Prog. Theor. Phys. Supplement No.143 (2001) pp. 99-113
Highlights of X-Ray Astronomy Mainly Based on ASCA Results
Institute of Space and Astronautical Science, Sagamihara 229-8510, Japan
(Received May 7, 2001)
I present three topics of X-ray astronomy to which ASCA
has made significant contributions.
The first one is X-ray observations to explore sites of particle acceleration
in our Galaxy: A discovery of clear evidence for electrons to be
accelerated up to
∼100 TeV in SN1006 by ASCA, and an interesting problem
on the energy source of the Galactic ridge X-ray emission are shown.
The second topic is on ultra-luminous binary X-ray sources.
ASCA observations of several point sources with X-ray
luminosities of 1039 - 40 erg/s
in nearby spiral galaxies showed that their X-ray spectra
were commonly reproduced by a two-component-model composing of
a so-called disk black-body component and a power-law component.
This strongly suggests that these sources are binary sources containing
black holes with the mass close to 100 M⊙.
An interesting result of spectral fits of the two-component-model to
the observed spectra
is that the innermost radius of the disk seems to be so small as to
indicate for the central objects to be Kerr black holes.
On the other hand, detailed analyses of X-ray spectrum of the Galactic
superluminal source, GRS 1915 + 105 showed that
the innermost radius of this source also becomes very small but that
it does not always happen.
In this source, the disk seems to change its state between a high temperature
(small radius) state and a low temperature (large radius) state.
According to theoretical study of accretion disks, these two states
can be considered to
correspond to a so-called slim disk and a standard disk, respectively.
The third topic is on a broad and skewed feature around 5 – 7 keV in spectra
of Seyfert galaxies. It was first discovered from MCG-6-30-15
and is one of the most remarkable results with ASCA.
The profile is well interpreted by the so-called “disk-line" model,
in which the feature is considered to be iron fluorescent lines coming
from an innermost
region of a relatively cool disk and to be broadened and skewed
by the relativistic motion of the matter as well as by the general
in the vicinity of the central black hole.
However, analyses of long observations of MCG-6-30-15
and NGC4151 show that
the time variability of the flux and profile of the “disk-line"
feature rather prefer alternative interpretations
to the “disk-line" model.
DOI : 10.1143/PTPS.143.99
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Citing Article(s) :
Progress of Theoretical Physics Supplement No.169 (2007) pp. 131-135
Continuum and Line Emissions from the Galactic Ridge and Clusters: Problems of Interpretation and Ways of Solution
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