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

Iaria, R.; Salvo, T. Di; Robba, N. R.; Burderi, L.

doi:10.1086/338507

Cited by 21 publications

(47 citation statements)

References 25 publications

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“…The data at phases 0.62-0.84 are The data correspond to the phase interval 0.62-0.84 assuming the ephemeris as reported by Stewart et al (1991). The bin time is 550 s. (Iaria et al 2001a), the data at phases 0.61-0.63 (Iaria et al 2002), and the data at phases 0.62-0.84 (this paper). The bin time is 137 s. at the top right in this figure, while the data of the previous BeppoSAX observation at phases 0.61-0.63 show lower values of both the hard and the soft color.…”

Section: Observationsmentioning

confidence: 97%

“…To fit the seven spectra corresponding to the observation taken at phases 0.62-0.84, we used the Comptonization model Comptt (Titarchuk 1994), to which we added a blackbody component at low energies in agreement with Iaria et al (2002), who studied the source at similar phases. This model gave a 2 /dof of 285/202, 364/200, 330/200, 254/201, 244/199, 249/199, and 256/200, respectively, for spectra 1-7; in Table 3 we show the corresponding best-fit parameters.…”

Section: The Soft Excess Below 1 Kevmentioning

confidence: 99%

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On the Soft Excess in the X‐Ray Spectrum of Circinus X‐1: Revisitation of the Distance to Circinus X‐1

Iaria

Spanò

Salvo

et al. 2005

ApJ

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We report on a 300 ks BeppoSAX (0.12-200 keV ) observation of Circinus X-1 (Cir X-1) at phases between 0.62 and 0.84 and on a 90 ks BeppoSAX observation of Cir X-1 at phases 0.11-0.16. Using the canonical model adopted until now to fit the energy spectrum of this source, large residuals appear below 1 keV. These are well fitted using an equivalent hydrogen column of 0:66 ; 10 22 cm À2 , adding absorption edges of O vii, O viii, and Ne ix in the spectra extracted from the observation at phases 0.62-0.84 and adding absorption edges of O vii, O viii, Mg xi, and Mg xii and absorption lines of O viii and Mg xii in the spectra extracted from the observation at phases 0.11-0.16. During the observation at phases 0.62-0.84 the electron density associated with the ionized matter is $10 13 cm À3 , remaining quite constant going away from the compact object. During the observation at phases 0.11-0.16, the electron density profile varies along the distance going from $6 ; 10 13 cm À3 at $10 11 cm to $9 ; 10 10 cm À3 at $10 13 cm. The equivalent hydrogen column toward Cir X-1 is 3 times lower than the value obtained from previous models. This low value would imply that Cir X-1 is at a distance of 4.1 kpc.

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Section: Observationsmentioning

confidence: 97%

Section: The Soft Excess Below 1 Kevmentioning

confidence: 99%

On the Soft Excess in the X‐Ray Spectrum of Circinus X‐1: Revisitation of the Distance to Circinus X‐1

Iaria

Spanò

Salvo

et al. 2005

ApJ

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“…serx1_ref_mod_2 Iaria et al 2001Iaria et al , 2002, and this component may also be present in the spectrum of Ser X-1 (see Miller et al 2013). Unless it is specified otherwise, for every fit, we froze the power-law photon index to the value found by Miller et al (2013) for Ser X-1, that is 3.2.…”

Section: Nustar Spectral Analysismentioning

confidence: 99%

A re-analysis of theNuSTARandXMM-Newtonbroad-band spectrum of Serpens X-1

Matranga

Salvo

Iaria

et al. 2017

A&A

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Context. High resolution X-ray spectra of neutron star Low Mass X-ray Binaries (LMXBs) in the energy range 6.4-6.97 keV, are often characterized by the presence of Kα transition features of iron at different ionization stages. Since these lines are thought to originate by reflection of the primary Comptonization spectrum over the accretion disk, the study of these features allows us to investigate the structure of the accretion flow close to the central source. Thus, the study of these features gives us important physical information on the system parameters and geometry. Ser X-1 is a well studied LMXB which clearly shows a broad iron line. Several attempts to fit this feature as a smeared reflection feature have been performed on XMM-Newton, Suzaku, NuSTAR, and, more recently, on Chandra data, finding different results for the inner radius of the disk and other reflection or smearing parameters. For instance, Miller et al. (2013) have presented broad-band, high quality NuSTAR data of Ser X-1. Using relativistically smeared self-consistent reflection models, they find a value of R in close to 1.0 R IS CO (corresponding to 6 R g , where R g is the Gravitational radius, defined as usual2 ), and a low inclination angle of less than ∼ 10• . Aims. The aim of this paper is to probe to what extent the choice of reflection and continuum models (and uncertainties therein) can affect the conclusions about the disk parameters inferred from the reflection component. To this aim we re-analyze all the available public NuSTAR and XMM-Newton which have the best sensitivity at the iron line energy observations of Ser X-1. Ser X-1 is a well studied source, its spectrum has been observed by several instruments, and is therefore one of the best sources for this study. Methods. We use slightly different continuum and reflection models with respect to those adopted in literature for this source. In particular we fit the iron line and other reflection features with self-consistent reflection models as reflionx (with a power-law illuminating continuum modified with a high energy cutoff to mimic the shape of the incident Comptonization spectrum) and rfxconv. With these models we fit NuSTAR and XMM-Newton spectra yielding consistent spectral results. Results. Our results are in line with those already found by Miller et al. (2013) but less extreme. In particular, we find the inner disk radius at ∼ 13 R g and an inclination angle with respect to the line of sight of ∼ 27• . We conclude that, while the choice of the reflection model has little impact on the disk parameters, as soon as a self-consistent model is used, the choice of the continuum model can be important in the precise determination of the disk parameters from the reflection component. Hence broad-band X-ray spectra are highly preferable to constrain the continuum and disk parameters.

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“…A hard X-ray tail of GX 340+0 was also detected in its BeppoSAX spectra (Lavagetto et al 2004). Using the BeppoSAX observations for Cir X-1, which hosts an elliptical orbit with high eccentricity (e ∼ 0.7-0.9), Iaria et al (2001Iaria et al ( , 2002) studied its broadband spectra near the periastron (orbital phase 0) or at the orbital phases close to the apoastron (orbital phase 0.5) and detected similar hard X-ray tails with photon index ∼3.2 during the two orbital episodes. Interestingly, analyzing RXTE data, Ding et al (2006b) found orbital modulation for the hard X-ray emission of Cir X-1.…”

Section: Introductionmentioning

confidence: 99%

Hard X-ray Emission along the Z Track in GX 17 + 2

Ding

Huang

2015

J Astrophys Astron

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Abstract. Using the data from the Proportional Counter Array (PCA) and the High-Energy X-ray Timing Experiment (HEXTE) on board Rossi X-Ray Timing Explorer for Z source GX 17+2, we investigate the evolution of its PCA spectra and HEXTE spectra along a "Z" track on its hardness-intensity diagram. A hard X-ray tail is detected in the HEXTE spectra. The detected hard X-ray tails are discontinuously scattered throughout the "Z" track. The found hard tail hardens from the horizontal branch, through the normal branch, to the flaring branch in principle and it contributes ∼(20-50)% of the total flux in 20-200 keV. Our joint fitting results of the PCA+HEXTE spectra in 3-200 keV show that the portion of Comptonization in the bulk-motion Comptonization (BMC) model accounts for the hard X-ray tail, which indicates that the BMC process could be responsible for the detected hard tail. The temperature of the seed photons for BMC is ∼2.7 keV, implying that these seed photons might be emitted from the surface of the neutron star (NS) or the boundary layer between the NS and the disk and, therefore, this process could take place around the NS or in the boundary layer.

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

Cited by 21 publications

References 25 publications

On the Soft Excess in the X‐Ray Spectrum of Circinus X‐1: Revisitation of the Distance to Circinus X‐1

On the Soft Excess in the X‐Ray Spectrum of Circinus X‐1: Revisitation of the Distance to Circinus X‐1

A re-analysis of theNuSTARandXMM-Newtonbroad-band spectrum of Serpens X-1

Hard X-ray Emission along the Z Track in GX 17 + 2

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