818 research outputs found
Spectral Statistics and Local Luminosity Function of a Hard X-ray Complete Sample of Brightest AGNs
We have measured the X-ray spectral properties of a complete flux-limited
sample of bright AGNs from HEAO-1 all-sky catalogs to investigate their
statistics and provide greater constraints on the bright-end of the hard X-ray
luminosity function (HXLF) of AGNs and the AGN population synthesis model of
the X-ray background. Spectral studies using data from ASCA, XMM-Newton and/or
Beppo-SAX observations have been made for almost all AGNs in this sample.
The spectral measurements enable us to construct the neutral absorbing column
density (Log nH) distribution and separate HXLFs for absorbed (Log nH[cm-2]>
21.5) and unabsorbed AGNs in the local universe. Our results show evidence for
a difference in the shapes of HXLFs of absorbed and unabsorbed AGNs in that
absorbed AGN HXLF drops more rapidly at higher luminosities than that of
unabsorbed AGNs, which is similar to that previously reported. In the Lx - nH
plot, we found no AGN in the high-luminosity high-intrinsic absorption regime
(Log Lx[erg/s]> 44.5, Log nH[cm-2]> 21.5) in our sample, where we expect about
5 AGNs if we assume that absorbed and unabsorbed having identical AGN HXLF
shapes. We also find that the observed flux with ASCA or XMM-Newton is smaller
than that with HEAO-1 by a factor of 0.29 on average, which is expected for
re-observation of sources with a factor 2.5 variability amplitude scale.Comment: 43 pages(one column), 10 figures(5 electronic only figures have been
included in the preprint source (tar.gz file)), accepted by The Astronomical
Journal, 9. Mar 200
Spectral Statistics and Luminosity Function of a Hard X-ray Complete Sample of Brightest AGNs
We investigated the statistics of the X-ray spectral properties of a complete
flux-limited sample of bright AGNs from HEAO-1 all-sky catalogs to provide the
bright end constraint of the evolution of AGN hard X-ray luminosity function
(HXLF) and the AGN population synthesis model of the X-ray background. Spectral
studies have been made using ASCA and XMM-Newton observation data for almost
all AGNs in this sample.Comment: PTPTex v0.88, 2 pages with 4 figures, Proceedings of the
"Stellar-Mass, Intermediate -Masss, and Supermassive Black Holes" in Kyoto,
Japa
Multiple Components of the Luminous Compact X-ray Source at the Edge of Holmberg II observed by ASCA and ROSAT
We report the results of the analysis of ASCA/ROSAT observations of the
compact luminous X-ray source found at the edge of the nearby star-forming
dwarf galaxy Holmberg II (UGC 4305).Our ASCA spectrum revealed that the X-ray
emission extends to the hard band and can be best described by a power-law with
a photon spectral index of 1.9. The ASCA spectrum does not fit with a
multi-color disk blackbody. The joint ASCA-ROSAT spectrum suggests two
components to the spectrum: the hard power-law component and a warm thermal
plasma kT~0.3[keV]. An additional absorption over that of our galaxy is
required. The wobble correction of the ROSAT HRI image has clearly unveiled the
existence of an extended component which amounts to 27+/-5% of the total X-ray
emission.
These observations indicate that there are more than one component in the
X-ray emission. The properties of the point-like component is indicative of an
accretion onto an intermediate mass blackhole, unless a beaming is taking
place. We argue that the extended component does not come from electron
scattering and/or reflection by scattered optically-thick clouds of the central
radiation. Possible explanations of this X-ray source include multiple
supernova remnants feeding an intermediate-mass blackhole. (abridged)Comment: 12 pages, 6 figures accepted to Astronomical Journa
Coevolution of Supermassive Black Holes and Circumnuclear Disks
We propose a new evolutionary model of a supermassive black hole (SMBH) and a
circumnuclear disk (CND), taking into account the mass-supply from a host
galaxy and the physical states of CND. In the model, two distinct accretion
modes depending on gravitational stability of the CND play a key role on
accreting gas to a SMBH. (i) If the CMD is gravitationally unstable, energy
feedback from supernovae (SNe) supports a geometrically thick, turbulent gas
disk. The accretion in this mode is dominated by turbulent viscosity, and it is
significantly larger than that in the mode (ii), i.e., the CMD is supported by
gas pressure. Once the gas supply from the host is stopped, the high accretion
phase () changes to the low one (mode
(ii), ), but there is a delay with yr. Through this evolution, the gas-rich CND turns into the gas poor
stellar disk. We found that not all the gas supplied from the host galaxy
accrete onto the SMBH even in the high accretion phase (mode (i)), because the
part of gas is used to form stars. As a result, the final SMBH mass () is not proportional to the total gas mass supplied from the host
galaxy (); decreases with .This would indicate that it is difficult to form a SMBH with observed at high- QSOs. The evolution of the SMBH and CND would
be related to the evolutionary tracks of different type of AGNs.Comment: 11 pages, 11 figures, accepted for publication in Ap
Chandra survey in the AKARI North Ecliptic Pole Deep Field. I. X-ray data, point-like source catalog, sensitivity maps, and number counts
We present data products from the 300 ks Chandra survey in the AKARI North
Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared
photometry covering 2-24 micron from the AKARI Infrared Camera, including
mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the
deepest ever achieved at ~15 micron, and is by far the widest among those with
similar depths in the MIR. This makes this field unique for the MIR-selection
of AGN at z~1. We design a source detection procedure, which performs joint
Maximum Likelihood PSF fits on all of our 15 mosaicked Chandra pointings
covering an area of 0.34 square degree. The procedure has been highly optimized
and tested by simulations. We provide a point source catalog with photometry
and Bayesian-based 90 per cent confidence upper limits in the 0.5-7, 0.5-2,
2-7, 2-4, and 4-7 keV bands. The catalog contains 457 X-ray sources and the
spurious fraction is estimated to be ~1.7 per cent. Sensitivity and 90 per cent
confidence upper flux limits maps in all bands are provided as well. We search
for optical MIR counterparts in the central 0.25 square degree, where deep
Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected
there, ~80 per cent have optical counterparts and ~60 per cent also have AKARI
mid-IR counterparts. We cross-match our X-ray sources with MIR-selected AGN
from Hanami et al. (2012). Around 30 per cent of all AGN that have MID-IR SEDs
purely explainable by AGN activity are strong Compton-thick AGN candidates.Comment: 23 pages, 20 figures; catalogs, sensitivity maps, and upper limit
flux maps are available from the VizieR Servic
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