Observation of X-ray eclipses from LMC X-4

Li, F.; Rappaport, S.; Epstein, A.

doi:10.1038/271037a0

Cited by 39 publications

(32 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Optical photometric and spectroscopic studies of this star (Chevalier and Ilovaisky 1977;Hutchings et al 1978) conclusively proved that the system is a binary, and the orbital period P orb ≃ 1.408 days was determined from the modulation of its optical emission. This result was also confirmed in X-rays based on the observation of eclipses (Li et al 1978;White 1978), suggesting a high binary inclination. Observations show that many X-ray sources exhibit a long term-variability in their emission on time scales from several tens of days to several years.…”

Section: Introductionsupporting

confidence: 67%

Determination of parameters of Long-Term variability of the X-ray pulsar LMC X-4

2015

View full text Add to dashboard Cite

-We have investigated the temporal variability of the X-ray flux measured from the highmass Xray binary LMCX-4 on time scales from several tens of days to tens of years, i.e., exceeding considerably the orbital period (1.408 days). In particular, we have investigated the 30-day cycle of modulation of the X-ray emission from the source (superorbital or precessional variability) and refined the orbital period and its first derivative. We show that the precession period in the time interval 1991-2015 is near its equilibrium value P sup = 30.370 days, while the observed historical changes in the phase of this variability can be interpreted in terms of the "red noise" model. We have obtained an analytical law from which the precession phase can be determined to within 5% in the entire time interval under consideration. Using archival data from several astrophysical observatories, we have found 43 X-ray eclipses in LMC X-4 that, together with the nine eclipses mentioned previously in the literature, have allowed the parameters of the model describing the evolution of the orbital period to be determined. As a result, the rate of change in the orbital periodṖ orb /P orb = (1.21 ± 0.07) × 10 −6 yr −1 has been shown to be higher than has been expected previously.

show abstract

Section: Introductionsupporting

confidence: 67%

Determination of parameters of Long-Term variability of the X-ray pulsar LMC X-4

2015

View full text Add to dashboard Cite

show abstract

“…The X-ray pulsar LMC X-4 in the Large Magellanic Cloud (LMC) (the distance to the object is d = 50 kpc) is a high-mass binary with a pulsation period of ∼ 13.5 s (Kelley et al 1983), in which the compact object is eclipsed by its optical companion, an O8 star of the 14th magnitude with a mass of 20 M ⊙ (Chevalier and Ilovaisky 1977), every ∼1.408 days (Li et al 1978;Lang et al 1981; Levine et al 2000). Levine et al (2000) provided the following orbital parameters for the binary: a x sini = 26.333 ± 0.019 light seconds, the eccentricity e < 0.003(2σ), and the epoch of the zero orbital phase T 0 =MJD51110.86571.…”

Section: Introductionmentioning

confidence: 99%

“…We see a tendency for the radiation from the object under study to soften as it approaches an eclipse, but this dependence breaks down immediately after the eclipse. The hardness during the eclipses themselves is not shown in the figure, because no statistically significant flux can be recorded from the source.The dashed lines indicate the eclipse ephemerides taken from the papers by Li et al (1978), Lang et al (1981), and Levine et al (2000). Note that the orbital period in the binary is highly stable and has been almost constant over more than twenty years of the pulsar's studies.…”

mentioning

confidence: 99%

Long-term INTEGRAL and RXTE observations of the X-ray pulsar LMC X-4

Tsygankov

Lutovinov

2005

Astron. Lett.

View full text Add to dashboard Cite

We analyze the observations of the X-ray pulsar LMC X-4 performed by the INTEGRAL observatory and the All-Sky Monitor (ASM) of the RXTE observatory over a wide energy range. The observed hard X-ray flux from the source is shown to change by more than a factor of 50 (from ∼ 70 mCrab in the high state to ∼ 1.3 mCrab in the low state) on the time scale of the accretion-disk precession period, whose mean value for 1996-2004 was determined with a high accuracy, P prec = 30.275 ± 0.004 days. In the low state, a flare about 10 h in duration was detected from the source; the flux from the source increased by more than a factor of 4 during this flare. The shape of the pulsar's broadband spectrum is essentially invariable with its intensity; no statistically significant features associated with the possible resonance cyclotron absorption line were found in the spectrum of the source. c 2005 Pleiades Publishing Inc.Key words: pulsars, neutron stars, X-ray sources. * E-mail: st@hea.iki.rssi.ru INTRODUCTIONThe X-ray pulsar LMC X-4 in the Large Magellanic Cloud (LMC) (the distance to the object is d = 50 kpc) is a high-mass binary with a pulsation period of ∼ 13.5 s (Kelley et al. 1983), in which the compact object is eclipsed by its optical companion, an O8 star of the 14th magnitude with a mass of 20 M ⊙ (Chevalier and Ilovaisky 1977), every ∼1.408 days (Li et al. 1978;Lang et al. 1981;Levine et al. 2000). Levine et al. (2000) provided the following orbital parameters for the binary: a x sini = 26.333 ± 0.019 light seconds, the eccentricity e < 0.003(2σ), and the epoch of the zero orbital phase T 0 =MJD51110.86571. Lang et al. (1981) pointed to the existence of a superorbital period in the binary, ∼ 30.5 days, within which the intensity of the source changes by a factor of about 60. These authors also assumed that this effect is produced by the blockage of direct X-rays by a precessing accretion disk tilted with respect to the orbital plane, much as is the case in the binary Her X-1 (Tananbaum et al. 1972). Based on the measurements of almost the same Xray flux observed from the source during eclipses in its low and high states, Woo et al. (1995) concluded that the intrinsic luminosity of the pulsar is constant, which also confirms the assumption made by Lang et al. (1981). Having analyzed the RXTE and GINGA observations, Paul and Kitamoto (2002) estimated the rate of decrease in the precession period of the accretion disk to beṖ ∼ −2 × 10 −5 s s −1 .The flaring activity of LMC X-4 has been widely discussed in the literature (see, e.g., Epstein et al. 1977;Skinner et al. 1980;Kelley et al. 1983;Levine et al. 1991). A flare with a duration from dozens of seconds to dozens of minutes is detected from the source during its high state, on average, once a day. However, there is also evidence (Woo et al. 1995) for the presence of bursts in the low state.In different periods, the pulsar LMC X-4 demonstrates both a spin-down and a spin-up, suggesting that its period is close to its equilibrium value. In this case, according to the ...

show abstract

“…X-ray pulsations with a spin period of 13.5 s were discovered by Kelley et al (1983) which was later detected in the EXOSAT observations of the source even during the quiescent period and several 1 minute flares (Pietsch et al 1985). X-ray eclipses with a 1. d 4 recurring period were discovered by Li et al (1978) and White (1978). The X-ray intensity varies by a factor of ∼60 between high and low states with a periodic cycle time of 30.5 day (Lang et al 1981).…”

Section: Introductionmentioning

confidence: 99%

Spectral variations of the X-ray binary pulsar LMC X-4 during its long period intensity variation and a comparison with Her X-1

Naik

Paul

2003

A&A

View full text Add to dashboard Cite

Abstract. We present spectral variations of the binary X-ray pulsar LMC X-4 using the RXTE/PCA observations at different phases of its 30.5 day long super-orbital period. Only out of eclipse data were used for this study. During the high state of the super-orbital period of LMC X-4, the spectrum is well described by a high energy cut-off power-law with a photon index in the range of 0.7−1.0 and an iron emission line. In the low state, the spectrum is found to be flatter with power-law photon index in the range 0.5−0.7. A direct correlation is detected between the continuum flux in 7−25 keV energy band and the iron emission line flux. The equivalent width of the iron emission line is found to be highly variable during the low intensity state, whereas it remains almost constant during the high intensity state of the super-orbital period. It is observed that the spectral variations in LMC X-4 are similar to those of Her X-1 (using RXTE/PCA data). These results suggest that the geometry of the region where the iron line is produced and its visibility with respect to the phase of the super-orbital period is similar in LMC X-4 and Her X-1. A remarkable difference between these two systems is a highly variable absorption column density with phase of the super-orbital period that is observed in Her X-1 but not in LMC X-4.

show abstract

Observation of X-ray eclipses from LMC X-4

Cited by 39 publications

References 12 publications

Determination of parameters of Long-Term variability of the X-ray pulsar LMC X-4

Determination of parameters of Long-Term variability of the X-ray pulsar LMC X-4

Long-term INTEGRAL and RXTE observations of the X-ray pulsar LMC X-4

Spectral variations of the X-ray binary pulsar LMC X-4 during its long period intensity variation and a comparison with Her X-1

Contact Info

Product

Resources

About