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Evolution of Hard X-Ray Spectra Along the Branches in Cir X-1

G. Q. Ding·J. L. Qu·T. P. Li
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Abstract

Using the data from the PCA and HEXTE on board the RXTE satellite, we investigate the evolution of the 3-200 keV spectra of the peculiar low mass X-ray binary (LMXB) Cir X-1 along the branches on its hardness-intensity diagram (HID) from the vertical horizontal branch (VHB), through the horizontal horizontal branch (HHB) and normal branch (NB), to the flaring branch (FB). We detect a power-law hard component in the spectra. It is found that the derived photon indices ($Γ$) of the power-law hard component are correlated with the position on the HID. The power-law component dominates the X-ray emission of Cir X-1 in the energy band higher than $\sim 20$ keV. The fluxes of the power-law component are compared with those of the bremsstrahlung component in the spectra. A possible origin of the power-law hard component is discussed.

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G. Q. Ding, J. L. Qu, T. P. Li. 2003-09-05. Evolution of Hard X-Ray Spectra Along the Branches in Cir X-1. https://doi.org/10.1086/379338

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