745 research outputs found
X-Ray Evidence of an AGN in M82
An X-ray spectrum of the famous starburst galaxy M82 consists of three
components: soft, medium, and hard components (Tsuru et al. 1997). The spectrum
of the hard component, which is spatially unresolved, is well represented by an
absorbed thermal bremsstrahlung, or an absorbed power-law model. However the
origin of the hard component was unclear. Thus, we made a monitoring
observation with ASCA in 1996. Although the X-ray flux of the soft and medium
components remained constant, a significant time variability of the hard
component was found between erg/s and erg/s
at various time scales from 10 ks to a month. The temperature or photon index
of the hard component also changed. We proved that the spatial position of the
hard component is the center of M82. The spectrum of the variable source
obtained by subtracting the spectrum of the lowest state from the highest state
suggests the strong absorption of cm, which means
the variable source is embedded in the center of M82. All these suggest that a
low-luminosity AGN exists in M82.Comment: 15pages for text and tables. 13pages for figure
The X-ray Structure of A399 and A401: A Pre-Merging Cluster Pair
We present {\em ASCA} results of the pair clusters A399 and A401. The region
between the two clusters exhibits excess X-rays over the value expected with a
simple superposition of the two clusters. We see, however, no temperature rise
at the merging front; the temperature is near the average of those in the inner
regions of the two clusters. These indicate that the two clusters are really
interacting but it is not strong at present.
The inner regions of the two clusters show no radial variations of
temperature, abundance and absorption values. We set upper-limits of mass
deposition rate of cooling flow to be and
for A399 and A401, respectively. A hint of
azimuthal variation of the temperature is also found.Comment: 17 pages, 13 postscript figures, 2 external tables, accepted for
publication in PAS
ASCA observations of massive medium-distant clusters of galaxies. II
We have selected seven medium-distant clusters of galaxies (z ~ 0.1 - 0.3)
for multi-wavelength observations with the goal of investigating their
dynamical state. Following Paper I (Pierre et al. 1999) which reported the ASCA
results about two of them, we present here the analysis of the ASCA
observations of the other five clusters; RXJ1023.8-2715 (A3444),
RXJ1031.6-2607, RXJ1050.5-0236 (A1111), RXJ1203.2-2131(A1451), and
RXJ1314.5-2517. Except for RXJ1031.6, whose X-ray emission turned out to be
dominated by an AGN, the ASCA spectra are well fitted by a one-temperature thin
thermal plasma model. We compare the temperature-luminosity relation of our
clusters with that of nearby ones (z<0.1). Two clusters, RXJ1050.5 and
RXJ1023.8, show larger luminosities than the bulk of clusters at similar
temperatures, which suggests the presence of a cooling flow. The temperature
vs. iron-abundance relationship of our sample is consistent with that of nearby
clusters.Comment: 9 pages, 20 figures, A&AS in pres
An Analysis of \pi\pi-Scattering Phase Shift and Existence of \sigma(555) particle
In most of the Nambu:Jona-Lasinio(NJL)-type models, realizing the hidden
chiral symmetry, the existence of a scalar particle \sigma is needed with a
mass m_\sigma=2 m_q, as a partner of the Nambu-Goldstone boson \pi. However,
the results of many analyses on \pi\pi phase-shift thus far made have been
negative for its existence. In this paper we re-analyze the phase-shift,
applying a new method, the interfering amplitude method, which treats the
T-matrix directly and describes multi-resonances in conformity with the
unitarity. As a result, the existence of \sigma has been strongly suggested
from the behavior of the \pi\pi-->\pi\pi phase shift between the \pi\pi- and
the KK- thresholds, with mass = 553.3 +- 0.5_{st} MeV and width= 242.6 +-
1.2_{st} MeV. The most crucial point in our analysis is the introduction of a
negative background phase, possibly reflecting a ``repulsive core" in \pi\pi
interactions. The properties of f_0(980) are also investigated from data
including those over the KK threshold. Its mass is obtained as 993.2 +-
6.5_{st} +- 6.9_{sys} MeV. Its width is about a hundred MeV, although this
depends largely on the treatment of the elasticity and the \pi\pi-->KK phase
shift, both of which may have large experimental uncertainties.Comment: 22 pages, Latex with Prog. Theor. Phys. format PTPTEX.sty, 4 EPS
figure
Discovery of the compact X-ray source inside the Cygnus Loop
We detected an X-ray compact source inside the Cygnus Loop during the
observation project of the whole Cygnus Loop with the ASCA GIS. The source
intensity is 0.11 c s for GIS and 0.15 c s for SIS, which is the
strongest in the ASCA band. The X-ray spectra are well fitted by a power law
spectrum of a photon index of \error{-2.1}{0.1} with neutral H column of
(\error{3.1}{0.6}). Taking into account the
interstellar absorption feature, this source is X-ray bright mainly above 1 keV
suggesting either an AGN or a rotating neutron star. So far, we did not detect
intensity variation nor coherent pulsation mainly due to the limited
observation time. There are several optical bright stellar objects within the
error region of the X-ray image. We carried out the optical spectroscopy for
the brightest source (V=+12.6) and found it to be a G star. The follow up deep
observation both in optical and in X-ray wavelengths are strongly required.Comment: Accepted for Publications of the Astronomical Society of Japan 17
pages, 3 figur
Suzaku Observation of HESS J1825-137: Discovery of Largely-Extended X-rays near from PSR J1826-1334
We observed the brightest part of HESS J1825-137 with the Suzaku XIS, and
found diffuse X-rays extending at least up to 15' (~ 17 pc) from the pulsar PSR
J1826-1334. The spectra have no emission line, and are fitted with an absorbed
power-law model. The X-rays, therefore, are likely due to synchrotron emission
from a pulsar wind nebula. The photon index near at the pulsar (r<1.5') is 1.7
while those in r=1.5-16 are nearly constant at Gamma=2.0. The spectral energy
distribution of the Suzaku and H.E.S.S. results are naturally explained by a
combined process; synchrotron X-rays and gamma-rays by the inverse Compton of
the cosmic microwave photons by high-energy electrons in a magnetic field of 7
micro G. If the electrons are accelerated at the pulsar, the electrons must be
transported over 17 pc in the synchrotron life time of 1900 yr, with a velocity
of > 8.8 times 10^3 km s^{-1}.Comment: 9 pages, 10 figure
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