38 research outputs found
Reflection Component in the Hard X-Ray Emission from the Seyfert 2 Galaxy Mrk 1210
The Seyfert 2 galaxy Mrk 1210 was found to exhibit a flat hard X-ray
component by ASCA, although ASCA could not distinguish whether it is an
absorbed direct component or a reflected one. We then observed Mrk 1210 with
BeppoSAX, and found that the X-ray spectral properties are quite different from
those of ASCA, as have been confirmed with XMM-Newton; the flux is
significantly higher than that in the ASCA observation, and a clear absorption
cut-off appears below 5 keV. A bright hard X-ray emission is detected up to 100
keV. The reflection component is necessary to describe the BeppoSAX PDS
spectrum, and represents the ASCA hard component very well. Therefore, the hard
component in the ASCA spectrum is a reflected one, whose intensity is almost
constant over 6 years. This indicates that a dramatic spectral variability is
attributed to a large change of the absorption column density by a factor of
>5, rather than the variability of the nuclear emission. The change in the
absorption-column density means that the torus is not homogeneous, but has a
blobby structure with a typical blob size of < 0.001Comment: 9 pages, 5 figures, accepted for Pablications for the Astronomical
Society of Japa
Long-term X-ray variability of quasars in the Lockman Hole field observed with ROSAT
An improved method is utilized to estimate the X-ray power spectral densities
(PSD) and the variation time scales of three quasars in the Lockman Hole field.
Five archival ROSAT PSPC data covering two year range are analyzed. To estimate
PSD from sparse and unevenly-sampled lightcurves, a forward-method approach
with extensive Monte-Carlo simulations is adopted. A broken power-law type PSD
with a constant Poisson noise component is assumed with a break frequency
. Then, assuming the PSD slope as , is constrained as 25 days for one object, while the
constraints on the other two objects are very weak. The long time scale of the
one object is consistent with the view that luminous AGNs host massive black
holes.Comment: 8 pages, 3 figures, accepted in PAS
The Declined Activity in the Nucleus of NGC 1316
NGC 1316 (Fornax A) is a radio galaxy with prototypical double lobes, where
the magnetic field intensity is accurately measured via the inverse-Compton
technique. The radio-emitting electrons in the lobes are inferred to have a
synchrotron life time of 0.1 Gyr. Considering the lobe energetics, we estimate
the past nuclear X-ray luminosity of NGC 1316 to be at least 4 times 10^{34} W
(4 times 10^{41} erg s^{-1}). Thus, the nucleus was rather active at least 0.1
Gyr ago. In contrast, we confirmed with ASCA and ROSAT that the nucleus of NGC
1316 is very faint in X-rays at present, with the 2--10 keV luminosity of any
AGN-like hard component being < 2 times 10^{33} W (2 times 10^{40} erg s^{-1})
even assuming a nuclear obscuration up to 10^{28} m^{-2} (10^{24} cm^{-2}).
This is at least an order of magnitude lower than the estimated past activity,
indicating that the nucleus is presently very inactive. From these two results,
we conclude that the nucleus of NGC 1316 has become dormant during the last 0.1
Gyr. This suggests the possible abundance of ``dormant'' quasars in nearby
galaxies.Comment: 7 pages, 2 figures, to be published in the Astrophysical Journal
Letter
Absorber Materials for Transition-Edge Sensor X-ray Microcalorimeters
Arrays of superconducting transition-edge sensors (TES) can provide high spatial and energy resolution necessary for x-ray astronomy. High quantum efficiency and uniformity of response can be achieved with a suitable absorber material, in which absorber x-ray stopping power, heat capacity, and thermal conductivity are relevant parameters. Here we compare these parameters for bismuth and gold. We have fabricated electroplated gold, electroplated gold/electroplated bismuth, and evaporated gold/evaporated bismuth 8x8 absorber arrays and find that a correlation exists between the residual resistance ratio (RRR) and thin film microstructure. This finding indicates that we can tailor absorber material conductivity via microstructure alteration, so as to permit absorber thermalization on timescales suitable for high energy resolution x-ray microcalorimetry. We show that by incorporating absorbers possessing large grain size, including electroplated gold and electroplated gold/electroplated bismuth, into our current Mo/Au TES, devices with tunable heat capacity and energy resolution of 2.3 eV (gold) and 2.1 eV (gold/bismuth) FWHM at 6 keV have been fabricated
The ASTRO-H X-ray Observatory
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly
successful X-ray missions initiated by the Institute of Space and Astronautical
Science (ISAS). ASTRO-H will investigate the physics of the high-energy
universe via a suite of four instruments, covering a very wide energy range,
from 0.3 keV to 600 keV. These instruments include a high-resolution,
high-throughput spectrometer sensitive over 0.3-2 keV with high spectral
resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in
the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers
covering 5-80 keV, located in the focal plane of multilayer-coated, focusing
hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12
keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and
a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the
40-600 keV band. The simultaneous broad bandpass, coupled with high spectral
resolution, will enable the pursuit of a wide variety of important science
themes.Comment: 22 pages, 17 figures, Proceedings of the SPIE Astronomical
Instrumentation "Space Telescopes and Instrumentation 2012: Ultraviolet to
Gamma Ray
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 a host of astrophysical processes. Knowledge of the
dynamics of the pervasive hot gas, which dominates in mass over stars in a
cluster, is a crucial missing ingredient. It can enable new insights into
mechanical energy injection by the central supermassive black hole and the use
of hydrostatic equilibrium for the determination of cluster masses. X-rays from
the core of the Perseus cluster are emitted by the 50 million K diffuse hot
plasma filling its gravitational potential well. The Active Galactic Nucleus of
the central galaxy NGC1275 is pumping jetted energy into the surrounding
intracluster medium, creating buoyant bubbles filled with relativistic plasma.
These likely 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 on Hitomi X-ray observations of the Perseus
cluster core, which reveal a remarkably quiescent atmosphere where the gas has
a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from
the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s
is found across the 60 kpc image of the cluster core. Turbulent pressure
support in the gas is 4% or less of the thermodynamic pressure, with large
scale shear at most doubling that estimate. We infer that total cluster masses
determined from hydrostatic equilibrium in the central regions need little
correction for turbulent pressure.Comment: 31 pages, 11 Figs, published in Nature July