325 research outputs found
Suzaku Detection of Thermal X-Ray Emission Associated with the Western Radio Lobe of Fornax A
We present the results of X-ray mapping observations of the western radio
lobe of the Fornax A galaxy, using the X-ray Imaging Spectrometer (XIS) onboard
the Suzaku satellite with a total exposure time of 327 ks. The purpose of this
study is to investigate the nature and spatial extent of the diffuse thermal
emission around the lobe by exploiting the low and stable background of the
XIS. The diffuse thermal emission had been consistently reported in all
previous studies of this region, but its physical nature and relation to the
radio lobe had not been examined in detail. Using the data set covering the
entire western lobe and the central galaxy NGC 1316, as well as comparison sets
in the vicinity, we find convincingly the presence of thermal plasma emission
with a temperature of ~1 keV in excess of conceivable background and
contaminating emission (cosmic X-ray background, Galactic halo, intra-cluster
gas of Fornax, interstellar gas of NGC 1316, and the ensemble of point-like
sources). Its surface brightness is consistent with having a spherical
distribution peaking at the center of the western lobe with a projected radius
of ~12 arcmin. If the volume filling factor of the thermal gas is assumed to be
unity, its estimated total mass amounts to ~10^{10} M_sun, which would be
~10^{2} times that of the central black hole and comparable to that of the
current gas mass of the host galaxy. Its energy density is comparable to or
larger than those in the magnetic field and non-thermal electrons responsible
for the observed radio and X-ray emission.Comment: 10 pages, 5 figures, accepted for publication in PAS
ASCA Observations of Two Ultra-Luminous Compact X-Ray Sources in the Edge-on Spiral Galaxy NGC 4565
The edge-on spiral galaxy NGC 4565 was observed for 35 ks with ASCA in
the 0.5-10 keV energy band. The X-ray emission was dominated by two bright
sources, which can be identified with two point-like X-ray sources seen in the
ROSAT HRI image. The observed 0.5-10 keV fluxes of these sources, and , % % imply bolometric
luminosities of and ,
respectively. They exhibit similar spectra, which can be explained by emission
from optically thick accretion disks with the inner disk temperature of 1.4-1.6
keV. One of them, coincident in position with the nucleus, shows too low
absorption to be the active nucleus seen through the galaxy disk. Their spectra
and high luminosities suggest that they are both mass accreting black hole
binaries. However the black-hole mass required by the Eddington limit is rather
high (), and the observed disk temperature is too high to be
compatible with the high black-hole mass. Several attempts are made to solve
these problesms.Comment: 20page
Hard X-Ray Spectrum from West Lobe of Radio Galaxy Fornax A Observed with Suzaku
An observation of the West lobe of radio galaxy Fornax A (NGC 1316) with
Suzaku is reported. Since Feigelson et al. (1995) and Kaneda et al. (1995)
discovered the cosmic microwave background boosted inverse-Comptonized (IC)
X-rays from the radio lobe, the magnetic field and electron energy density in
the lobes have been estimated under the assumption that a single component of
the relativistic electrons generates both the IC X-rays and the synchrotron
radio emission. However, electrons generating the observed IC X-rays in the 1
-- 10 keV band do not possess sufficient energy to radiate the observed
synchrotron radio emission under the estimated magnetic field of a few micro-G.
On the basis of observations made with Suzaku, we show in the present paper
that a 0.7 -- 20 keV spectrum is well described by a single power-law model
with an energy index of 0.68 and a flux density of 0.12+/-0.01 micro-Jy at 1
keV from the West lobe. The derived multiwavelength spectrum strongly suggests
that a single electron energy distribution over a Lorentz factor gamma = 300 -
90000 is responsible for generating both the X-ray and radio emissions. The
derived physical quantities are not only consistent with those reported for the
West lobe, but are also in very good agreement with those reported for the East
lobe.Comment: 8 pages, 6 figures; accepted for publication in PASJ (Publications of
the Astronomical Society of Japan) Suzaku 3rd special issue: TYPOS in flux
density unit were correcte
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