817 research outputs found
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
X-ray Observation of Mars with Suzaku at Solar Minimun
Mars was observed in X-rays during April 3-5 2008 for 82 ksec with the
Japanese Suzaku observatory. Mars has been known to emit X-rays via the
scattering of solar X-rays and via the charge exchange between neutral atoms in
the exosphere and solar wind ions. Past theoretical studies suggest that the
exospheric neutral density may vary by a factor of up to 10 over the solar
cycle. To investigate a potential change of the exospheric charge exchange
emission, Mars was observed with Suzaku at solar minimum. Significant signals
were not detected at the position of Mars in the energy band of 0.2-5 keV. A 2
sigma upper limit of the O VII line flux in 0.5-0.65 keV was 4.3
ph cm s. Comparing this upper limit to the past Chandra and
XMM-Newton observations conducted near solar maximum, it was found that the
exospheric density at solar minimum does not exceed that near solar maximum by
more than 6-70 times.Comment: 17 pages, 7 figures, accepted for publication in PAS
On the Electric Field due to Tides
It has been pointed out that one of the main causes of faults on submarine cables would be the electrolytic corrosion due to the current which is induced in the cable by tides moving across the earth's magnetic field. In this paper, some formulas for electric field due to a stream of water which flows in a tide-way of rectangular cross-section are derived, and results of numerical computations are shown. The effects of conductivity of the bottom are also treated as boundary value problems. It is found that the sides of tide-way are the most dangerous places as the intense electrolytic corrosion of cable occurs there
Enhancement of Terrestrial Diffuse X-ray Emission Associated With Coronal Mass Ejection and Geomagnetic Storm
We present an analysis of a Suzaku observation taken during the geomagnetic
storm of 2005 August 23-24. We found time variation of diffuse soft X-ray
emission when a coronal mass ejection hit Earth and caused a geomagnetic storm.
The diffuse emission consists of fluorescent scattering of solar X-rays and
exospheric solarwind charge exchange. The former is characterized by a neutral
oxygen emission line due to strong heating of the upper atmosphere during the
storm time, while the latter is dominated by a sum of C V, C VI, N VI, N VII, O
VII, and O VIII emission lines due to the enhanced solar wind flux in the
vicinity of the exosphere. Using the solar wind data taken with the ACE and
WIND satellites,a time correlation between the solar wind and the strong O VII
line flux were investigated. We estimated necessary column densities for the
solar X-ray scattering and exospheric SWCX. From these results, we argue that a
part of the solar wind ions enter inside the magnetosphere and cause the SWCX
reaction.Comment: 33 pages, 16 figures, accepted for publication in PAS
Iron Emission Lines on the Galactic Ridge Observed with Suzaku
In order to elucidate origin of the Galactic Ridge X-ray Emission, we
analyzed Suzaku data taken at various regions along the Galactic plane and
studied their Fe-K emission line features. Suzaku resolved the Fe line complex
into three narrow lines at ~6.4 keV,~6.7 keV and ~6.97 keV, which are K-lines
from neutral (or low-ionized), He-like, and H-like iron ions, respectively. The
6.7 keV line is clearly seen in all the observed regions and its longitudinal
distribution is consistent with that determined from previous observations. The
6.4 keV emission line was also found in various Galactic plane regions (b~0).
Differences in flux ratios of the 6.4 keV/6.7 keV and 6.97 keV/6.7 keV lines
between the Galactic plane and the Galactic center regions are studied and its
implication is discussed.Comment: Accepted for publication in PASJ Suzaku 3rd special issu
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