Discovery of X-ray pulsations in SMC X-1

Lucke, R. L.; Yentis, D.; Friedman, H.; Fritz, G.; Shulman, S.

doi:10.1086/182125

Cited by 47 publications

(23 citation statements)

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“…The binary nature of SMC X-1 was soon confirmed by Schreier et al (1972) who discovered periodic occultations with an orbital period of around 3.9 days. SMC X-1 also exhibits pulsations with a period of about 0.7 seconds, and the pulse fraction and shape are known to vary significantly over time (Lucke et al 1976). The existence of X-ray pulsations confirms that the accreting compact object is a neutron star.…”

Section: Introductionmentioning

confidence: 99%

Observing the Transient Pulsations of SMC X-1 with NuSTAR

Pike

Harrison²,

Bachetti

et al. 2019

ApJ

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We report on NuSTAR observations of transient pulsations in the neutron star X-ray binary SMC X-1. The transition from non-pulsing to pulsing states was not accompanied by a large change in flux. Instead, both pulsing and non-pulsing states were observed in a single observation during the low-flux super-orbital state. During the high-state, we measure a pulse period of P = 0.70117(9) s at T ref = 56145 MJD. Spectral analysis during non-pulsing and pulsing states reveals that the observations can be consistently modeled by an absorbed power law with a phenomenological cutoff resembling a Fermi-Dirac distribution, or by a partially obscured cutoff power law. The shapes of the underlying continua show little variability between epochs, while the covering fraction and column density vary between super-orbital states. The strength of pulsations also varies, leading us to infer that the absence and reemergence of pulsations are related to changing obscuration, such as by a warped accretion disk. SMC X-1 is accreting near or above its Eddington limit, reaching an unabsorbed X-ray luminosity of L X (2 − 10 keV) ≈ 5 × 10 38 erg s −1 . This suggests that SMC X-1 may be a useful local analog to ultraluminous X-ray pulsars (ULXPs), which likewise exhibit strong variability in their pulsed fractions, as well as flux variability on similar timescales. In particular, the gradual pulse turn-on which has been observed in M82 X-2 is similar to the behavior we observe in SMC X-1. Thus we propose that pulse fraction variability of ULXPs may also be due to variable obscuration.

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Section: Introductionmentioning

confidence: 99%

Observing the Transient Pulsations of SMC X-1 with NuSTAR

Pike

Harrison²,

Bachetti

et al. 2019

ApJ

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“…SMC X‐1 also discovered using Uhuru (Leong et al 1971) consists of a neutron star of spin period 0.71 s (Lucke et al 1976) and a young B0 super giant companion (Webster et al 1972; Liller 1973). There are clear X‐ray eclipses which occur once every orbital period of 3.892 ddays (Schreier et al 1972b).…”

Section: Introductionmentioning

confidence: 99%

Effect of pulse profile variations on measurement of eccentricity in orbits of Cen X-3 and SMC X-1

Raichur¹,

Paul²

2010

Monthly Notices of the Royal Astronomical Society

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It has long been argued that better timing precision allowed by satellites like Rossi X‐ray Timing Explorer (RXTE) will allow us to measure the orbital eccentricity and the angle of periastron of some of the bright persistent high‐mass X‐ray binaries (HMXBs) and hence a possible measurement of apsidal motion in these system. Measuring the rate of apsidal motion allows one to estimate the apsidal motion constant of the mass losing companion star and hence allows for the direct testing of the stellar structure models for these giant stars present in the HMXBs. In the present paper, we use the archival RXTE data of two bright persistent sources, namely Cen X‐3 and SMC X‐1, to measure the very small orbital eccentricity and the angle of periastron. We find that the small variations in the pulse profiles of these sources, rather than the intrinsic time resolution provided by RXTE, limit the accuracy with which we can measure arrival time of the pulses from these sources. This influences the accuracy with which one can measure the orbital parameters, especially the very small eccentricity and the angle of periastron in these sources. The observations of SMC X‐1 in the year 2000 were taken during the high‐flux state of the source and we could determine the orbital eccentricity and ω using this data set.

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“…The high‐mass X‐ray binary (HMXB) system SMC X‐1/Sk 160 consists of a neutron star with a mass of ∼1.06 M ⊙ (van der Meer et al 2007) and a spin period of 0.71 s (Lucke et al 1976), accreting from the B0I star Sk 160 with a mass of ∼17.2 M ⊙ (Reynolds et al 1993). Orbital period of the system is ∼3.9 d (Schreier et al 1972).…”

Section: Introductionmentioning

confidence: 99%

Analysis ofRXTE-PCA Observations of SMC X-1

İnam

Baykal

Beklen

2010

Monthly Notices of the Royal Astronomical Society

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We present timing and spectral analysis of Rossi X‐ray Timing Explorer‐Proportional Counter Array observations of SMC X‐1 between 1996 January and 2003 December. From observations around 1996 August 30 with a time‐span of ∼6 d, we obtain a precise timing solution for the source and resolve the eccentricity as 0.00089(6). We find an orbital decay rate of which is close to the previous results. Using our timing analysis and the previous studies, we construct a ∼30 yr long pulse period history of the source. We show that frequency derivative shows long‐ (i.e. more than a few years) and short‐term (i.e. order of days) fluctuations. From the spectral analysis, we found that all spectral parameters except Hydrogen column density showed no significant variation with time and X‐ray flux. Hydrogen column density is found to be higher as X‐ray flux gets lower. This may be due to the increase in soft absorption when the pulsar is partially obscured as in Her X‐1 or may just be an artefact of the tail of a soft excess in energy spectrum.

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Discovery of X-ray pulsations in SMC X-1

Cited by 47 publications

References 0 publications

Observing the Transient Pulsations of SMC X-1 with NuSTAR

Observing the Transient Pulsations of SMC X-1 with NuSTAR

Effect of pulse profile variations on measurement of eccentricity in orbits of Cen X-3 and SMC X-1

Analysis ofRXTE-PCA Observations of SMC X-1

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