The X-Ray Telescope onboard Suzaku Serlemitsos, Peter J; Soong, Yang; Chan, Kai-Wing ...
Publications of the Astronomical Society of Japan,
01/2007, Letnik:
59, Številka:
sp1
Journal Article
Recenzirano
Odprti dostop
We present the design parameters, production process, and in-flight performance of the X-ray telescope (XRT) onboard Suzaku. The imaging capability is significantly improved over the ASCA XRT, which ...had half-power diameters of
${3\rlap {.}{}^{\mathrm {\prime }}6}$
, to
${1\rlap {.}{}^{\mathrm {\prime }}8}$
–
${2\rlap {.}{}^{\mathrm {\prime }}3}$
for all four XRT-I modules. The optical axes are found to be distributed within a radius of
${1\rlap {.}{}^{\mathrm {\prime }}3}$
, which makes the observation efficiency of all the XRTs more than 97% at the XIS-default observing position. The vignetting over the XIS field of view predicted via ray-tracing coincides with that measured for observations of the Crab Nebula to within
$\sim 10\%$
. Contemporaneous fits of a power law to all of the XIS spectra of the Crab Nebula taken at the two standard observing positions (XIS/HXD-default positions) gives a flux consistent with that obtained by Toor and Seward (1974, AJ, 79, 995) to within
$\sim 2\%$
. The pre-collimator on the top of each XRT module successfully reduces the intensity of the stray light from the
$20'$
and
$50'$
-off directions down to the level of pre-flight expectations.
Abstract
We present the Chandra and Suzaku observations of 1RXS J170047.8−314442, located towards the Galactic bulge, to reveal a wide-band (0.3–10 keV) X-ray morphology and spectrum of this source. ...With the Chandra observation, no point source was found at the position of 1RXS J170047.8−314442. Instead, we revealed the presence of diffuse X-ray emission, via the wide-band X-ray image obtained from the Suzaku XIS. Although the X-ray emission had a nearly circular shape with a spatial extent of ∼3
${^{\prime}_{.}}$
5, the surface brightness profile was not axisymmetric; a bright spot-like emission was found at ∼ 1΄ away in the northwestern direction from the center. The radial profile of the surface brightness, except for this spot-like emission, was reproduced with a single β-model; β and the core radius were found to be 1.02 and 1
${^{\prime}_{.}}$
51, respectively. The X-ray spectrum of the diffuse emission showed an emission line at ∼6 keV, indicating an origin of a thermal plasma. The spectrum was well explained with an absorbed, optically-thin thermal plasma model with a temperature of 6.2 keV and a redshift parameter of z = 0.14 ± 0.01. Hence, the X-ray emission was considered to arise from the hot gas associated with a cluster of galaxies. Our spectroscopic result confirmed the optical identification of 1RXS J170047.8−314442 by Kocevski et al. (2007, ApJ, 662, 224): CIZA J1700.8−3144, a member of the cluster catalogue in the Zone of Avoidance. The estimated bolometric X-ray luminosity of 5.9 × 1044 erg s−1 was among the lowest with this temperature, suggesting that this cluster is far from relaxed.
Supernova remnants (
$=$
SNR) are suggested to be sites of cosmic-ray acceleration. In particular, it has been an issue of keen interest whether cosmic ray protons are being accelerated in a SNR ...which emits TeV
$\gamma$
-rays. A crucial observational test for this is to find dense molecular gas towards the SNR, because such molecular gas can best verify the existence of cosmic-ray protons via pion decay to
$\gamma$
-rays. Here, we show that new high-resolution mm-wave observations of interstellar CO molecule have revealed molecular gas at 1 kpc distance interacting with the TeV
$\gamma$
-ray SNR G 347.3
$-$
0.5, and that a molecular cloud of
$\sim 200$
solar masses is clearly associated with the TeV
$\gamma$
-ray peak, providing strong evidence for proton acceleration. We have estimated the total energy of accelerated protons to be
$\sim 1048 \,\mathrm{erg}$
, which corresponds to an acceleration efficiency of
$\sim 0.001$
, posing an observational constraint on the proton acceleration.
Most of the cosmic baryons predicted by the big-bang nucleosynthesis have evaded direct detection. Recent numerical simulations indicate that approximately 30 to 50 percent of the total baryons in ...the present universe are supposed to take the form of warm/hot intergalactic medium (WHIM) whose X-ray continuum emission is very weak. To identify those missing baryons, we consider in detail the detectability of WHIM directly through the emission lines of O VII (561, 568, 574, 665 eV) and O VIII (653 eV). For this purpose, we create mock spectra of the emission lines of WHIM using a light-cone output of cosmological hydrodynamic simulations. While the predicted fluxes are generally below the current detection limit, an unambiguous detection will be feasible with a dedicated X-ray satellite mission, which we also discuss in detail. Our proposed mission is especially sensitive to a WHIM with gas temperature of
$T = 10^{6 \hbox{--} 7} \,\mathrm{K}$
and overdensity of
$\delta = 10 \hbox{--} 100$
up to a redshift of 0.3 without being significantly contaminated by the cosmic X-ray background and the Galactic emissions. Thus, such a mission provides a unique and important tool to identify a large fraction of otherwise elusive baryons in the universe.
The metal abundances in the interstellar medium of the isolated elliptical galaxy NGC 720 were studied with the CCD X-ray Imaging Spectrometer (XIS) aboard the Suzaku satellite. The high detection ...efficiency along with the excellent spectral resolution of the XIS allowed the K-shell lines of O and Mg to be clearly resolved, and the abundances of O, Ne, Mg, Si, and Fe to be measured with good accuracy for the region within a 3
$'$
radius of NGC 720. The abundances of O and Mg were well determined to be 0.4 and 0.5 solar respectively, meaning stellar metallicity of mass-losing stars in NGC 720 was also well determined. The abundance of Fe was determined to be about 0.7 solar, while the O
$/$
Fe, Ne
$/$
Fe abundance ratios were found to be about 0.5 and Mg
$/$
Fe, Si
$/$
Fe were found to be 0.7 in solar units. Relative errors of 30% for the O
$/$
Fe, Ne
$/$
Fe, Mg
$/$
Fe abundance ratios are the lowest among isolated elliptical galaxies so far observed. The higher abundance of Fe than those of O, Ne, and Mg supplied by stellar mass loss indicates that iron is enhanced by SN Ia in NGC 720. These abundance ratios are consistent with those in the ISM of NGC 1399, NGC 1404, and in the ICM of the Fornax cluster observed with Suzaku.
Two nearby clusters of galaxies, A194 (
$z = 0.018$
) and A1060 (
$z = 0.0114$
), have been analyzed for their X-ray point-source properties with XMM-Newton EPIC-PN data. A multi-band source ...detection technique was applied to both of the clusters, resulting in 46 sources from the A194 field and 32 sources from the A1060 field, respectively. The cumulative
$\log (N) \hbox{--} \log(S)$
for a flux limit of
$F_{\mathrm{X}} \geq 1 \times 10^{-14} \,\mathrm{erg} \,\mathrm{cm}^{-2} \,\mathrm{s}^{-1}$
was calculated and compared with that of the Lockman Hole. A
$\sim 3\,\sigma$
excess of X-ray sources was found for the cluster regions. Considering the higher fraction observed in optical studies from the clusters, we estimate that the cluster source density is 6-times higher than the blank-field source density, and 15-times higher than the local group. Our X-ray selected sources have luminosity values of
$10^{39.6} \leq L_{\mathrm{X}} \leq 10^{41.4} \,\mathrm{erg} \,\mathrm{s}^{-1}$
, in which X-ray emission from LMXBs, hot halos and starburst galaxies becomes noticeable. The significance of the source-density excess gradually vanishes for sources with
$L_{\mathrm{X}} \geq 10^{40.5} \,\mathrm{erg} \,\mathrm{s}^{-1}$
, at which point the source density becomes comparable to that of the blank-field level. Considering this confined low-luminosity range and the X-ray to optical luminosity ratios (
$L_{\mathrm{X}} / L_{\mathrm{B}}$
), the observed overdensity is ascribed to AGN fueling by its infall into cluster environment for
$L_{\mathrm{X}} \leq 10^{40.5} \,\mathrm{erg} \,\mathrm{s}^{-1}$
in the X-ray luminosity function. However, the quenching of AGN activity by the deep cluster potential explains why the excess of the source density vanishes for brighter sources.
PDF
