1,195 research outputs found
Matter content in AGN jets: constraint from cocoon dynamics?
The matter content of jets in active galactic nuclei is examined in a new
way. We model the dynamical expansion of its cocoon embedded in the
intra-cluster medium (ICM). By comparing the observed shape of the cocoon with
that expected from the theoretical model, we estimate the total pressure
() and electron temperature () of the cocoon. The number
density of the total electrons () is constrained by using the
non-thermal spectrum of the hot spot and the analysis of the momentum balance
between the jet thrust and the rum pressure of ICM. Together with the obtained
, and , we constrain the matter content in the
jets. We find that, in the case of Cygnus A, the ratio of number density of
protons to that of electrons is of order of . This implies the
existence of a large number of positron in the jet.Comment: 4 pages, to appear in the proceedings of "Astrophysical Sources of
High Energy Particles and Radiation", Torun, 20-24 June 200
Evolution of non-thermal emission from shell associated with AGN jets
We explore the evolution of the emissions by accelerated electrons in shocked
shells driven by jets in active galactic nuclei (AGNs). Focusing on powerful
sources which host luminous quasars, we evaluated the broadband emission
spectra by properly taking into account adiabatic and radiative cooling effects
on the electron distribution. The synchrotron radiation and inverse Compton
(IC) scattering of various photons that are mainly produced in the accretion
disc and dusty torus are considered as radiation processes. We show that the
resultant radiation is dominated by the IC emission for compact sources (<
10kpc), whereas the synchrotron radiation is more important for larger sources.
We also compare the shell emissions with those expected from the lobe under the
assumption that a fractions of the energy deposited in the shell and lobe
carried by the non-thermal electrons are and
, respectively. Then, we find that the shell
emissions are brighter than the lobe ones at infra-red and optical bands when
the source size is > 10kpc, and the IC emissions from the shell at > 10 GeV can
be observed with the absence of contamination from the lobe irrespective of the
source size. In particular, it is predicted that, for most powerful nearby
sources (), TeV gamma-rays produced via the IC
emissions can be detected by the modern Cherenkov telescopes such as MAGIC,
HESS and VERITAS.Comment: 13 pages, 5 figures, accepted for publication in Ap
Two-band Fluctuation Exchange Study on the Superconductivity of -(BEDT-TTF)ICl under High Pressure
We study the pressure dependence of the superconducting transition
temperature of an organic superconductor -(BEDT-TTF)ICl by
applying the fluctuation exchange method to the Hubbard model on the original
two-band lattice at 3/4-filling rather than the single band model in the strong
dimerization limit. Our study is motivated by the fact that hopping parameters
evaluated from a first-principles study suggest that the dimerization of the
BEDT-TTF molecules is not so strong especially at high pressure. Solving the
linearized Eliashberg's equation, a d-wave-like superconducting state
with realistic values of is obtained in a pressure regime somewhat higher
than the actual experimental result. These results are similar to those
obtained within the single band model in the previous study by Kino {\it et
al}. We conclude that the resemblance to the dimer limit is due to a
combination of a good Fermi surface nesting, a large density of states near the
Fermi level, and a moderate dimerization, which cooperatively enhance electron
correlation effects and also the superconducting .Comment: 6 pages, 8 figure
Phase Diagram of -(BEDT-TTF)ICl under High Pressure Based on the First-Principles Electronic Structure
We present a theoretical study on the superconductivity of
-(BEDT-TTF)ICl at 14.2 K under a high hydrostatic
pressure recently found, which is the highest among organic superconductors. In
the present work, we study an effective model using the fluctuation-exchange
(FLEX) approximation based on the results of first-principles calculation. In
the obtained phase diagram, the superconductivity with -like symmetry
is realized next to the antiferromagnetic phase, as a result of the
one-dimensional to two-dimensional crossover driven by the pressure.Comment: 4 pages, 3 figures. accepted for publication in J. Phys. Soc. Jpn.
errors correcte
Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance
It is proposed that the presence of a tilted and anisotropic Dirac cone can
be verified using the interlayer magnetoresistance in the layered Dirac fermion
system, which is realized in quasi-two-dimensional organic compound
\alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic
Landau level wave functions and assuming local tunneling of electrons. It is
shown that the resistivity takes the maximum in the direction of the tilt if
anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is
described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.
Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction
The spatial charge arrangement of a typical quasi-two-dimensional organic
conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis
using synchrotron radiation. The results show that the horizontal stripe type
structure, which was suggested by mean field theory, is established. We also
find the charge disproportion above the metal-insulator transition temperature
and a significant change in transfer integrals caused by the phase transition.
Our result elucidates the insulating phase of this material as a 2k_F charge
density localization.Comment: 8 pages, 5 figures, 1 tabl
New prediction of extragalactic GeV gamma-ray emission from radio lobes of young AGN jets
We present a new prediction of GeV -ray emission from radio lobes of
young AGN jets. In the previous work of Kino et al. (2007), MeV -ray
bremsstrahlung emission was predicted from young cocoons/radio-lobes in the
regime of no coolings. In this study, we include cooling effects of
bremsstrahlung emission and adiabatic loss. With the initial conditions
determined by observed young radio lobes, we solve a set of equations
describing the expanding lobe evolution. Then we find that the lobes initially
have electron temperature of GeV, and they cool down to MeV by the
adiabatic loss. Correspondingly, the lobes initially yield bright
bremsstrahlung luminosity in GeV range and they fade out. We estimate
these -ray emissions and show that nearby young radio lobes could be
detected with Fermi Gamma-ray Space Telescope.Comment: 5 pages, 3 figures, MNRAS Letters, accepte
Possible high superconductivity mediated by antiferromagnetic spin fluctuations in systems with Fermi surface pockets
We propose that if there are two small pocket-like Fermi surfaces, and the
spin susceptibility is pronounced around a wave vector {\bf Q} that bridges the
two pockets, the spin-singlet superconductivity mediated by spin fluctuations
may have a high transition temperature. Using the fluctuation exchange
approximation, this idea is confirmed for the Hubbard on a lattice with
alternating hopping integrals, for which is estimated to be almost an
order of magnitude larger than those for systems with a large connected Fermi
surface.Comment: 5 pages, uses RevTe
Extragalactic MeV gamma-ray emission from cocoons of young radio galaxies
Strong -ray emission from cocoons of young radio galaxies is newly
predicted. Considering the process of adiabatic injection of the shock
dissipation energy and mass of the relativistic jet in active nuclei (AGNs)
into the cocoon, while assuming thermalizing electron plasma interactions, we
find that the thermal electron temperature of the cocoon is typically predicted
in MeV, which is determined only by the bulk Lorentz factor of the
relativistic jet. Together with the time-dependent dynamics of the cocoon
expansion, we find that young cocoons can yield thermal bremsstrahlung
emissions at energies MeV.Comment: 5pages, 1figure, MNRAS accepte
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