Short-term time variability of Cygnus X-1. II

Sutherland, P. G.; Weisskopf, Miriam; Kahn, S. M.

doi:10.1086/155867

Cited by 39 publications

(15 citation statements)

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“…As suggested by BH90a (see also Meekins et al 1984), the shape of the power spectrum of Cyg X-1 in the low state can be qualitatively interpreted with a light curve consisting of a superposition of randomly distributed shots with a range of lifetimes, an extension of the standard "shot-noise" model (Terrell 1972, Sutherland, Weisskopf, & Kahn 1978. The higher frequency cutoff at higher count rates (which we interpret as an increase in accretion rate) indicates that in the 1996 May data the longer living shots disappear and only the fastest ones survive.…”

Section: Discussionmentioning

confidence: 86%

An Intermediate State of Cygnus X-1

Belloni

Méndez

Klis

et al. 1996

The Astrophysical Journal

371

808

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Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. VAN PARADIJS 1, 5 Received 1996 July 11; accepted 1996 September 5 ABSTRACT We report RXTE͞PCA observations of the black hole candidate Cygnus X-1. In 1996 February the source was in its usual "low" state. In three observations during 1996 May the source was on average brighter by a factor of 2 and showed less rapid variability and a softer energy spectrum. However, the observations indicate that Cyg X-1 did not enter a high state like the one observed in black hole transients. Flux, variability, and spectral shape suggest instead that the source was in an "intermediate" state similar to what has been observed in GS 1124Ϫ68 and GX 339Ϫ4. Perhaps also the state transitions of Cyg X-1 observed in the 1970s were not to a high state but to this intermediate state.

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Section: Discussionmentioning

confidence: 86%

An Intermediate State of Cygnus X-1

Belloni

Méndez

Klis

et al. 1996

The Astrophysical Journal

371

808

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“…In this model a events per time interval each rise to amplitude h and then exponentially decay away with time scale r. Thus using I n ahr and aY n 02 r/2 we construct We set N = ar which represents the number of "simultaneous" events taking place. If we assume that r is longer than the smallest bin size we used (see Sutherland, Weisskopf, and Kahn 1978 Appendix A, to see how a 2 is a function of bin size) and that a is greater than one shot per day, then we can use 8 from Table 1. For NGC 6814 N -10 which says that at any one time on the averge 10 clouds dominate most of the X-ray flux.…”

Section: Shot Noisementioning

confidence: 99%

The absence of rapid X-ray variability in active galaxies

Tennant¹,

Mushotzky²

1983

ApJ

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We have searched for variations on time scales ranging from minutes to several hours in the X-ray flux from 54 observations of 38 active galaxies.Our sample is composed mostly of Seyfert I galaxies but also includes radio galaxies, NELG's, BL Lacs and 3C 273. Only NGC 6814 varied or time scales as short as 100 sec. No other source was observed to vary with a time scale of less than 12 hours. We conclude that large-amplitude short-term variations are not a characteristic of the X-ray emission from active galaxies. Upper limits on a I /I ranged from 2% for Cen A, 5% for NGC 4151, to -20% for sources giving 1 ct/sec in our detector. Three objects NGC 3227, NGC 4151 and MCG 5-23-16 show variability consistent with a time scale of -1 day.We consider ways to reconcile the rapid variability seen for NGC 6814 (and NGC 4051) with the general stability observed for the other objects. If the lack of variability is due to the growth of a new, constant source of soft photons (such as thermal re-radiation from dust) then the X-ray plasma must be 2 much larger than the size implied by the variations seen in NGC 6814. Other possibilities are that the "originally lumpy" accretion flow stablizes or that NGC 6814 is different from other galaxies. Subject headings --Galaxies: nuclei -Galaxies: Seyfert -X-ray: sources J i From a dissertation to be submitted to Graduate School, University of Maryland, by Allyn F. Tennant in partial fulfillment of the requirements for the Ph.D. degree in Physics.

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“…The studies of temporal properties of the rapid variability in the hard X-rays should be a hopeful method of understanding the properties of the compact object. In the low state (LS), the variability of X-rays could be described approximately as the superposition of individual shots (Terrel 1972 ;Oda 1977 ;Sutherland, Weisskopf, & Kahn 1978 ;Miyamoto et al 1988 ;Miyamoto et al 1992). The properties of the rapid Ñuctuation or shot had been studied from the autocorrelation function (ACF) and the power density spectrum (PDS) based on the supposition of randomly occurring shots (Nolan et al 1981 ;Lochner, Swank, & Szymkowiak 1991).…”

Section: Introductionmentioning

confidence: 99%

X‐Ray Shots of Cygnus X‐1

Feng

Chen

1999

ApJ

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X-ray shots of Cyg X-1 in di †erent energy bands and spectral states have been studied with proportional counter array (PCA)/Rossi X-Ray T iming Explorer (RXT E) observations. The detailed shot structure is obtained by superposing many shots with 1 ms time bin through aligning their peaks with an improved algorithm. In general, the shots are composed of a slow rise and fast decay. The shot structures in the di †erent states are di †erent. The duration of a shot in the high state is shorter than that in the low and transition states. The shot proÐle in the high-energy band is more asymmetric and narrower than that in the low-energy band. The average hardness of a shot is lower than that of steady emission in the transition and low states but higher than that in the high state. The time lags between the shots in higher and lower energy bands have been found in the di †erent states. In transition states, the time lag is largest among the di †erent states of Cyg X-1, and it is smallest in the low state. The implications of the observed shot features for shot models are discussed.

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Short-term time variability of Cygnus X-1. II

Cited by 39 publications

References 0 publications

An Intermediate State of Cygnus X-1

An Intermediate State of Cygnus X-1

The absence of rapid X-ray variability in active galaxies

X‐Ray Shots of Cygnus X‐1

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