The Discovery of a State-Dependent Hard Tail in the X-Ray Spectrum of the Luminous Z Source GX 17+2

Salvo, T. Di; Stella, L.; Robba, N. R.; Klis, M. van der; Burderi, L.; Israel, G. L.; Homan, J.; Campana, S.; Frontera, F.; Parmar, A. N.

doi:10.1086/317309

Cited by 143 publications

(196 citation statements)

References 22 publications

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“…A hard power-law tail, dominating the spectrum at energies higher than 15 keV, was also observed. A similar feature was observed in other Z-source LMXBs (GX 17]2, Di Salvo et al 2000 ;GX 349]2, Di Salvo et al 2001 ;GX 5[1, Asai et al 1994 ;Sco X-1, DÏAmico et al 2000), suggesting that Cir X-1 shows a behavior similar to that of other Z sources. Finally, a strong absorption edge at D8.4È8.7 keV, produced by highly ionized iron, was needed to Ðt the spectrum of Cir X-1.…”

Section: Introductionsupporting

confidence: 77%

Study of the Circinus X‐1 Broadband Spectrum at Orbital Phases Close to the Apoastron

Iaria

Salvo

Robba

et al. 2002

ApJ

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We report on the results of a BeppoSAX (1.8È200 keV) observation of the peculiar X-ray binary source Circinus X-1 (Cir X-1) at the orbital phases between 0.61 and 0.63. We Ðnd that three components are needed to Ðt the broadband spectrum : a blackbody component at a temperature of D0.6 keV ; a Comptonized component with a seed-photon temperature of D1.2 keV, electron temperature of D6 keV, and optical depth of D1.7 ; and a power-law component dominating the spectrum at energies higher than 20 keV. We interpret the blackbody as the emission from the accretion disk, while the Comptonized component probably comes from a corona surrounding the inner part of the system. This spectrum is di †erent from that observed at the periastron (in our previous work) because of the presence of the blackbody component. We discuss the implications of this di †erence and the presence of the power-law component.

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Section: Introductionsupporting

confidence: 77%

Study of the Circinus X‐1 Broadband Spectrum at Orbital Phases Close to the Apoastron

Iaria

Salvo

Robba

et al. 2002

ApJ

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“…In Aquila X -1 the X-ray luminosity throughout the CD, i.e., from the left of the banana state to the right of the extreme island state is about three orders of magnitude. In Z sources, luminosity changes are typically less than a factor of 2 (di Salvo et al 2000Salvo et al , 2001.…”

Section: Is Aquila X -1 a Z Source?mentioning

confidence: 99%

Timing Properties and Spectral States in Aquila X‐1

Reig¹,

Straaten²,

Klis³

2004

ApJ

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We have analyzed five X-ray outbursts of the neutron-star soft X-ray transient Aquila X -1 and investigated the timing properties of the source in correlation with its spectral states as defined by different positions in the color-color and hardness-intensity diagrams. The hard color and the source count rate serve as the distinguishing parameters giving rise to three spectral states: a low-intensity hard state, an intermediate state and a high-intensity soft state. These states are respectively identified with the extreme island, island and banana states that characterize the atoll sources. The large amount of data analyzed allowed us to perform for the first time a detailed timing analysis of the extreme island state. Differences in the aperiodic variability between the rise and the decay of the X-ray outbursts are found in this state: at the same place in the color-color diagram, during the rise the source exhibits more power at low frequencies ( < ∼ 1 Hz), whereas during the decay the source is more variable at high frequencies ( > ∼ 100 Hz). The very-low frequency noise that characterizes the banana-state power spectra below 1 Hz cannot be described in terms of a single power law but a two-component model is required. In two outbursts a new 6-10 Hz QPO has been discovered and tentatively identified with the normal/flaring branch-like oscillation observed only at the highest inferred mass accretion rates. We have compared the spectral and timing properties of Aquila X -1 with those of other atoll and Z sources. Our results argue against a unification scheme for these two types of neutron-star X-ray binaries.

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“…However in the atoll sources in their hard state the luminosity of the  component is less than about 20% with respect to their total luminosity, while in our case the  contributes to more than 50% of the total luminosity. A strong contribution of the  component to the total X-ray luminosity is instead typical of Z-sources (see, e.g., Di Salvo et al 2000). This "anomaly" of the RB spectrum with respect to that of the other atoll sources could however be related to the particular, and still not well understood, physical environment of the source (perhaps the "propellereffect" caused by the magnetic field of the neutron star).…”

Section: Discussionmentioning

confidence: 99%

The discovery of hard X-ray emission in the persistent flux of the Rapid Burster

Falanga¹,

Farinelli

Goldoni³

et al. 2004

A&A

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Abstract.We report the first detection with INTEGRAL of persistent hard X-ray emission (20 to 100 keV) from the Rapid Burster (MXB 1730-335), and describe its full spectrum from 3 to 100 keV. The source was detected on February/March 2003 during one of its recurrent outbursts. The source was clearly detected with a high signal to noise ratio during the single pointings and is well distinguished from the neighboring source GX 354-0. The 3-100 keV X-ray spectrum of the persistent emission is well described by a two-component model consisting of a blackbody plus a power-law with photon index ∼2.4. The estimated luminosity was ∼8.5 × 10 36 erg s −1 in the 3-20 keV energy band and ∼1.3 × 10 36 erg s −1 in the 20-100 keV energy range, for a distance of 8 kpc.

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The Discovery of a State-Dependent Hard Tail in the X-Ray Spectrum of the Luminous Z Source GX 17+2

Cited by 143 publications

References 22 publications

Study of the Circinus X‐1 Broadband Spectrum at Orbital Phases Close to the Apoastron

Study of the Circinus X‐1 Broadband Spectrum at Orbital Phases Close to the Apoastron

Timing Properties and Spectral States in Aquila X‐1

The discovery of hard X-ray emission in the persistent flux of the Rapid Burster

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