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

Journal of astrophysics and astronomy

C. P. Huang¹  G. Q. Ding1¹ 

[1] Xinjiang Astronomical Observatory, CAS, 150 Science 1-Street, Urumqi 830011, China$$

关键词: Accretion: accretion disks—X-rays: binaries—stars: individual (GX 17+2)—stars: neutron.;   

DOI  :  

学科分类：天文学(综合)

来源: Indian Academy of Sciences

【 摘 要 】

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 X-ray 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.

【 授权许可】

Unknown