On the Constancy of the Photon Index of X-Ray Spectra of 4u 1728-34 Through All Spectral States

Seifina, Elena; Titarchuk, Lev

doi:10.1088/0004-637x/738/2/128

Cited by 30 publications

(36 citation statements)

References 46 publications

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“…For instance, Farinelli & Titarchuk (2011) measured the power-law index and the electron temperature kTe of the Comptonising component in the neutron star LMXBs Sco X-1, GX 349+2, X 1658−298, 1E 1724−3045, GX 17+2, Cyg X−2, GX 340+0, GX 3+1, and GS 1826−238, and found that the power-law energy index (Γ − 1 in the nthcomp component) remains more or less constant at around 1±0.2. Using RXTE and BeppoSAX observations, Seifina & Titarchuk (2011 showed that in 4U 1728−34 and GX 3+1, the power-law index also remains almost constant as the temperature of the corona changes dramatically. Recently, Titarchuk et al (2013) found that in another neutron star binary, 4U 1820−30, the power-law index remains almost constant for different source states.…”

Section: Discussionmentioning

confidence: 99%

Iron-line and continuum variations in the XMM–Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636−53

Lyu

Méndez

Sanna

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five Suzaku observations to study the continuum spectrum and the iron emission line in the neutron-star low-mass X-ray binary 4U 1636−53. We modelled the spectra with two thermal components (representing the accretion disc and boundary layer), a Comptonised component (representing a hot corona), and either a Gaussian or a relativistic line component to model an iron emission line at ∼ 6.5 keV. For the relativistic line component we used either the diskline, laor or kyrline model, the latter for three different values of the spin parameter. The fitting results for the continuum are consistent with the standard truncated disc scenario. We also find that the flux and equivalent width of the iron line first increase and then decrease as the flux of the Comptonised component increases. This could be explained either by changes in the ionisation state of the accretion disc where the line is produced by reflection, or by light bending of the emission from the Comptonised component if the height at which this component is produced changes with mass accretion rate.

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Section: Discussionmentioning

confidence: 99%

Iron-line and continuum variations in the XMM–Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636−53

Lyu

Méndez

Sanna

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…As one can see from this Figure, HID for 4U 1630-47 exhibits two separate branches related to the hard spectral states (vertical branch) and to the sof t states (horizontal branch), whereas all NS sources (except 4U 1728-34) show only the soft horizontal branch elongated close to the soft branch of 4U 1630-47. A unique stability (or quasi-constancy) of the hardness ratio for NSs versus the 3 − 10 keV flux is an observational demonstration for the stability of the photon index Γ established for a number of NS sources (see Farinelli & Titarchuk 2011, Seifina & Titarchuk 2011and Seifina et al 2013). This hardness ratio vs the 3 − 10 keV flux provides a unique diagnostics for the nature of a given compact object.…”

Section: Overall Pattern Of X-ray Propertiesmentioning

confidence: 96%

Black Hole Mass Determination in the X-Ray Binary 4u 1630-47: Scaling of Spectral and Variability Characteristics

Seifina¹,

Titarchuk

Shaposhnikov

2014

ApJ

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We present the results of a comprehensive investigation on the evolution of spectral and timing properties of the Galactic black hole candidate 4U 1630-47 during its spectral transitions. In particular, we show how a scaling of the correlation of the photon index of the Comptonized spectral component Γ with low frequency of quasi-periodic oscillations (QPO), ν L and mass accretion rate, M can be applied to the black hole mass and the inclination angle estimates. We analyze the transition episodes observed with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. We find that the broadband X-ray energy spectra of 4U 1630-47 during all spectral states can be modeled by a combination of a thermal component, a Comptonized component and a red-skewed iron line component. We also establish that Γ monotonically increases during transition from the low-hard state to the high-soft state and then saturates for high mass accretion rates. The index saturation levels vary for different transition episodes. Correlations of Γ versus ν L also shows saturation at Γ ∼ 3. Γ −Ṁ and Γ − ν L correlations with their index saturation revealed in 4U 1630-47 are similar to those established in a number of other BHCs and can be considered as an observational evidence for the presence of a black hole in these sources. The scaling technique, which relies on XTE J1550-564, GRO 1655-40 and H 1743-322 as reference sources, allows us to evaluate a black hole mass in 4U 1630-47 yielding M BH ∼ 10 ± 0.1 solar masses, and to constrain the inclination angle of i < ∼ 70 • .

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“…Note that in a case of the two-Comptb model, we deal with two seed-photon temperatures, in which a low value of the temperature cannot be determined, because the PCA low-energy threshold (∼ 3 keV) is above the peak of the disk seed-photon blackbody which temperature, typically < ∼ 0.7 keV in LMXBs, [see Barret 2001, Seifina & Titarchuk (2011, Seifina & Titarchuk (2012), Seifina, Titarchuk & Frontera (2013)]. The results of these fits to the two-Comptb model are reported in Table 2.…”

Section: Spectral Analysismentioning

confidence: 99%

X-Ray Spectral and Timing Behavior of Scorpius X-1. Spectral Hardening During the Flaring Branch

Titarchuk

Seifina²,

Shrader

2014

ApJ

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We present an analysis of the spectral and timing properties of X-ray emission from the Z-source Sco X-1 during its evolution between the Horizontal (HB) and Flaring (FB) branches observed with the Rossi X-ray Timing Explorer during the 1996 -2002 period. We find that the broad-band (3 -250 keV) energy spectra during all spectral states can be adequately reproduced by a model, consisting of two Comptonized components and an iron-line. We suggest that the seed photons of kT s1 < ∼ 0.7 keV coming from the disk and of temperature kT s2 < ∼ 1.8 keV coming from the neutron star (NS) are each upscattered by hot electrons of a "Compton cloud" (herein Comptb1 and Comptb2 components respectively with which are associated similarly subscripted parameters). The photon power-law index Γ 2 is almost constant (Γ 2 ∼ 2) for all spectral states. In turn, Γ 1 demonstrates a twophase behavior with the spectral state: Γ 1 is quasi-constant at the level Γ 1 ∼ 2 for the HB−NB and Γ 1 is less than 2, namely in the range of 1.3 < Γ 1 < 2, when source traces the FB. We also detect a decrease kT s2 from 1.8 keV to 0.7 keV during the FB. We interpret this apparent quasi-stability of the indices during the HB−NB in the framework of the model in which the spectrum is determined by the Comptonized thermal components. This established for the Comptonized spectral components of the Z-source Sco X-1 is similar to that was previously -2found in the atoll sources 4U 1728-34, GX 3+1 and 4U 1820-30 and the Z-source GX 340+0 through all spectral states. However we interpret the index reduction phase detected during the FB in Sco X-1 within the framework of a model in which the spectrum at the FB is determined by high radiation pressure from the NS surface.

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On the Constancy of the Photon Index of X-Ray Spectra of 4u 1728-34 Through All Spectral States

Cited by 30 publications

References 46 publications

Iron-line and continuum variations in the XMM–Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636−53

Iron-line and continuum variations in the XMM–Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636−53

Black Hole Mass Determination in the X-Ray Binary 4u 1630-47: Scaling of Spectral and Variability Characteristics

X-Ray Spectral and Timing Behavior of Scorpius X-1. Spectral Hardening During the Flaring Branch

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