123 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
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
WIDGET: System Performance and GRB Prompt Optical Observations
The WIDeField telescope for Gamma-ray burst Early Timing (WIDGET) is used for
a fully automated, ultra-wide-field survey aimed at detecting the prompt
optical emission associated with Gamma-ray Bursts (GRBs). WIDGET surveys the
HETE-2 and Swift/BAT pointing directions covering a total field of view of 62
degree x 62 degree every 10 secounds using an unfiltered system. This
monitoring survey allows exploration of the optical emission before the
gamma-ray trigger. The unfiltered magnitude is well converted to the SDSS r'
system at a 0.1 mag level. Since 2004, WIDGET has made a total of ten
simultaneous and one pre-trigger GRB observations. The efficiency of
synchronized observation with HETE-2 is four times better than that of Swift.
There has been no bright optical emission similar to that from GRB 080319B. The
statistical analysis implies that GRB080319B is a rare event. This paper
summarizes the design and operation of the WIDGET system and the simultaneous
GRB observations obtained with this instrument.Comment: 19 pages, 11 figures, Accepted to appear in PAS
Suzaku diagnostics of the energetics in the lobes of the giant radio galaxy 3C 35
The Suzaku observation of a giant radio galaxy 3C 35 revealed faint extended
X-ray emission, associated with its radio lobes and/or host galaxy. After
careful subtraction of the X-ray and non-X-ray background and contaminating
X-ray sources, the X-ray spectrum of the faint emission was reproduced by a sum
of the power-law (PL) and soft thermal components. The soft component was
attributed to the thermal plasma emission from the host galaxy. The photon
index of the PL component,
where the first and second errors represent the statistical and systematic
ones, was found to agree with the synchrotron radio index from the lobes,
. Thus, the PL component was attributed to the inverse
Compton (IC) X-rays from the synchrotron electrons in the lobes. The X-ray flux
density at 1 keV was derived as nJy with the photon
index fixed at the radio value. The X-ray surface brightness from these lobes
( nJy arcmin) is lowest among the lobes studied through the IC
X-ray emission. In combination with the synchrotron radio flux density, Jy at 327.4 MHz, the electron energy density spatially averaged over
the lobes was evaluated to be the lowest among those radio galaxies, as ergs cm over the
electron Lorentz factor of -- . The magnetic energy density
was calculated as ergs cm, corresponding to the magnetic field strength of
G. These results suggest that the
energetics in the 3C 35 lobes are nearly consistent with equipartition between
the electrons and magnetic fields.Comment: 10 pages, 8 figures, accepted for Ap
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