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Title:
Observations of the high-redshift quasar Q1745+624 (z=3.9) with ASCA
Authors:
Kubo, H.; Makishima, K.; Takahashi, T.; Ishida, M.; Inoue, H.; Matsuoka, M.; Yamasaki, N.; Suzuki, K.
Affiliation:
AA(Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan ), AB(Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan ), AC(Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229, Japan ), AD(Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229, Japan ), AE(Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229, Japan ), AF(The Institute of Physical and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-01, Japan ), AG(Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji 192-03, Japan ), AH(Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan )
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 287, Issue 2, pp. 328-332. (MNRAS Homepage)
Publication Date:
05/1997
Origin:
MNRAS
MNRAS Keywords:
QUASARS: INDIVIDUAL: Q1745+624, X-RAYS: GALAXIES
Bibliographic Code:
1997MNRAS.287..328K

Abstract

Q1745+624 is located at redshift z=3.89, and is one of the most distant quasars observed in the X-ray band. Q1745+624 was clearly detected with ASCA in the 0.5-7keV X-ray band, or in 2.4-34keV in the quasar rest frame. If the energy spectrum is fitted by a single power law with photoelectric absorption, the photon index becomes 1.68^+0.25_-0.24, and the column density N_H becomes 2.1^+1.5_-1.4x10^21cm^-2, assuming the absorber to be located at z=0. This index is steeper than that of the cosmic X-ray background. The spectrum suggests the presence of excess absorption above the Galactic column. If the absorber is at the same redshift as the quasar, then the intrinsic column density N_H is inferred to be 6.1^+10.8_-5.9x10^22cm^-2, which is comparable to that seen in nearby Seyfert 2 galaxies. The spectrum shows neither flattening above ~10keV in the rest frame nor a significant Fe K line. This is in contrast to the X-ray properties of nearby Seyfert galaxies. When compared to lower redshift radio-loud quasars, Q1745+624 is inferred to have ~10 times higher luminosity, but a very similar X-ray spectral index as well as a similar spectral energy distribution from the radio to the X-ray bands.

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