Circinus X-1 - X-ray observations with SAS 3

Dower, R. G.; Bradt, H.; Morgan, E.

doi:10.1086/160334

Cited by 25 publications

(16 citation statements)

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“…1516-569/Cir X-1 For some time Circinus X-1 has been considered a black-hole candidate because its erratic intensity variations were somewhat similar to those of Cygnus X-1 (see e.g. Dower et al 1982, for a review of much of the older literature on Cir X-I). Kaluzienski et al (1976) discovered that the large variability of Cir X-1 contained a periodic component, in the form of flares which were terminated by a very sudden intensity drop (in some cases within a minute) to a low-intensity state.…”

Section: -314/cen X-4mentioning

confidence: 99%

X-ray bursts

1993

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Section: -314/cen X-4mentioning

confidence: 99%

X-ray bursts

1993

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“…Further type I bursts have not been observed from Cir X-1 since the EX-OSAT discovery, possibly because the source intensity has been higher during subsequent observations. No coherent pulsations, which would be expected to be present if the compact star is a strongly magnetized neutron star, have been detected (Dower, Bradt, & Morgan 1982;Vaughan et al 1994).…”

Section: Introductionmentioning

confidence: 99%

The Complete “Z” Track of Circinus X‐1

Shirey¹,

Bradt²,

Levine³

1999

ApJ

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We carried out an extensive Rossi X-ray Timing Explorer campaign, in 1997 June, to study Circinus X-1 during the active portion of its 16.55-d intensity cycle. The observations spanned 10 days, including 56% coverage for 7 d, and allowed us to find time segments which clearly demonstrate continuous evolution along the horizontal, normal, and flaring branches (HB/NB/FB) of a Z-source low-mass X-ray binary. These results confirm and extend the behavior we inferred from earlier observations. Here we study the continuous evolution of the Fourier power spectra and the energy spectra around the complete hardness-intensity track.A narrow quasi-periodic oscillation (QPO) peak, previously observed in the power spectra at 1.3-32 Hz, increases in frequency from 12 Hz to 25 Hz moving down a vertical extension of the horizontal branch in the hardness-intensity diagram. These horizontal branch QPOs (HBOs) occur near 30 Hz and fade in strength on the horizontal portion of the HB, while a broad peak in the power spectrum arises near 4 Hz. This peak becomes much more prominent along the normal branch and remains near 4 Hz (the normal branch QPOs, or NBOs). On the flaring branch, neither QPO is present and the power spectrum is dominated by very low frequency noise. We also found that each branch of the spectral track is associated with a specific type of evolution of the energy spectrum. We explored various models for the energy spectrum and parameterized the evolution of the spectrum in terms of a two-component model consisting of a multi-temperature "disk blackbody" and a higher-temperature (∼2 keV) blackbody. We also show that an unusual line-or edge-like feature occurs at about 10 keV in energy spectra from the flaring branch and lower normal branch. This unusual feature is very similar to one seen on the FB and lower NB of the Z source GX 5−1.

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“…For some time Cir X-1 was considered as a black-hole candidate because of its rapid erratic X-ray flux variations (see Dower et al 1982 for a review of the older literature on Cir X-1), but the detection of type I X-ray bursts, caused by thermonuclear flashes on the surface of the neutron star (Tennant, Fabian & Shafer 1986a, Tennant, Fabian & Shafer 1986b) established that Cir X-1 is an accreting neutron star. In the 1970s the periodic radio flares of Cir X-1 peaked at > 1 Jy; since then its radio flux has decreased dramatically, and in the past 10 yr it has rarely been detected at a level above 50 mJy (e.g.…”

Section: Introductionmentioning

confidence: 99%

An Asymmetric Arcsecond Radio Jet from Circinus X-1

Fender

Spencer

Tzioumis

et al. 1998

The Astrophysical Journal

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In observations with the Australia Telescope Compact Array we have resolved the radio counterpart of the unusual X-ray binary Cir X-1 into an asymmetric extended structure on arcsecond scales. In order to quantify the asymmetry we have redetermined as accurately as possible both the optical and radio coordinates of the source. The extended emission can be understood as a compact, absorbed core at the location of the X-ray binary, and extended emission up to 2 arcsec to the southeast of the core. The arcsec-scale extended emission aligns with the larger, more symmetric arcmin-scale collimated structures in the surrounding synchrotron nebula. This suggests that the transport of mass and/or energy from the X-ray binary to the synchroton nebula is occurring via the arcsec-scale structures. The ratio of extended flux from the southeast to that from the northwest of the core is at least 2:1. Interpreted as relativistic aberration of an intrinsically symmetric jet from the source, this implies a minimum outflow velocity of 0.1 c. Alternatively, the emission may be intrinsically asymmetric, perhaps as a result of the high space velocity of the system.

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Circinus X-1 - X-ray observations with SAS 3

Cited by 25 publications

References 0 publications

X-ray bursts

X-ray bursts

The Complete “Z” Track of Circinus X‐1

An Asymmetric Arcsecond Radio Jet from Circinus X-1

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