31 research outputs found
On why the Iron K-shell absorption in AGN is not a signature of the local Warm/Hot Intergalactic Medium
We present a comparison between the 2001 XMM-Newton and 2005 Suzaku
observations of the quasar, PG1211+143 at z=0.0809. Variability is observed in
the 7 keV iron K-shell absorption line (at 7.6 keV in the quasar frame), which
is significantly weaker in 2005 than during the 2001 XMM-Newton observation.
From a recombination timescale of <4 years, this implies an absorber density
n>0.004 particles/cm3, while the absorber column is 5e22<N_H <1 1e24
particles/cm2. Thus the sizescale of the absorber is too compact (pc scale) and
the surface brightness of the dense gas too high (by 9-10 orders of magnitude)
to arise from local hot gas, such as the local bubble, group or Warm/Hot
Intergalactic Medium (WHIM), as suggested by McKernan et al. (2004, 2005).
Instead the iron K-shell absorption must be associated with an AGN outflow with
mildly relativistic velocities. Finally we show that the the association of the
absorption in PG1211+143 with local hot gas is simply a coincidence, the
comparison between the recession and iron K absorber outflow velocities in
other AGN does not reveal a one to one kinematic correlation.Comment: accepted for publication in MNRAS LETTERS. 5 pages, 4 figure
The Electron Scattering Region in Seyfert Nuclei
The electron scattering region (ESR) is one of important ingredients in
Seyfert nuclei because it makes possible to observe the hidden broad line
region (hereafter HBLR) in some type 2 Seyfert nuclei (hereafter S2s). However,
little is known about its physical and geometrical properties. Using the number
ratio of S2s with and without HBLR, we investigate statistically where the ESR
is in Seyfert nuclei. Our analysis suggests that the ESR is located at radius
between 0.01 pc and 0.1 pc from the central engine. We also
discuss a possible origin of the ESR briefly.Comment: 5 pages and 1 figure. The Astrophysical Journal (Letters), in pres
X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku
We report results from a Suzaku observation of the narrow-line Seyfert 1 NGC
4051. During our observation, large amplitude rapid variability is seen and the
averaged 2--10 keV flux is 8.1x10^-12 erg s^-1 cm^-2, which is several times
lower than the historical average. The X-ray spectrum hardens when the source
flux becomes lower, confirming the trend of spectral variability known for many
Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high and
low flux intervals are analyzed. The spectra are first fitted with a model
consisting of a power-law component, a reflection continuum originating in cold
matter, a blackbody component, two zones of ionized absorber, and several
Gaussian emission lines. The amount of reflection is rather large (R ~ 7, where
R=1 corresponds to reflection by an infinite slab), while the equivalent width
of the Fe-K line at 6.4 keV is modest (140 eV) for the averaged spectrum. We
then model the overall spectra by introducing partial covering for the
power-law component and reflection continuum independently. The column density
for the former is 1x10^23 cm^-2, while it is fixed at 1x10^24 cm-2 for the
latter. By comparing the spectra in different flux states, we identify the
causes of spectral variability. (abridged)Comment: 19 pages, 18 figures, accepted for publication in PASJ (Suzaku 3rd
special issue
Type I ULIRGs: Transition Stage from ULIRGs to QSOs
We examine whether the ultraluminous infrared galaxies that contain a type I
Seyfert nucleus (a type I ULIRG) are in the transition stage from ULIRGs to
quasi-stellar objects (QSOs). To inspect this issue, we compare the black hole
(BH) mass, the bulge luminosity and the far infrared luminosity among type I
ULIRGs, QSOs and elliptical galaxies. As a result, we find the following
results; (1) The type I ULIRGs have systematically smaller BH masses in spite
of the comparable bulge luminosity relative to QSOs and elliptical galaxies.
(2) The far-infrared luminosity of most type I ULIRGs is larger than the
Eddington luminosity. We show that above results do not change significantly
for 3 type I ULIRGs that we can estimate the visual extinction from the column
density. Also, for all 8 type I ULIRGs, we investigate the effect of
uncertainties of BH mass measurments and our sample bias, so that it turns out
that our results do not alter even if we consider above two effects. In
addition, Anabuki (2004) revealed that their X-ray properties are similar to
those of the narrow line Seyfert 1 galaxies. These would indicate that active
galactic nuclei (AGNs) with a high mass accretion rate exist in the type I
ULIRGs. Based on all of these findings, we conclude that it would be a natural
interpretation that type I ULIRGs are the early phase of BH growth, namely the
missing link between ULIRGs and QSOs. Moreover, by comparing our results with a
theoretical model of a coevolution scenario of a QSO BH and a galactic bulge,
we show clearly that this explanation would be valid.Comment: 11 pages, 4 figures, 4 tables accepted for publication in Ap
Monte-Carlo Simulator and Ancillary Response Generator of Suzaku XRT/XIS System for Spatially Extended Source Analysis
We have developed a framework for the Monte-Carlo simulation of the X-Ray
Telescopes (XRT) and the X-ray Imaging Spectrometers (XIS) onboard Suzaku,
mainly for the scientific analysis of spatially and spectroscopically complex
celestial sources. A photon-by-photon instrumental simulator is built on the
ANL platform, which has been successfully used in ASCA data analysis. The
simulator has a modular structure, in which the XRT simulation is based on a
ray-tracing library, while the XIS simulation utilizes a spectral
"Redistribution Matrix File" (RMF), generated separately by other tools.
Instrumental characteristics and calibration results, e.g., XRT geometry,
reflectivity, mutual alignments, thermal shield transmission, build-up of the
contamination on the XIS optical blocking filters (OBF), are incorporated as
completely as possible. Most of this information is available in the form of
the FITS (Flexible Image Transport System) files in the standard calibration
database (CALDB). This simulator can also be utilized to generate an "Ancillary
Response File" (ARF), which describes the XRT response and the amount of OBF
contamination. The ARF is dependent on the spatial distribution of the
celestial target and the photon accumulation region on the detector, as well as
observing conditions such as the observation date and satellite attitude. We
describe principles of the simulator and the ARF generator, and demonstrate
their performance in comparison with in-flight data.Comment: 19 pages with 8 figures, accepted for publication in PASJ Vol 58,
Suzaku special issu
Hitomi (ASTRO-H) X-ray Astronomy Satellite
The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month
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The quiescent intracluster medium in the core of the Perseus cluster
Clusters of galaxies are the most massive gravitationally bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and many astrophysical processes. However, knowledge of the dynamics of the pervasive hot gas, the mass of which is much larger than the combined mass of all the stars in the cluster, is lacking. Such knowledge would enable insights into the injection of mechanical energy by the central supermassive black hole and the use of hydrostatic equilibrium for determining cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50-million-kelvin diffuse hot plasma filling its gravitational potential well. The active galactic nucleus of the central galaxy NGC 1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These bubbles probably induce motions in the intracluster medium and heat the inner gas, preventing runaway radiative cooling - a process known as active galactic nucleus feedback. Here we report X-ray observations of the core of the Perseus cluster, which reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of 164 ± 10 kilometres per second in the region 30-60 kiloparsecs from the central nucleus. A gradient in the line-of-sight velocity of 150 ± 70 kilometres per second is found across the 60-kiloparsec image of the cluster core. Turbulent pressure support in the gas is four per cent of the thermodynamic pressure, with large-scale shear at most doubling this estimate. We infer that a total cluster mass determined from hydrostatic equilibrium in a central region would require little correction for turbulent pressure.Please visit the publisher's website for funding information