Optical observations of the X-ray binary V1727 Cygni (=4U 2129+47) during a low state - Some unexpected results

Thorstensen, J. R.; Brownsberger, K. R.; Mook, D. E.; Berg, Chris; Bramson, Jim; Borden, Doug; Eisenthal, Josh; Fischer, Eric S.; Hamilton, Dave; Huettner, Steven; Kokko, Kenneth E.; Miele, Frank; Nichols, Steve; Scheible, Paul; Usadi, A.; Walsh, Rob; Wlodkowsi, Paul; Remillard, Ronald A.; McClintock, Jeffrey E.; Koo, David C.; Charles, P. A.

doi:10.1086/166847

Cited by 13 publications

(7 citation statements)

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“…At the 6.3 kpc distance of 4U 2129+47, and with A V = 1.5, this disk would have V ∼ 24.5. The quiescent counterpart has V = 17.9, so even if the disk were 100% modulated we would expect a fractional modulation of only ∼ 0.2%, which is well below the observed limit of 1.2% amplitude (99% confidence, Thorstensen et al 1988).…”

Section: Discussionmentioning

confidence: 61%

“…We note that this A V is measured to the F7IV counterpart of 4U2129+47, which is clearly not the secondary transferring mass to the neutron star. In using this A V and a spectroscopic distance of 6.3 kpc (Cowley & Schmidtke 1990) we are implicitly assuming that this star is in the physical proximity of the mass transferring binary (Thorstensen et al 1988, Garcia et al 1989, Cowley & Schmidtke 1990, van Paradijs & McClintock 1995 Once again, these results are fairly insensitive to the value of N H assumed, in that a 50% increase results in only a 10% drop in best fit temperature and a 40% increase in the emitted bolometric luminosity. The 0.5-10.0 keV band contains ∼ 80% of the bolometric luminosity at the best fit temperature, and ∼ 70% at the lowest allowed temperature.…”

Section: U 2129+47 Quiescent Spectrummentioning

confidence: 99%

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Two Neutron Star Soft X-Ray Transients in Quiescence: 4U 2129+47 and EXO 0748−676

Garcia

Callanan

1999

The Astronomical Journal

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We report on x-ray observations of two soft x-ray transients containing neutron stars, 4U 2129+47 and EXO 0748-676. Our emphasis is on the quiescent properties of these sources.The x-ray spectrum and lightcurve of the eclipsing Low-Mass X-ray Binary (LMXB) 4U 2129+47 was measured with the ROSAT PSPC during its current quiescent state. The quiescent x-ray luminosity of ∼ 10 32.7 erg s −1 and blackbody temperature of kT ∼ 0.21 keV are similar to other quiescent LMXB. The quiescent x-ray light curve appears to show orbital modulation, but the statistics are insufficient to distinguish between a v-shaped partial eclipse (as seen in the high state) or a total, square wave eclipse. The similarity in the luminosity and temperature to other (non-eclipsing) quiescent LMXB implies that the vertical structure in the disk which blocked our direct view of the neutron star in the high state has collapsed, and the neutron star is seen directly.EXO 0748-676 was serendipitously observed with the Einstein IPC in quiescence before it was discovered as a bright transient with EXOSAT. Our re-analysis of this quiescent observation finds L x ∼ 10 34.0 erg s −1 , and blackbody temperature of kT ∼ 0.22 keV, again similar to other LMXBs in quiescence.

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Section: Discussionmentioning

confidence: 61%

Section: U 2129+47 Quiescent Spectrummentioning

confidence: 99%

Two Neutron Star Soft X-Ray Transients in Quiescence: 4U 2129+47 and EXO 0748−676

Garcia

Callanan

1999

The Astronomical Journal

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“…The extended interval of X-ray quiescence prompted a flurry of observations to determine the ellipsoidal variations of the secondary without the disturbing effect of X-ray heating in order to verify the anomalous low neutron star mass. Surprisingly, neither photometric variations nor radial velocity variations could be detected (Thorstensen et al 1988;Kaluzny 1988;Chevalier et al 1989;Garcia et al 1989;). The star that is visible in the low state optical spectrum appears to be a normal F8 IV star ), although Kaluzny (1988) finds that the colors of the object in the low state are incompatible with colors of an ordinary star.…”

Section: V1727 Cygmentioning

confidence: 97%

Hubble Space TelescopeImaging of Bright Galactic X‐Ray Binaries in Crowded Fields

Deutsch

Margon

Wachter

et al. 1996

ApJ

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We report high spatial resolution HST imagery and photometry of three well-studied, intense Galactic X-ray binaries, X2129]470, CAL 87, and GX 17]2. All three sources exhibit important anomalies that are not readily interpreted by conventional models. Each source also lies in a severely crowded Ðeld, and in all cases the anomalies would be removed if much of the light observed from the ground in fact came from a nearby, thus far unresolved superposed companion. For V1727 Cyg (X2129]470), we Ðnd no such companion. We also present an HST FOS spectrum and broadband photometry which is consistent with a single, normal star. The supersoft LMC X-ray source CAL 87 was already known from ground-based work to have a companion separated by from the optical counterpart ; our HST 0A .9 images clearly resolve these objects and yield the discovery of an even closer, somewhat fainter additional companion. Our photometry indicates that contamination is not severe outside eclipse, where the companions only contribute 20% of the light in V , but during eclipse more than half of the V light comes from the companions. The previously determined spectral type of the CAL 87 secondary may need to be reevaluated due to this signiÐcant contamination, with consequences on inferences of the mass of the components. We Ðnd no companions to NP Ser (\X1813[14, \ GX 17]2). However, for this object we point out a small but possibly signiÐcant astrometric discrepancy between the position of the optical object and that of the radio source which is the basis for the identiÐcation. This discrepancy needs to be clariÐed.

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“…It was expected that optical observations of the 4U 2129+47 system in quiescence would reveal strong ellipsoidal variations. Instead, Thorstensen et al (1988) observed a system exhibiting an F star with no detectable orbital modulations. Comparison of the position of this quiescent optical source with the position of the optical counterpart of 4U 2129+47 in outburst revealed the two sources to be coincident within 0.3 ′′ ; therefore, Thorstensen et al (1988) considered the possibility that the 4U 2129+47 system might be a triple.…”

Section: Astrometrymentioning

confidence: 99%

“…After 4U 2129+47 entered quiescence, optical modulation was no longer observed over its 5.24 hr binary period. Instead of finding its expected M or K type companion, a nearby late F type star was found (Kaluzny 1988;Thorstensen et al 1988;Chevalier et al 1989;Garcia et al 1989;Cowley & Schmidtke 1990), which has led to the hypothesis that the 4U 2129+47 system is a hierarchical triple. The F star would be in a few month orbit about the inner binary, which in turn could lead to modulations of the binary eccentricity on 50 yr time scales (Garcia et al 1989).…”

Section: Introductionmentioning

confidence: 99%

Hiding in Plain Sight:ChandraObservations of the Quiescent Neutron Star 4U 2129+47 in Eclipse

Nowak

Heinz²,

Begelman

2002

ApJ

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During a previous outburst phase, the neutron star 4U 2129+47 exhibited evidence for a spatially extended Accretion Disk Corona (ADC) via broad, partial X-ray eclipses occurring periodically on the 5.24 hr orbit. Since 1983, however, 4U 2129+47 has entered a quiescent state several orders of magnitude fainter. We have performed a 37 ksec (≈2 binary orbits) Chandra observation of 4U 2129+47 to determine whether an extended coronal structure also exists in quiescence. Total eclipses are found, and the rapidity of the eclipse ingress and egress are used to place upper limits on the size of the X-ray source. The spectrum is found to be comprised of a soft component plus a fairly hard power law tail. The former is seen to be sinusoidally modulated over the orbital period in a manner consistent with neutral column variations, possibly due to the interaction of an accretion stream with a (small) disk about the neutron star. We fit realistic neutron star atmosphere models to the soft spectra, and comment on the consistency of the spectra with cooling neutron star models. It has been previously suggested that the 4U 2129+47 system is a hierarchical triple, with the outer body being an F star. We use differential astrometry to show that the X-ray point source and F star are spatially coincident to within 0.1 ′′ . We further compare newly determined upper limits for the extrinsic neutral column to the reddening of the F star. Finally, we discuss how future X-ray observations can further constrain models of quiescent neutron star emission, as well as directly verify the triple hypothesis.

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Optical observations of the X-ray binary V1727 Cygni (=4U 2129+47) during a low state - Some unexpected results

Cited by 13 publications

References 0 publications

Two Neutron Star Soft X-Ray Transients in Quiescence: 4U 2129+47 and EXO 0748−676

Two Neutron Star Soft X-Ray Transients in Quiescence: 4U 2129+47 and EXO 0748−676

Hubble Space TelescopeImaging of Bright Galactic X‐Ray Binaries in Crowded Fields

Hiding in Plain Sight:ChandraObservations of the Quiescent Neutron Star 4U 2129+47 in Eclipse

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