%0 Journal Article
%T Chandra Observations of Two High-Redshift Quasars
%A T. Fang
%A H. L. Marshall
%A G. L. Bryan
%A C. R. Canizares
%J Physics
%D 2001
%I arXiv
%R 10.1086/321473
%X We report the first high-resolution X-ray spectra of two high-redshift quasars, S5 0836+710 and PKS 2149-306, obtained with the Chandra High Energy Transmission Grating Spectrometer (HETGS). The primary goal of this observation is to use the high spectral resolving power of the HETGS to detect X-ray absorption produced by a hot intergalactic medium. The continuum of both quasars can be fitted by absorbed power laws. The power law photon index (Gamma) of S5 0836+710 is consistent with that found in previous observations with ROSAT and ASCA, while the power law of PKS 2149-306 is harder than found in a previous observation by ASCA. Excess continuum absorption above the Galactic value is found in S5 0836+710, as evidenced in ASCA and ROSAT observations. No significant emission or absorption feature is detected in either source at 3 sigma level. Based on the detection limits we constrain the properties of possible emitters and absorbers. The upper limit of the equivalent width of Fe K emission lines could be as low as ~ 10 eV. Absorbers with a column density higher than 8e16 cm^{-2} for O VIII or 5e16 cm^{-2} for Si XIV would have been detected. We propose a method to constrain the cosmological parameters (namely Omega_0 and Omega_b) via the X-ray forest theory, but current data do not give significant constraints. However, we estimate that observing ~ 7 bright quasars should give at least one O VIII and more O VII absorption lines at 95% possibility. We also find that combined with the constraints from the distortion of the CMB spectrum, the X-ray Gunn-Peterson test can marginally constrain a uniform, enriched IGM.
%U http://arxiv.org/abs/astro-ph/0102370v1