STABILITY OF THE PHOTON INDICES IN Z-SOURCE GX 340+0 FOR SPECTRAL STATES
- Moscow State University/Sternberg Astronomical Institute, Universitetsky Prospect 13, Moscow 119992 (Russian Federation)
- Dipartimento di Fisica, Universita di Ferrara, Via Saragat 1, I-44122 Ferrara (Italy)
We show an analysis of the spectral and timing properties of X-ray radiation from Z-source GX 340+0 during its evolution when the electron temperature of the transition layer (TL) kT{sub e} monotonically decreases from 21 to 3 keV. We analyze episodes observed with BeppoSAX and RXTE. We reveal that the X-ray broadband energy spectra during all spectral states can be reproduced by a physical model composed of a soft Blackbody component and two Comptonized components (both due to the presence of the TL that upscatters both seed photons of T{sub s1} {approx}< 1 keV coming from the disk (first component Comptb1), and seed photons of temperature T{sub s2} {approx}< 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}{sub com1} and {Gamma}{sub com2} of the Comptonized components are almost constant, {Gamma}{sub com1} and {Gamma}{sub com2} {approx} 2 when kT{sub e} changes from 3 to 21 keV along the Z-track. We interpret the detected quasi-stability of the indices of Comptonized components to be 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 previously established in the atoll sources 4U 1728-34 and GX 3+1, and earlier 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}{sub com} increases during a spectral evolution from the low state to the high state and ultimately saturates at a high mass accretion rate.
- OSTI ID:
- 22167543
- Journal Information:
- Astrophysical Journal, Vol. 766, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
BeppoSax and RXTE spectral study of the low-mass X-ray binary 4U 1705–44: Spectral hardening during the banana branch
SPECTRAL STATE EVOLUTION OF 4U 1820-30: THE STABILITY OF THE SPECTRAL INDEX OF THE COMPTONIZATION TAIL