Optical clues to the nature of Hercules X-1/HZ Herculis

Gerend, D.; Boynton, P. E.

doi:10.1086/154751

Cited by 179 publications

(166 citation statements)

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“…Díaz Trigo et al (2009) explained the appearance and disappearance of dips in XB 1254−690 as well as the changes in the optical emission by invoking a precessing warped disc, similar to the one in Her X-1 (Gerend & Boynton 1976). A warped disc in GX 13+1 together with a high inclination for the system would explain both the detection of a modulation in X-rays and the fact that the structure causing it is not phase-locked.…”

Section: Orbital Period Dependence Of the Windmentioning

confidence: 95%

XMM-Newtonobservations of GX 13 + 1: correlation between photoionised absorption and broad line emission

Trigo¹,

Sidoli

Boirin

et al. 2012

A&A

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We analysed data from five XMM-Newton observations of GX 13+1 to investigate the variability of the photo-ionised absorber in this source. We fitted EPIC and RGS spectra obtained from the "least-variable" intervals with a model consisting of disc-blackbody and blackbody components together with a Gaussian emission feature at ∼6.55-6.7 keV modified by absorption due to cold and photoionised material. We found a significant correlation between the hard, ∼6-10 keV, flux, the ionisation and column density of the absorber and the equivalent width of the broad iron line. We interpret the correlation in a scenario in which a disc wind is thermally driven at large, ∼10 10 cm, radii and the broad line results from reprocessed emission in the wind and/or hot atmosphere. The breadth of the emission line is naturally explained by a combination of scattering, recombination and fluorescence processes. We attribute the variations in the absorption and emission along the orbital period to the view of different parts of the wind, possibly located at slightly different inclination angles. We constrain the inclination of GX 13+1 to be between 60 and 80 • from the strong absorption in the line of sight, which obscures up to 80% of the total emission in one observation, and the absence of eclipses. We conclude that either a disc wind and/or a hot atmosphere can explain the current observations of narrow absorption and broad iron emission features in neutron star low-mass X-ray binaries as a class.

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Section: Orbital Period Dependence Of the Windmentioning

confidence: 95%

XMM-Newtonobservations of GX 13 + 1: correlation between photoionised absorption and broad line emission

Trigo¹,

Sidoli

Boirin

et al. 2012

A&A

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“…The 35-day modulation of the X-ray flux is generally explained by the precession of the accretion disk, which quasiregularly blocks the line of sight to the X-ray emitting regions near the magnetic poles of the neutron star (Gerend & Boynton 1976;Schandl & Meyer 1994). The resulting clock, however, is irregular, showing deviations from regularity of up to ±10 d. This is generally demonstrated by the (O-C) (observed-minuscalculated) diagram (see Fig.…”

Section: Introductionmentioning

confidence: 94%

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

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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.

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“…Gerend & Boynton (1976) modeled the optical light curve by thick precessing tilted accretion disk. Afterwards.…”

Section: Introductionmentioning

confidence: 99%

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

Шакура¹,

Ketsaris²,

Прохоров³

et al. 1998

Monthly Notices RAS

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An analysis of the publically available RXTE archive on Her X-1 including data on 23 34.85-day cycles is performed. The turn-on times for these cycles are determined. The number of cycles with a duration of 20.5 orbits has been found exceedingly larger than of shorter (20 orbits) or longer (21 orbits). A correlation between the duration of a cycle and its mean X-ray flux is noted. The mean X-ray light curve shows a very distinct short-on state. The anomalous X-ray absorption dip is found during the first orbit after the turn-on in the main-on state for the cycles starting near the binary phase 0.25, while is present during two successive orbits in the low-on state. The post-eclipse recovery feature have not been found in the main-on state but appears at least for two orbits during the low-on state. The pre-eclipse dips are present both in main-on and low-on state and demonstrate the behaviour as in early observations. The comparison of durations of the main-on and short-on states enabled us to constrain the accretion disk semi-thickness and its inclination to the orbital plane.

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Optical clues to the nature of Hercules X-1/HZ Herculis

Cited by 179 publications

References 0 publications

XMM-Newtonobservations of GX 13 + 1: correlation between photoionised absorption and broad line emission

XMM-Newtonobservations of GX 13 + 1: correlation between photoionised absorption and broad line emission

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

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

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