1,873 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
Hydrodynamics of Internal Shocks in Relativistic Outflows
We study the hydrodynamical effects of two colliding shells, adopted to model
internal shocks in various relativistic outflows such as gamma-ray bursts and
blazars. We find that the density profiles are significantly affected by the
propagation of rarefaction waves. A split-feature appears at the contact
discontinuity of the two shells. The shell spreading with a few ten percent of
the speed of light is also shown to be a notable aspect. The conversion
efficiency of the bulk kinetic energy to internal one shows deviations from the
widely-used inelastic two-point-mass-collision model. Observational
implications are also shortly discussed.Comment: 6 pages, 4 figures, Proceeding of International Symposium on High
Energy Gamma-ray Astronomy (July 26-30, 2004, Heidelberg, Germany
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
Hydrodynamical effects in internal shock of relativistic outflows
We study both analytically and numerically hydrodynamical effects of two
colliding shells, the simplified models of the internal shock in various
relativistic outflows such as gamma-ray bursts and blazars. We pay particular
attention to three interesting cases: a pair of shells with the same rest mass
density (``{\it equal rest mass density}''), a pair of shells with the same
rest mass (``{\it equal mass}''), and a pair of shells with the same bulk
kinetic energy (``{\it equal energy}'') measured in the intersteller medium
(ISM) frame. We find that the density profiles are significantly affected by
the propagation of rarefaction waves. A split-feature appears at the contact
discontinuity of two shells for the ``equal mass'' case, while no significant
split appears for the ``equal energy'' and ``equal rest mass density'' cases.
The shell spreading with a few ten percent of the speed of light is also shown
as a notable aspect caused by rarefaction waves. The conversion efficiency of
the bulk kinetic energy to internal one is numerically evaluated. The time
evolutions of the efficiency show deviations from the widely-used inellastic
two-point-mass-collision model.Comment: 29 pages, 16 figures, accepted by Ap
Enhanced Polarized Emission from the One-Parsec-Scale Hotspot of 3C 84 as a Result of the Interaction with Clumpy Ambient Medium
We present Very Long Baseline Array polarimetric observations of the
innermost jet of 3C84 (NGC1275) at 43GHz. A significant
polarized emission is detected at the hotspot of the innermost re-started jet,
which is located 1 pc south from the radio core. While the previous
report presented a hotspot at the southern end of the western limb, the hotspot
location has been moved to the southern end of the eastern limb. Faraday
rotation is detected within an entire bandwidth of the 43-GHz band. The
measured rotation measure (RM) is at most
(6.31.9)radm and might be slightly time
variable on the timescale of a month by a factor of a few. Our measured RM and
the RM previously reported by the CARMA and SMA observations cannot be
consistently explained by the spherical accretion flow with a power-law
profile. We propose that a clumpy/inhomogeneous ambient medium is responsible
for the observed rotation measure. Using equipartition magnetic field, we
derive the electron density of cm. Such an electron
density is consistent with the cloud of narrow line emission region around the
central engine. We also discuss the magnetic field configuration from black
hole scale to pc scale and the origin of low polarization.Comment: 8 pages, 8 figures, accepted for publication in Ap
Discovery of a wandering radio jet base after a large X-ray flare in the blazar Markarian 421
We investigate the location of the radio jet bases ("radio cores") of blazars
in radio images, and their stationarity by means of dense very long baseline
interferometry (VLBI) observations. In order to measure the position of a radio
core, we conducted 12 epoch astrometric observation of the blazar Markarian 421
with the VLBI Exploration of Radio Astrometry at 22 GHz immediately after a
large X-ray flare, which occurred in the middle of 2011 September. For the
first time, we find that the radio core is not stationary but rather changes
its location toward 0.5 mas downstream. This angular scale corresponds to the
de-projected length of a scale of Schwarzschild radii (Rs) at the
distance of Markarian~421. This radio-core wandering may be a new type of
manifestation associated with the phenomena of large X-ray flares.Comment: 6 pages, 4 figures, 1 table, has been published in ApJ Letter
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
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