TY - JOUR
T1 - Results from the ASCA Large Sky Survey - Nature of faint X-ray sources and the implications for the origin of the CXB
AU - Ueda, Y.
AU - Akiyama, M.
AU - Hasinger, G.
AU - Inoue, H.
AU - Ishisaki, Y.
AU - Makishima, K.
AU - Ogasaka, Y.
AU - Ohta, K.
AU - Sakano, M.
AU - Takahashi, T.
AU - Tsuru, T.
AU - Voges, W.
AU - Yamada, T.
PY - 2000
Y1 - 2000
N2 - We report results from the ASCA Large Sky Survey (LSS), the first wide-area unbiased survey in the 0.7-10 keV band over a continuous region of 7 deg 2 near the north Galactic pole. Applying the newly developed source-detection method to the LSS data independently in the total (0.7-7 keV), hard (2-10 keV), and soft (0.7-2 keV) band, we detected 107 sources altogether with sensitivity limits of 6 × 10 -14 (0.7-7 keV), 1 × 10 -13 (2-10 keV), and 2 × 10 -14 erg s -1 cm -2 (0.7-2 keV), respectively. At these flux limits, 30(±3)% of the CXB in the 0.7-7 keV band and 23(±3)% in the 2-10 keV band have been resolved into discrete sources. The average spectrum of faint sources near the sensitivity limits show a photon index of 1.49±0.10 in the 2-10 keV range, and 1.63±0.07 in the 0.7-10 keV range. These spectral properties suggest that contribution of sources with hard energy spectra become significant at a flux level of 10 -13 erg s -1 cm -2 (2-10 keV). Optical identification for a sample of 34 sources detected in the hard band revealed that at least six of them are type-2 AGNs. We found a good correlation that hard sources correspond to type-2 AGNs, while the photon index of type-1 AGNs is distributed around 1.6-1.8 in the 0.7-10 keV range. Follow-up X-ray observations of selected five hard-sources indicate that their spectra are subject to heavy absorption with an intrinsic hydrogen column density of 10 22 ∼ 10 23 cm -2 . These results support the scenario that the CXB is the mixture of the emission from non-absorbed sources and absorbed sources.
AB - We report results from the ASCA Large Sky Survey (LSS), the first wide-area unbiased survey in the 0.7-10 keV band over a continuous region of 7 deg 2 near the north Galactic pole. Applying the newly developed source-detection method to the LSS data independently in the total (0.7-7 keV), hard (2-10 keV), and soft (0.7-2 keV) band, we detected 107 sources altogether with sensitivity limits of 6 × 10 -14 (0.7-7 keV), 1 × 10 -13 (2-10 keV), and 2 × 10 -14 erg s -1 cm -2 (0.7-2 keV), respectively. At these flux limits, 30(±3)% of the CXB in the 0.7-7 keV band and 23(±3)% in the 2-10 keV band have been resolved into discrete sources. The average spectrum of faint sources near the sensitivity limits show a photon index of 1.49±0.10 in the 2-10 keV range, and 1.63±0.07 in the 0.7-10 keV range. These spectral properties suggest that contribution of sources with hard energy spectra become significant at a flux level of 10 -13 erg s -1 cm -2 (2-10 keV). Optical identification for a sample of 34 sources detected in the hard band revealed that at least six of them are type-2 AGNs. We found a good correlation that hard sources correspond to type-2 AGNs, while the photon index of type-1 AGNs is distributed around 1.6-1.8 in the 0.7-10 keV range. Follow-up X-ray observations of selected five hard-sources indicate that their spectra are subject to heavy absorption with an intrinsic hydrogen column density of 10 22 ∼ 10 23 cm -2 . These results support the scenario that the CXB is the mixture of the emission from non-absorbed sources and absorbed sources.
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U2 - 10.1016/S0273-1177(99)00851-0
DO - 10.1016/S0273-1177(99)00851-0
M3 - Article
AN - SCOPUS:6744227968
SN - 0273-1177
VL - 25
SP - 839
EP - 844
JO - Advances in Space Research
JF - Advances in Space Research
IS - 3-4
ER -