Stability of the photon indices in Z-source GX 340+0 for spectral states

Abstract

We show an analysis of the spectral and timing properties of X-ray radiation from Z-source during its evolutions when the electron temperature of the Transition Layer (TL) kT_e monotonically decreases from 21 to 3 keV. We analyze episodes observed with the BeppoSAX and Rossi X-ray Timing Explorer (RXTE). We reveal that the X-ray broad-band energy spectra during all spectral states can be reproduced by a {physical} model, composed of a soft blackbody component, {two Comptonized components (both due to the presence of that TL that up-scatters both seed photons of T_{s1}<1 keV coming from the disk (first component, Comptb1), and seed photons of temperature T_{s2}<1.5 keV coming from the neutron star (second component, Comptb2) and the iron-line (Gaussian) component. Spectral analysis using this model indicates that the photon power-law indices Gamma_{com1} and Gamma_{com2} of the Comptonized components are almost constant, Gamma_{com1} and Gamma_{com2} ~ 2 when kT_e changes from 3 to 21 keV along Z-track. We interpret the detected quasi-stability of the indices of Comptonized components near a value of 2. Furthermore, this index stability now found for the Comptonized spectral components of Z-source GX 340+0 is similar to that was previously established in the atoll sources 4U~1728-34, GX 3+1 and early proposed for a number of X-ray neutron stars (NSs). This behavior of NSs both for atoll and Z-sources, is essentially different from that observed in black hole binaries where Gamma_{com} increases during a spectral evolution from the low state to the high state and ultimately saturates at high mass accretion rate.

30 pages, 5 Tables and 12 figures, the paper has been accepted and scheduled for publication in The Astrophysical Journal, for the March 20, 2013, v 766, 1st issue

References in corpus (6)

• RXTE observations of the first transient Z source XTE J1701-462: shedding new light on mass accretion in luminous neutron star LMXBs
• Effects of Downscattering on the Continuum and Line Spectra in Powerful Wind Environment. Monte Carlo Simulations, Analytical Results and Data Analysis
• Disk reflection signatures in the spectrum of the bright Z-source GX 340+0
• An explanation of the Z-track sources
• GX~3+1: the stability of spectral index as a function of mass accretion rate
• Correlations between X-ray Spectral and Timing Characteristics in Cyg X-2

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