Discovery of a 30.5 day periodicity in LMC X-4

Lang, F. L.; Levine, A.; Bautz, M. W.; Hauskins, S.; Howe, S. K.; Primini, F. A.; Lewin, W. H. G.; Baity, W. A.; Knight, F. K.; Rotschild, Robert; Petterson, J. A.

doi:10.1086/183545

Cited by 94 publications

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“…It has an intense magnetic field (La Barbera et al 2001), and it accretes material from the companion by stellar wind. As for Her X-1, an accretion disk that is thicker in the outer regions and truncated at the Alfén radius by the magnetic pressure, is also present (Lang et al 1981).…”

Section: Lmc X-4mentioning

confidence: 97%

An INTEGRAL hard X-ray survey of the Large Magellanic Cloud

Götz¹,

Mereghetti²,

Merlini

et al. 2006

A&A

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Two observation campaigns in 2003 and 2004 with the INTEGRAL satellite have provided the first sensitive survey of the Large Magellanic Cloud with an imaging instrument in the hard X-ray range (15 keV-10 MeV). The high energy flux and long-term variability of the black hole candidate LMC X-1 was measured for the first time without contamination by the nearby (∼25 ) young pulsar PSR B0540-69. We studied the accreting pulsar LMC X-4 by constraining the size of the hard X-ray emitting region (≤3 × 10 10 cm) from analysis of its eclipses and by measuring its spin period (13.497 ± 0.005 s) in the 20-40 keV band. As it was in a soft state during the first observation and possibly in an extremely low state in the second one, LMC X-3 was not detected. Thanks to the large field of view of the IBIS instrument, we could also study other sources falling serendipitously in the observed sky region around the LMC: the Galactic low mass X-ray binary EXO 0748-676, the accreting pulsar SMC X-1 in the Small Magellanic Cloud, and the Active Galactic Nucleus IRAS 04575-7537. In addition we discovered five new hard X-ray sources, two of which most likely belong to the LMC.

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Section: Lmc X-4mentioning

confidence: 97%

An INTEGRAL hard X-ray survey of the Large Magellanic Cloud

Götz¹,

Mereghetti²,

Merlini

et al. 2006

A&A

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“…About 2 days after the beginning of its observations, the pulsar switched to the on state; in another 5 days, its flux increased by a factor of about 6-8 and reached a peak (∼ 70 mCrab). The arrows in the figure indicate the switch-on and switch-off times estimated more than 20 years ago by Lang et al (1981); the switch-on time was calculated by using the ephemerides derived by these authors; the switch-off time was determined by assuming that the high state of the source lasted ∼ 60% of the entire precession period (Lang et al 1981). We see that the presumed zero phase (switch-on time) of the superorbital cycle is greatly shifted relative to the current INTEGRAL measurements.…”

mentioning

confidence: 99%

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

Tsygankov

Lutovinov

2005

Astron. Lett.

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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 ...

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“…The spin period of the neutron star is ∼ 13.5 s and the binary orbital period is ∼ 1.4 d (White 1978). This system also shows periodic superorbital modulation with a period of ∼ 30.5 d in its X-ray light curve (Lang et al 1981) caused by a precessing accretion disk with mode 0 stable warp that obscures the X-ray emission from the neutron star (Ogilvie & Dubus 2001;Clarkson et al 2003). Using the light curve collected by the All-Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE), as well as the arrival time analysis from both the GINGA and RXTE ASM data, Paul & Kitamoto (2002) found a time derivative of the superorbital period with a value ofṖ = −2 × 10 −5 s · s −1 .…”

Section: Introductionmentioning

confidence: 86%

On the Complex Variability of the Superorbital Modulation Period of LMC X-4

Hu¹,

Lin²,

Chou³

et al. 2015

Publications of The Korean Astronomical Society

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LMC X-4 is an eclipsing high-mass X-ray binary exhibiting a superorbital modulation with a period of ∼ 30.5 days. We present a detailed study of the variations of the superorbital modulation period with a time baseline of ∼ 18 years. The period determined in the light curve collected by the Monitor of All-sky X-ray Image (MAXI) significantly deviates from that observed by the All Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE). Using the data collected by RXTE/ASM, MAXI, and the Burst Alert Telescope (BAT) onboard Swift, we found a significant period derivative,Ṗ = (2.08 ± 0.12) × 10 −5 . Furthermore, the O-C residual shows complex short-term variations indicating that the superorbital modulation of LMC X-4 exhibits complicated unstable behaviors. In addition, we used archive data collected by the Proportional Counter Array (PCA) on RXTE to estimate the orbital and spin parameters. The detected pulse frequencies obtained in small time segments were fitted with a circular orbital Doppler shift model. In addition to orbital parameters and spin frequency for each observation, we found a spin frequency derivative ofν = (6.482 ± 0.011) × 10 −13 Hz · s −1 . More precise orbital and spin parameters will be evaluated by the pulse arrival time delay technique in the future.

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Discovery of a 30.5 day periodicity in LMC X-4

Cited by 94 publications

References 0 publications

An INTEGRAL hard X-ray survey of the Large Magellanic Cloud

An INTEGRAL hard X-ray survey of the Large Magellanic Cloud

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

On the Complex Variability of the Superorbital Modulation Period of LMC X-4

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