X-ray Spectroscopy of Galactic Hot Gas along the PKS 2155-304 Sight Line

We present a detailed spectroscopic study of the hot gas in the Galactic halo toward the direction of a blazer PKS 2155-304 (z=0.117). The OVII and OVIII absorption lines are measured with the Low and High Energy Transmission Grating Spectrographs aboard Chandra, and the OVII, OVIII, and NeIX emission lines produced in the adjacent field of the PKS 2155-304 direction are observed with the X-ray Imaging Spectrometer aboard Suzaku. Assuming vertically exponential distributions of the gas temperature and the density, we perform a combined analysis of the absorption and emission data. The gas temperature and density at the Galactic plane are determined to be 2.5(+0.6,-0.3) MK and 1.4(+0.5,-0.4) x 10^{-3} cm^{-3} and the scale heights of the gas temperature and density are 5.6(+7.4,-4.2) kpc and 2.3(+0.9,-0.8) kpc, respectively. These values are consistent with those obtained in the LMC X-3 direction.

💡 Research Summary

This paper presents a detailed spectroscopic study of the hot gas in the Galactic halo towards the direction of the blazar PKS 2155-304 (z=0.117). The OVII and OVIII absorption lines were measured using the Low and High Energy Transmission Grating Spectrographs aboard Chandra, while the OVII, OVIII, and NeIX emission lines produced in the adjacent field of PKS 2155-304 were observed with Suzaku’s X-ray Imaging Spectrometer. Assuming vertically exponential distributions for gas temperature and density, a combined analysis of absorption and emission data was performed. The study determined that the gas temperature at the Galactic plane is approximately 2.5(+0.6,-0.3) MK, and its density is about 1.4(+0.5,-0.4) x 10^{-3} cm^{-3}. Additionally, the scale heights for gas temperature and density were found to be 5.6(+7.4,-4.2) kpc and 2.3(+0.9,-0.8) kpc respectively. These findings are consistent with those obtained in the LMC X-3 direction, providing further insights into the physical characteristics of the Galactic halo.