2,583 research outputs found
The variable OVIII Warm Absorber in MCG-6-30-15
We present the results of a 4 day ASCA observation of the Seyfert galaxy
MCG-6-30-15, focussing on the nature of the X-ray absorption by the warm
absorber, characterizd by the K-edges of the intermediately ionized oxygen,
OVII and OVIII. We confirm that the column density of OVIII changes on a
timescale of ~s when the X-ray continuum flux decreases. The
significant anti-correlation of column density with continuum flux gives direct
evidence that the warm absorber is photoionized by the X-ray continuum. From
the timescale of the variation of the OVIII column density, we estimate that it
originates from gas within a radius of about 10^{17}\cm of the central
engine. In contrast, the depth of the OVII edge shows no response to the
continuum flux, which indicates that it originates in gas at larger radii. Our
results strongly suggest that there are two warm absorbing regions; one located
near or within the Broad Line Region, the other associated with the outer
molecular torus, scattering medium or Narrow Line Region.Comment: 8 pages (including figures) uuencoded gziped PS file. Submitted to
Publications of the Astronomical Society of Japa
Properties of 10 (18)-10 (19)eV EAS at far core distance
The properties of 10 to the 18th power - 10 to the 19th power eV EAS showers such as the electron lateral distribution, the muon lateral distribution ( 1Gev), the ratio of muon density to a electron density, the shower front structure and the transition effects in scintillator of 5cm thickness are investigated with the Akeno 4 sq km/20sq km array at far core distances between 500m and 3000m. The fluctuation of densities and arrival time increase rapidly at core distances greater than 2km
Akeno 20 km (2) air shower array (Akeno Branch)
As the first stage of the future huge array, the Akeno air shower array was expanded to about 20 sq. km. by adding 19 scintillation detectors of 2.25 sq m area outside the present 1 sq. km. Akeno array with a new data collection system. These detectors are spaced about 1km from each other and connected by two optical fiber cables. This array has been in partial operation from 8th, Sep. 1984 and full operation from 20th, Dec. 1984. 20 sq m muon stations are planned to be set with 2km separation and one of them is now under construction. The origin of the highest energy cosmic rays is studied
Properties of the Brightest Cluster Galaxy and Its Host Cluster
We investigate the relation between the properties of Brightest Cluster
Galaxies (BCGs) and those of their host clusters. To quantify the properties of
cluster hot gas, we employ the parameter of the fundamental plane of X-ray
clusters. It is found that the offset of the BCG from the peak of cluster X-ray
emission is larger for smaller clusters. The parameter (not the
redshift {\it z}), which mainly depends on virial density ,
is considered to represent the formation epoch of a cluster. We thus consider
that the offset of the BCG is correlated with the dynamical equilibrium state
of its host cluster. On the contrary, no significant correlation is found
between the absolute optical magnitude of the BCG and the parameter . If the
extreme brightness of the BCG is mainly acquired in the course of cluster
evolution by environmental effect, BCGs are expected to be brighter in large
clusters. Our result is not consistent with this simplified view. On the
contrary, it is possible that the extreme brightness of the BCG is likely to be
determined in the early history of cluster collapse.Comment: 18 pages, 9 figures, accepted for publication in Ap
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
Growth hormone response to growth hormone-releasing peptide-2 in growth hormone-deficient Little mice
OBJECTIVE: To investigate a possible direct, growth hormone-releasing, hormone-independent action of a growth hormone secretagogue, GHRP-2, in pituitary somatotroph cells in the presence of inactive growth hormonereleasing hormone receptors. MATERIALS AND METHODS: The responses of serum growth hormone to acutely injected growth hormone-releasing P-2 in lit/litmice, which represent a model of GH deficiency arising frommutated growth hormone-releasing hormonereceptors, were compared to those observed in the heterozygous (lit/+) littermates and wild-type (+/+) C57BL/6J mice. RESULTS: After the administration of 10 mcg of growth hormone-releasing P-2 to lit/lit mice, a growth hormone release of 9.3±1.5 ng/ml was observed compared with 1.04±1.15 ng/ml in controls (p<0.001). In comparison, an intermediate growth hormone release of 34.5±9.7 ng/ml and a higher growth hormone release of 163±46 ng/ml were induced in the lit/+ mice and wild-type mice, respectively. Thus, GHRP-2 stimulated growth hormone in the lit/lit mice, and the release of growth hormone in vivo may be only partially dependent on growth hormone-releasing hormone. Additionally, the plasma leptin and ghrelin levels were evaluated in the lit/lit mice under basal and stimulated conditions. CONCLUSIONS: Here, we have demonstrated that lit/lit mice, which harbor a germline mutation in the Growth hormone-releasing hormone gene, maintain a limited but statistically significant growth hormone elevation after exogenous stimulation with GHRP-2. The present data probably reflect a direct, growth hormone-independent effect on Growth hormone S (ghrelin) stimulation in the remaining pituitary somatotrophs of little mice that is mediated by growth hormone S-R 1a
Space Tethers: Design Criteria
This document is prepared to provide a systematic process for the selection of tethers for space applications. Criteria arc provided for determining the strength requirement for tether missions and for mission success from tether severing due to micrometeoroids and orbital debris particle impacts. Background information of materials for use in space tethers is provided, including electricity-conducting tethers. Dynamic considerations for tether selection is also provided. Safety, quality, and reliability considerations are provided for a tether project
Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff
The cosmic-ray energy spectrum above 10^{18.5} eV is reported using the
updated data set of the Akeno Giant Air Shower Array (AGASA) from February 1990
to October 1997. The energy spectrum extends beyond 10^{20} eV and the energy
gap between the highest energy event and the others is being filled up with
recently observed events. The spectral shape suggests the absence of the 2.7 K
cutoff in the energy spectrum or a possible presence of a new component beyond
the 2.7 K cutoff.Comment: to be published in PRL, 3 figures, REVTEX forma
Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei
In this article we examine the hypothesis that the highest energy cosmic rays
are complex nuclei from extragalactic sources. Under reasonable physical
assumptions, we show that the nearby metally rich starburst galaxies (M82 and
NGC 253) can produce all the events observed above the ankle. This requires
diffusion of particles below eV in extragalactic magnetic fields nG. Above eV, the model predicts the presence of
significant fluxes of medium mass and heavy nuclei with small rate of change of
composition. Notwithstanding, the most salient feature of the
starburst-hypothesis is a slight anisotropy induced by iron debris just before
the spectrum-cutoff.Comment: To appear in Phys. Rev. D, reference adde
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