Log N - Log S Relations and Spectral Properties of Sources from the ASCA Large Sky Survey --- their Implications for the Origin of the Cosmic X-ray Background (CXB)

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dc.creatorUeda, Y.
dc.creatorTakahashi, T.
dc.creatorInoue, H.
dc.creatorTsuru, T.
dc.creatorSakano, M.
dc.creatorIshisaki, Y.
dc.creatorOgasaka, Y.
dc.creatorMakishima, K.
dc.creatorYamada, T.
dc.creatorAkiyama, M.
dc.creatorOhta, K.
dc.date1999-01-09
dc.date1999-03-24
dc.date.accessioned2026-07-07T10:51:23Z
dc.date.available2026-07-07T10:51:23Z
dc.descriptionWe carried out the first wide-area unbiased survey with the ASCA satellite in the 0.7-10 keV band around a north Galactic-pole region covering a continuous area of 7 square degrees (Large Sky Survey; LSS). To make the best use of ASCA capability, we developed a new source-detection method where the complicated detector responses are fully taken into account. Applying this method to the entire 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 x 10E-14 (0.7-7 keV), 1 x 10E-13 (2-10 keV), and 2 x 10E-14 erg sE-1 cmE-2 (0.7-2 keV), respectively. A complete list of the detected sources is presented. Based on detailed studies by Monte Carlo simulations, we evaluated effects of the source confusion and accurately derived Log N - Log S relation in each survey band. The Log N - Log S relation in the hard band is located on the extrapolation from the GINGA and HEAO1 results with the Euclidean slope of -3/2, while that in the soft band is consistent with the results by ROSAT. At these flux limits, 30 (+/- 3) percent of the CXB in the 0.7-7 keV band and 23 (+/- 3) percent in the 2-10 keV band have been resolved into discrete sources. The average spectrum of faint sources detected in the total band shows a photon index of 1.63 +/- 0.07 in the 0.7-10 keV range, consistent with the comparison of source counts between the hard and the soft energy band. Those detected in the hard band show a photon index of 1.49 +/- 0.10 in the 2-10 keV range. These spectral properties suggest that contribution of sources with hard energy spectra become significant at a flux of 10E-13 erg sE-1 cmE-2 (2-10 keV). The most plausible candidates are type-II AGNs, as indicated by on-going optical identifications.
dc.description28 pages, 11 figures, to appear in ApJ 518, 1999; figure 1 replaced, minor errors in text corrected
dc.identifierhttps://arxiv.org/abs/astro-ph/9901101
dc.identifierhttp://arxiv.org/abs/astro-ph/9901101
dc.identifierAstrophys.J.518:656,1999
dc.identifierdoi:10.1086/307291
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/184804
dc.subjectAstrophysics
dc.titleLog N - Log S Relations and Spectral Properties of Sources from the ASCA Large Sky Survey --- their Implications for the Origin of the Cosmic X-ray Background (CXB)
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