RXTE highlights of the 34.85-day cycle of Her X-1

Шакура, Н. И.; Ketsaris, N. A.; Прохоров, М. Е.; Постнов, К. А.

doi:10.1046/j.1365-8711.1998.01974.x

Cited by 35 publications

(31 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, our results are insensitive to the choice of uncertainties. Whilst this is a very rough method, the results agree surprisingly well with the more detailed analysis (basically a template fitting method) of Shakura et al (1998). Next a linear ephemeris was fit to the times of the main-ons that occurred before the anomalous lowstate to give a mean 35 day cycle time of 34.8 day, consistent with the model of Staubert et al (1983) where it is proposed that the mean period is 20.5 times the orbital period, i.e., 34.85 day and that the observed on-states can fluctuate around this value by 0 or ± 1 2 orbital cycles.…”

Section: Day Turn-on Timesupporting

confidence: 68%

A BeppoSAX observation of Her X-1 during the first main-on after an anomalous low-state: Evidence for rapid spin-down

Oosterbroek

Parmar

Orlandini³

et al. 2001

A&A

View full text Add to dashboard Cite

Abstract.Results of a BeppoSAX observation of Her X-1 in 2000 October during the first main-on state after the longest recorded anomalous low-state are presented. The 0.1-30 keV spectrum, light curve and pulse profile are all consistent with those measured during previous main on-states, indicating that Her X-1 has resumed its regular 35 day cycle with similar on-state properties as before. However, from a comparison of the measured pulse period with that obtained close to the start of the anomalous low-state, it is evident that Her X-1 continued to spin-down strongly during the anomalous low-state such that the pulse period has returned to a similar value as ∼15 years ago. Additionally, the occurrence time of the main-on states after the end of the anomalous low-state indicate that a change in the length, or phasing, of the 35-day cycle occurred during the anomalous low-state.

show abstract

Section: Day Turn-on Timesupporting

confidence: 68%

A BeppoSAX observation of Her X-1 during the first main-on after an anomalous low-state: Evidence for rapid spin-down

Oosterbroek

Parmar

Orlandini³

et al. 2001

A&A

View full text Add to dashboard Cite

show abstract

“…For example, the peaks of each superorbital cycle have a number of prominent dips (see Fig. 4), which appear to be akin to the ''preeclipse dips'' seen in the long-term X-ray light curves of Her X-1 (Shakura et al 1998;Stelzer et al 1999;Klochkov et al 2005). To further reduce the inherent noise in the ASM light curves of SMC X-1, we applied a simple Gaussian smoothing to the unbinned ASM data via a fast Fourier transform (FFT ) 7 with a smoothing scale of 16 data bins ($2.5 days on average).…”

Section: Defining the Superorbital Ephemerismentioning

confidence: 98%

Tracking the Orbital and Superorbital Periods of SMC X‐1

Trowbridge¹,

Nowak

Wilms³

2007

ApJ

View full text Add to dashboard Cite

The high-mass X-ray binary ( HMXB) SMC X-1 demonstrates an orbital variation of $3.89 days and a superorbital variation with an average length of $55 days. As we show here, however, the length of the superorbital cycle varies by almost a factor of 2, even across adjacent cycles. To study both the orbital and superorbital variation, we utilize light curves from the Rossi X-Ray Timing Explorer All-Sky Monitor (RXTE ASM ). We employ the orbital ephemeris from P. Wojdowski et al. to obtain the average orbital profile, and we show that this profile exhibits complex modulation during noneclipse phases. In addition, a very interesting ''bounceback'' in X-ray count rate is seen during midorbital eclipse phases, with a softening of the emission during these periods. This bounceback has not been previously identified in pointed observations. We then define a superorbital ephemeris (the phase of the superorbital cycle as a function of date) based on the ASM light curve and analyze the trend and distribution of superorbital cycle lengths. SMC X-1 exhibits a bimodal distribution of these lengths, similar to what has been observed in other systems (e.g., Her X-1), but with more dramatic changes in cycle length. There is some hint, but not conclusive evidence, for a dependence of the superorbital cycle length on the underlying orbital period, as has been observed previously for Her X-1 and Cyg X-2. Using our superorbital ephemeris, we are also able to create an average superorbital profile over the 71 observed cycles, for which we witness overall hardening of the spectrum during low count rate times. We combine the orbital and superorbital ephemerides to study the correlation between the orbital and superorbital variations in the system, but find that the ASM light curve provides insufficient statistics to draw any definitive conclusions on possible correlations.

show abstract

“…Trümper et al (1986) had suggested that the systematic variation in pulse shape is due to free precession of the neutron star: the viewing angle towards the X-ray emitting regions of the neutron star varies with the phase of the neutron star precession. Shakura et al (1998) applied a model of a precessing triaxial shape to pulse profiles of Her X-1 observed by HEAO-1, and Ketsaris et al (2000) did so for profiles observed by RXTE/PCA. Using all observations by RXTE from 1996 until 2005 we have verified that the shape of the pulse profiles is reproduced every ∼35 days.…”

Section: Pulse Profile Variationsmentioning

confidence: 99%

Variable pulse profiles of Hercules X-1 repeating with the same irregular 35 d clock as the turn-ons

Staubert¹,

Klochkov²,

Vasco³

et al. 2013

A&A

View full text Add to dashboard Cite

The accreting X-ray pulsar Her X-1 shows two types of long-term variations, both with periods of ∼35 days: 1) turn-on cycles, a modulation of the flux, with a ten-day long main-on and a five-day long short-on, separated by two off-states, and 2) a systematic variation in the shape of the 1.24 s pulse profile. While there is general consensus that the flux modulation is due to variable shading of the X-ray emitting regions on the surface of the neutron star by the precessing accretion disk, the physical reason for the variation in the pulse profiles has remained controversial. Following the suggestion that free precession of the neutron star may be responsible for the variation in the pulse profiles, we developed a physical model of strong feedback interaction between the neutron star and the accretion disk in order to explain the seemingly identical values for the periods of the two types of variations, which were found to be in basic synchronization. In a deep analysis of pulse profiles observed by several different satellites over the last three decades we now find that the clock behind the pulse profile variations shows exactly the same erratic behavior as the turn-on clock, even on short time scales (a few 35 d cycles), suggesting that there may in fact be only one 35 d clock in the system. If this is true, it raises serious questions with respect to the idea of free precession of the neutron star, namely how the neutron star can change its precessional period every few years by up to 2.5% and how the feedback can be so strong, such that these changes can be transmitted to the accretion disk on rather short time scales.

show abstract

RXTE highlights of the 34.85-day cycle of Her X-1

Cited by 35 publications

References 22 publications

A BeppoSAX observation of Her X-1 during the first main-on after an anomalous low-state: Evidence for rapid spin-down

A BeppoSAX observation of Her X-1 during the first main-on after an anomalous low-state: Evidence for rapid spin-down

Tracking the Orbital and Superorbital Periods of SMC X‐1

Variable pulse profiles of Hercules X-1 repeating with the same irregular 35 d clock as the turn-ons

Contact Info

Product

Resources

About