited by 21 publications

(17 citation statements)

References 24 publications

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“…Since there is no significant mass transfer taking place in the system at the current time, this cannot be the cause of the apparent orbital period changes. One would have to invoke another mechanism, such as the Applegate effect (Applegate & Patterson 1987;Applegate 1992;Kotze & Charles 2010), to explain the short-timescale changes in the orbit. We focus here on a more interesting and, in our view, more likely scenario, i.e., that there is a third body in the system.…”

Section: Evidence For a Third Star In Kic 9164561mentioning

confidence: 99%

DISCOVERY OF TWO NEW THERMALLY BLOATED LOW-MASS WHITE DWARFS AMONG THEKEPLERBINARIES

Rappaport

Nelson

Levine

et al. 2015

ApJ

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We report the discovery of two new low-mass, thermally bloated, hot white dwarfs among the Kepler sample of eclipsing binaries. These are KIC 9164561 and KIC 10727668 with orbital periods of 1.2670 and 2.3058 days, respectively. The current primary in both systems is an A star of about 2  M . This brings the number of similar binaries among the Kepler sample to six, and the two new systems have the shortest orbital periods among them. The white dwarf (WD) in KIC 9164561 has the largest thermal bloating, compared to its cold degenerate radius, of about a factor of 14. We utilize radial velocity measurements of the A star in KIC 9164561 to determine the WD mass rather accurately:. The mass of the WD in KIC 10727668 is based on the Doppler boosting signal in the Kepler photometry and is less accurately determined to be . Based on the inferred radii and effective temperatures of these two white dwarfs, we are able to make an independent theoretical estimate of their masses to within ∼0.01  M based on evolutionary models of their cooling history after they lose their hydrogen-rich envelopes. We also present evidence that there is a third body in the KIC 9164561 system with an orbital period of 8-14 yr.

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Section: Evidence For a Third Star In Kic 9164561mentioning

confidence: 99%

DISCOVERY OF TWO NEW THERMALLY BLOATED LOW-MASS WHITE DWARFS AMONG THEKEPLERBINARIES

Rappaport

Nelson

Levine

et al. 2015

ApJ

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“…Changes in the matter transfer rate from the companion due to a Solar-like magnetic cycle have been suggested as the origin of the long-term modulation in GX 3+1 and other persistent Atoll sources (Kotze & Charles, 2010). Z sources could be less affected due to the output from the donor exceeding the Eddington limit for accretion onto the NS; the local accretion/emission rate remains near the Eddington limit and the surplus matter gets ejected.…”

Section: Resultsmentioning

confidence: 99%

“…GX 3+1 is a persistently bright Atoll-type neutron star Low-Mass X-ray Binary (NS LMXB) that has long been known to show flux variations of a factor of ∼2-3 on time scales of several years (Makishima et al, 1983;Asai et al, 1993;Kotze & Charles, 2010). Kuulkers & van der Klis (2000) found one X-ray burst that shows evidence for radius expansion of the neutron star photosphere during a thermonuclear runaway, suggesting temporary super-Eddington emission.…”

Section: Introductionmentioning

confidence: 99%

A comparison between the spectral and long term timing properties of GX 3+1, GX 5-1 and GX 13+1

Savolainen¹,

Hannikainen²,

Paizis³

et al. 2011

Proceedings of 8th INTEGRAL Workshop “The Restless Gamma-Ray Universe” — PoS(INTEGRAL 2010)

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Using GX 3+1 as an example of a bright Atoll, GX 5-1 as an example of a Z source, and GX 13+1 as a peculiar hybrid, we take a look at the spectral and long-term time evolution differences in these three neutron star Low-Mass X-ray Binaries representing different subtypes. We utilize a recently developed spectral model based on mixed thermal and bulk motion Comptonization of soft seed photons from the accretion disc and the neutron star surface. The hard X-ray tails exhibited by GX 5-1 and GX 13+1 are attributed to efficient bulk motion Comptonization, which is not present in GX 3+1 due to too low or too high a local accretion rate. Accreting well below the Eddington limit also enables GX 3+1 to exhibit amplitude modulation presumably due to changes in the accretion output from the companion star, visible in the RXTE/ASM light curve on a time scale of ∼6 years.8th INTEGRAL Workshop‚ "The Restless Gamma-ray Universe",

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“…But these cycles did not show any strict periodicity and are decades long. A similar possibility was explored for low mass X-ray binaries (Kotze & Charles 2010). The spectral class of the secondary star in FS Aur is not known, but is expected to be a very late M-dwarf, or even brown dwarf.…”

Section: Discussionmentioning

confidence: 99%

A dynamical explanation for a long-term modulation in the light curve of FS Aurigae

Chavez

Tovmassian

Aguilar

et al. 2012

A&A

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Aims. FS Aur is an unusual cataclysmic variable, which in addition to its spectroscopically determined orbital period of 85.7 min exhibits spectroscopic and photometric periods of 147 and 205 min, correspondingly, which are attributed to the period of the fast rotating and freely precessing magnetic white dwarf. We aim to study the origin of a very long term variability observed in the light curve of FS Aur accumulated by us and in the AAVSO International Database over the past thirteen years. Methods. Discrete Fourier transform algorithm and Scargle-Lomb least-squares spectral analysis were used for the period analysis of the observational data. A 12th-order Runge-Kutta-Nyström integrator was used to conduct numerical simulations of a three-body system that is invoked to explain the observed long-term variability in the FS Aur light curve, which is probably periodic. Results. We report here a newly discovered ∼2-mag modulation of the light curve of FS Aur with a ∼900-day period. The huge disparity with the previous periods makes this difficult to explain within the confines of the binary system. We propose a mechanism for this longer period: a modulation in the binary eccentricity, produced by the gravitational perturbation of a third object on a larger orbit. We first explore orbits with a period equal to the ∼900-day modulation and a high eccentricity that can produce a direct perturbation in the close binary system, and conclude that the shape of the time response does not match the observed light curve. However, putting the perturber on a circular, shorter period orbit at the proper location can induce a long-term secular modulation.Conclusions. There is a tight correlation between the perturber mass and orbital radius with the induced long-term modulation in the central binary. To explain the observed ∼900-day period, the perturber must be a substellar mass object with a probable mass between 25 to 64 times that of Jupiter. The presence of the third body in this system may be a clue for understanding other observational peculiarities.

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Very long-term X-ray variations in LMXBs: solar cycle-like variations in the donor?

Cited by 21 publications

References 24 publications

DISCOVERY OF TWO NEW THERMALLY BLOATED LOW-MASS WHITE DWARFS AMONG THEKEPLERBINARIES

DISCOVERY OF TWO NEW THERMALLY BLOATED LOW-MASS WHITE DWARFS AMONG THEKEPLERBINARIES

A comparison between the spectral and long term timing properties of GX 3+1, GX 5-1 and GX 13+1

A dynamical explanation for a long-term modulation in the light curve of FS Aurigae

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