1,454 research outputs found
Obscuring Material around Seyfert Nuclei with Starbursts
The structure of obscuring matter in the environment of active galactic
nuclei with associated nuclear starbursts is investigated using 3-D
hydrodynamical simulations. Simple analytical estimates suggest that the
obscuring matter with energy feedback from supernovae has a torus-like
structure with a radius of several tens of parsecs and a scale height of about
10 pc. These estimates are confirmed by the fully non-linear numerical
simulations, in which the multi-phase inhomogeneous interstellar matter and its
interaction with the supernovae are consistently followed. The globally stable,
torus-like structure is highly inhomogeneous and turbulent. To achieve the high
column densities (> 10^{24} cm^{-2}) as suggested by observations of some
Seyfert 2 galaxies with nuclear starbursts, the viewing angle should be larger
than about 70 degree from the pole-on for a 10^8 solar mass massive black hole.
Due to the inhomogeneous internal structure of the torus, the observed column
density is sensitive to the line-of-sight, and it fluctuates by a factor of
order 100. The covering fraction for N > 10^{23} cm^{-2} is about 0.4. The
average accretion rate toward R < 1 pc is 0.4 solar mass/yr, which is boosted
to twice that in the model without the energy feedback.Comment: ApJL in press (4 pages, 3 figures) A gziped ps file with high
resolution figures is available at http://th.nao.ac.jp/~wada/AGN
Quantum diffraction and interference of spatially correlated photon pairs and its Fourier-optical analysis
We present one- and two-photon diffraction and interference experiments
involving parametric down-converted photon pairs. By controlling the divergence
of the pump beam in parametric down-conversion, the diffraction-interference
pattern produced by an object changes from a quantum (perfectly correlated)
case to a classical (uncorrelated) one. The observed diffraction and
interference patterns are accurately reproduced by Fourier-optical analysis
taking into account the quantum spatial correlation. We show that the relation
between the spatial correlation and the object size plays a crucial role in the
formation of both one- and two-photon diffraction-interference patterns.Comment: 10 pages, 13 figures, rev.
The Global Structure and Evolution of a Self-Gravitating Multi-phase Interstellar Medium in a Galactic Disk
Using high resolution, two-dimensional hydrodynamical simulations, we
investigate the evolution of a self-gravitating multi-phase interstellar medium
in the central kiloparsec region of a galactic disk. We find that a
gravitationally and thermally unstable disk evolves, in a self-stabilizing
manner, into a globally quasi-stable disk that consists of cold (T < 100 K),
dense clumps and filaments surrounded by hot (T > 10^4 K), diffuse medium. The
quasi-stationary, filamentary structure of the cold gas is remarkable. The hot
gas, characterized by low-density holes and voids, is produced by shock
heating. The shocks derive their energy from differential rotation and
gravitational perturbations due to the formation of cold dense clumps. In the
quasi-stable phase where cold and dense clouds are formed, the effective
stability parameter, Q, has a value in the range 2-5. The dynamic range of our
multi-phase calculations is 10^6 - 10^7 in both density and temperature. Phase
diagrams for this turbulent medium are analyzed and discussed.Comment: 10 pages, 3 figures, ApJ Letters in press (vol. 516
Four-Photon Quantum Interferometry at a Telecom Wavelength
We report the experimental demonstration of four-photon quantum interference
using telecom-wavelength photons. Realization of multi-photon quantum
interference is essential to linear optics quantum information processing and
measurement-based quantum computing. We have developed a source that
efficiently emits photon pairs in a pure spectrotemporal mode at a telecom
wavelength region, and have demonstrated the quantum interference exhibiting
the reduced fringe intervals that correspond to the reduced de Broglie
wavelength of up to the four photon `NOON' state. Our result should open a path
to practical quantum information processing using telecom-wavelength photons.Comment: 4 pages, 4 figure
3D Models for High Velocity Features in Type Ia Supernovae
Spectral synthesis in 3-dimensional (3D) space for the earliest spectra of
Type Ia supernovae (SNe Ia) is presented. In particular, the high velocity
absorption features that are commonly seen at the earliest epochs (
days before maximum light) are investigated by means of a 3D Monte Carlo
spectral synthesis code. The increasing number of early spectra available
allows statistical study of the geometry of the ejecta. The observed diversity
in strength of the high velocity features (HVFs) can be explained in terms of a
``covering factor'', which represents the fraction of the projected photosphere
that is concealed by high velocity material. Various geometrical models
involving high velocity material with a clumpy structure or a thick torus can
naturally account for the observed statistics of HVFs. HVFs may be formed by a
combination of density and abundance enhancements. Such enhancements may be
produced in the explosion itself or may be the result of interaction with
circumstellar material or an accretion disk. Models with 1 or 2 blobs, as well
as a thin torus or disk-like enhancement are unlikely as a standard situation.Comment: 17 pages, 12 figures. Accepted for publication in the Astrophysical
Journa
Three Dimensional Simulation of Gamma Ray Emission from Asymmetric Supernovae and Hypernovae
Hard X- and -ray spectra and light curves resulting from radioactive
decays are computed for aspherical (jet-like) and energetic supernova models
(representing a prototypical hypernova SN 1998bw), using a 3D energy- and
time-dependent Monte Carlo scheme. The emission is characterized by (1) early
emergence of high energy emission, (2) large line-to-continuum ratio, and (3)
large cut-off energy by photoelectric absorptions in hard X-ray energies. These
three properties are not sensitively dependent on the observer's direction. On
the other hand, fluxes and line profiles depend sensitively on the observer's
direction, showing larger luminosity and larger degree of blueshift for an
observer closer to the polar () direction. Strategies to derive the degree
of asphericity and the observer's direction from (future) observations are
suggested on the basis of these features, and an estimate on detectability of
the high energy emission by the {\it INTEGRAL} and future observatories is
presented. Also presented is examination on applicability of a gray effective
-ray opacity for computing the energy deposition rate in the aspherical
SN ejecta. The 3D detailed computations show that the effective -ray
opacity cm g reproduces the
detailed energy-dependent transport for both spherical and aspherical
(jet-like) geometry.Comment: 24 pages, 13 figures. Figure 7 added in the accepted version. ApJ,
644 (01 June 2006 issue), in press. Resolution of figures lower than the
published versio
The Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars: Black Hole-forming Supernovae with Relativistic Jets
Long-duration gamma-ray bursts (GRBs) are thought to be connected to luminous
and energetic supernovae (SNe), called hypernovae (HNe), resulting from the
black-hole (BH) forming collapse of massive stars. For recent nearby
GRBs~060505 and 060614, however, the expected SNe have not been detected. The
upper limits to the SN brightness are about 100 times fainter than
GRB-associated HNe (GRB-HNe), corresponding to the upper limits to the ejected
Ni masses of . SNe with a small
amount of Ni ejection are observed as faint Type II SNe. HNe and faint
SNe are thought to be responsible for the formation of extremely metal-poor
(EMP) stars. In this Letter, a relativistic jet-induced BH forming explosion of
the 40 star is investigated and hydrodynamic and nucleosynthetic
models are presented. These models can explain both GRB-HNe and GRBs without
bright SNe in a unified manner. Their connection to EMP stars is also
discussed. We suggest that GRBs without bright SNe are likely to synthesize
\Mni\sim 10^{-4} to or .Comment: 7 pages, 3 figures. Accepted for publication in the Astrophysical
Journal Letters (10 March 2007, v657n2 issue
Multi-Dimensional Simulations for Early Phase Spectra of Aspherical Hypernovae: SN 1998bw and Off-Axis Hypernovae
Early phase optical spectra of aspherical jet-like supernovae (SNe) are
presented. We focus on energetic core-collapse SNe, or hypernovae. Based on
hydrodynamic and nucleosynthetic models, radiative transfer in SN atmosphere is
solved with a multi-dimensional Monte-Carlo radiative transfer code, SAMURAI.
Since the luminosity is boosted in the jet direction, the temperature there is
higher than in the equatorial plane by ~ 2,000 K. This causes anisotropic
ionization in the ejecta. Emergent spectra are different depending on viewing
angle, reflecting both aspherical abundance distribution and anisotropic
ionization. Spectra computed with an aspherical explosion model with kinetic
energy 20 x 10^{51} ergs are compatible with those of the Type Ic SN 1998bw if
~ 10-20% of the synthesized metals are mixed out to higher velocities. The
simulations enable us to predict the properties of off-axis hypernovae. Even if
an aspherical hypernova explosion is observed from the side, it should show
hypernova-like spectra but with some differences in the line velocity, the
width of the Fe absorptions and the strength of the Na I line.Comment: 4 pages, 4 figures. Accepted for publication in The Astrophysical
Journal Letter
The evolution of the peculiar Type Ia supernova SN 2005hk over 400 days
photometry and medium resolution optical spectroscopy of peculiar
Type Ia supernova SN 2005hk are presented and analysed, covering the
pre-maximum phase to around 400 days after explosion. The supernova is found to
be underluminous compared to "normal" Type Ia supernovae. The photometric and
spectroscopic evolution of SN 2005hk is remarkably similar to the peculiar Type
Ia event SN 2002cx. The expansion velocity of the supernova ejecta is found to
be lower than normal Type Ia events. The spectra obtained \gsim 200 days
since explosion do not show the presence of forbidden [\ion{Fe}{ii}],
[\ion{Fe}{iii}] and [\ion{Co}{iii}] lines, but are dominated by narrow,
permitted \ion{Fe}{ii}, NIR \ion{Ca}{ii} and \ion{Na}{i} lines with P-Cygni
profiles. Thermonuclear explosion model with Chandrasekhar mass ejecta and a
kinetic energy smaller (\KE = 0.3 \times 10^{51} {\rm ergs}) than that of
canonical Type Ia supernovae is found to well explain the observed bolometric
light curve. The mass of \Nifs synthesized in this explosion is 0.18 \Msun.
The early spectra are successfully modeled with this less energetic model with
some modifications of the abundance distribution. The late spectrum is
explained as a combination of a photospheric component and a nebular component.Comment: Accepted for publication in The Astrophysical Journal. Minor
revision, discussion section adde
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