318 research outputs found
X-ray measurement of electron and magnetic-field energy densities in the west lobe of the giant radio galaxy 3C 236
X-ray emission associated with the west lobe of the giant radio galaxy, 3C
236, was investigated with the Suzaku observatory, to evaluate the energetics
in the lobe. After removing contamination from X-ray sources detected with
Chandra and subtracting the X-ray and non-X-ray backgrounds, the Suzaku
spectrum from the lobe was reproduced by a power-low model with a photon index
of where the first and second errors
represent the statistical and systematic ones, respectively. Within the errors,
the X-ray index was consistent with the radio synchrotron one, , estimated in the 326 -- 2695 MHz range. This agreement
supports that the X-ray emission is attributed to the inverse-Compton (IC)
radiation from the synchrotron electrons filling the lobe, where the cosmic
microwave background photons are up-scattered. This result made 3C 236 the
largest radio galaxy, of which the lobe has ever been probed through the IC
X-ray photons. When the photon index was fixed at , the X-ray
flux density at 1 keV was measured as nJy. A
comparison of the X-ray flux to the radio one ( Jy
at 608.5 MHz) yields the energy densities of the electrons and magnetic field
in the west lobe as
ergs cm and ergs cm, respectively, indicating a mild electron dominance of . The latter corresponds to the
magnetic field strength of G.These
are typical among the lobes of giant radio galaxies. A compilation of the
-size relation for the IC-detected radio galaxies implies that the
west lobe of 3C 236 is still actively energized by its jet.Comment: Accepted for PASJ, 9 figures, 7 table
Mass Function of Binary Massive Black Holes in Active Galactic Nuclei
If the activity of active galactic nuclei (AGNs) is predominantly induced by
major galaxy mergers, then a significant fraction of AGNs should harbor binary
massive black holes in their centers. We study the mass function of binary
massive black holes in nearby AGNs based on the observed AGN black-hole mass
function and theory of evolution of binary massive black holes interacting with
a massive circumbinary disk in the framework of coevolution of massive black
holes and their host galaxies. The circumbinary disk is assumed to be steady,
axisymmetric, geometrically thin, self-regulated, self-gravitating but
non-fragmenting with a fraction of Eddington accretion rate, which is typically
one tenth of Eddington value. The timescale of orbital decay is {then}
estimated as ~10^8yr for equal mass black-hole, being independent of the black
hole mass, semi-major axis, and viscosity parameter but dependent on the
black-hole mass ratio, Eddington ratio, and mass-to-energy conversion
efficiency. This makes it possible for any binary massive black holes to merge
within a Hubble time by the binary-disk interaction. We find that (1.8+-0.6%)
for the equal mass ratio and (1.6+-0.4%) for the one-tenth mass ratio of the
total number of nearby AGNs have close binary massive black holes with orbital
period less than ten years in their centers, detectable with on-going highly
sensitive X-ray monitors such as Monitor of All-sky X-ray Image and/or
Swift/Burst Alert Telescope. Assuming that all binary massive black holes have
the equal mass ratio, about 20% of AGNs with black hole masses of
10^{6.5-7}M_sun has the close binaries and thus provides the best chance to
detect them.Comment: 22 pages, 11 figures, accepted for publication in PASJ. The draft was
significantly revised. The major differences from the previous version are as
follows: (1)The circumbinary disk is assumed to be a steady, axisymmetric,
geometrically thin, self-gravitating, self-regulated but non-fragmenting.
(2)The stellar scattering process is taken account of in the merging process
of binary black hole
Suzaku investigation into the nature of the nearest ultraluminous X-ray source, M33 X-8
The X-ray spectrum of the nearest ultraluminous X-ray source, M33 X-8,
obtained by Suzaku during 2010 January 11 -- 13, was closely analyzed to
examine its nature. It is, by far, the only data with the highest signal
statistic in 0.4 -- 10 keV range. Despite being able to reproduce the X-ray
spectrum, Comptonization of the disk photons failed to give a physically
meaningful solution. A modified version of the multi-color disk model, in which
the dependence of the disk temperature on the radius is described as r^(-p)
with p being a free parameter, can also approximate the spectrum. From this
model, the innermost disk temperature and bolometric luminosity were obtained
as T_in = 2.00-0.05+0.06 keV and L_disk = 1.36 x 10^39 (cos i)^(-1) ergs/s,
respectively, where i is the disk inclination. A small temperature gradient of
p = 0.535-0.005+0.004, together with the high disk temperature, is regarded as
the signatures of the slim accretion disk model, suggesting that M33 X-8 was
accreting at high mass accretion rate. With a correction factor for the slim
disk taken into account, the innermost disk radius, R_in =81.9-6.5+5.9 (cos
i)^(-0.5) km, corresponds to the black hole mass of M \sim 10 M_sun (cos
i)^(-0.5). Accordingly, the bolometric disk luminosity is estimated to be about
80 (cos i)^(-0.5)% of the Eddington limit. A numerically calculated slim disk
spectrum was found to reach a similar result. Thus, the extremely
super-Eddington luminosity is not required to explain the nature of M33 X-8.
This conclusion is utilized to argue for the existence of intermediate mass
black holes with M > 100 M_sun radiating at the sub/trans-Eddington luminosity,
among ultraluminous X-ray sources with L_disk > 10^(40) ergs/s.Comment: 10 pages, 4 figures, PASJ accepte
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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