53 research outputs found
X-ray and Sunyaev-Zeldovich properties of the WHIM
We use numerical simulations to predict the soft X-ray ([0.4-0.6] keV) and
Sunyaev-Zeldovich signal (at 150 GHz) from the large scale structure in the
Universe and then compute 2-point statistics to study the spatial distribution
and time evolution of the signals. The average X-ray signal predicted for the
WHIM is in good agreement with observational constraints that set it at about
10% of the total Diffuse X-ray Background. The characteristic angle computed
with the Autocorrelation Function is of the order of some arcminutes and
becomes smaller at higher redshift. The power spectrum peak of the SZ due to
the WHIM is at l~10000 and has amplitude of ~0.2 muK^2, about one order of
magnitude below the signal measured with telescopes like Planck, ACT, and SPT.
Even if the high-redshift WHIM signal is too weak to be detected using X-rays
only, the small-scale correlation between X-ray and SZ maps is dominated by the
high-redshift WHIM. This makes the analysis of the SZ signal in support of
X-rays a promising tool to study the early time WHIM.Comment: 13 Pages, 10 Figures, Accepted for Publication on Ap
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
Seismological constraints for the dyke emplacement of the July-August 2001 lateral eruption at Mt. Etna volcano, Italy
In this paper we report seismological evidence regarding the emplacement of the dike that fed the July 18 - August 9, 2001 lateral eruption at Mt. Etna volcano. The shallow intrusion and the opening of the eruptive fracture system, which mostly occurred during July 12, and July 18, were accompanied by one of the most intense seismic swarms of the last 20 years. A total of 2694 earthquakes (1 £ Md £ 3.9) were recorded from the beginning of the swarm (July 12) to the end of the eruption (August 9). Seismicity shows the upward migration of the dike from the basement to the relatively thin volcanic pile. A clear hypocentral migration was observed, well constraining the upwards propagation of a near-vertical dike, oriented roughly N-S, and located a few kilometers south of the summit region. Earthquake distribution and orientation of the P-axes from focal mechanisms indicate that the swarm was caused by the local stress source related to the dike intrusion
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
Hitomi X-Ray Studies of Giant Radio Pulses from the Crab Pulsar
To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2300 keV band and the Kashima NICT radio telescope in the 1.41.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 fluctuations of the X-ray fluxes at the pulse peaks, and the 3 upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.510 keV and 70300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) 10(exp 11) erg cm(exp 2), respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a >0.02% brightening of the pulse-peak flux under such conditions
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The X-ray flux from the warm-hot intergalactic medium
In the past years significant efforts have been focused on describing the evolution and structure of the Universe. One of the big open questions in cosmology is Where is the baryonic mass ? We know from various surveys that the number of detected baryons in the Universe at present days is much smaller than predicted by the standard big-bang nucleosynthesis model and measured by the detailed observation of the Lyman-alpha forest at redshift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a warm-hot (10 5-107 K) filamentary gas, distributed in the intergalactic medium. This gas, if exists, should be highly ionized and observable only in the soft x-ray and UV bands. The first part of my project is dedicated to studying the evolution of the baryonic mass in the intergalactic medium using the output of hydrodynamic simulations. In the second part I use the same simulations to predict the x-ray flux from the Warm-Hot Intergalactic Medium (WHIM), its distribution in space and its spectral properties. The primary motivation of this investigation is the construction and launch of a dedicated mission to detect and study the properties of the intergalactic medium and the missing baryons. What I found is that, depending on the model, in the 0.37-0.925 keV energy band the WHIM is between 3% and 20% of the Diffuse X-Ray Background, and comes mostly from filaments between redshift 0.1 and 0.8. The filaments have typical angular size of a few arc minutes, which requires an detector angular resolution of 2\u27 or less. Since the identification of the WHIM is possible only from emission lines, we need a detector with energy resolution in the order of 4 eV or less. Another critical issue is the detector background which needs to be less than 10-3 counts s -1 eV-1 in order to detect the weak signal from the WHIM
Effect of the Metallicity on the X-ray Emission from the Warm-Hot Intergalactic Medium
Astrophys.J.721:46-58,2010 Hydrodynamic simulations predict that a significant fraction of the gas in
the current Universe is in the form of high temperature, highly ionized plasma
emitting and absorbing primarily in the soft X-ray and UV bands, dubbed the
Warm-Hot Intergalactic Medium (WHIM). Its signature should be observable in
red-shifted emission and absorption lines from highly ionized elements. To
determine the expected WHIM emission in the soft X-ray band we used the output
of a large scale hydrodynamic SPH simulation to generate images and spectra
with angular resolution of 14'' and energy resolution of 1 eV. The current
biggest limit of any hydrodynamic simulation in predicting the X-ray emission
comes from metal diffusion. In our investigation, by using four different
models for the WHIM metallicity we have found a strong dependence of the
emission on the model used, with differences up to almost an order of
magnitude. For each model we have investigated the redshift distribution and
angular scale of the emission, confirming that most photons come from redshift
z<1.2 and that the emission has a typical angular scale of less than a few
arcminutes. We also compared our simulations with the few currently available
observations and found that, within the variation of the metallicity models,
our predictions are in good agreement with current constraints on the WHIM
emission, and at this time the weak experimental constraints on the WHIM
emission are not sufficient to exclude any of the models used
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