938 research outputs found
Diffuse Hard X-ray Sources Discovered with the ASCA Galactic Plane Survey
We found diffuse hard X-ray sources, G11.0+0.0, G25.5+0.0, and G26.6-0.1 in
the ASCA Galactic plane survey data. The X-ray spectra are featureless with no
emission line, and are fitted with both models of a thin thermal plasma in
non-equilibrium ionization and a power-law function. The source distances are
estimated to be 1-8 kpc, using the best-fit NH values on the assumption that
the mean density in the line of sight is 1 H cm^-3. The source sizes and
luminosities are then 4.5-27 pc and (0.8-23)x10^33 ergs/s. Although the source
sizes are typical to supernova remnants (SNR) with young to intermediate ages,
the X-ray luminosity, plasma temperature, and weak emission lines in the
spectra are all unusual. This suggests that these objects are either shell-like
SNRs dominated by X-ray synchrotron emission, like SN 1006, or, alternatively,
plerionic SNRs. The total number of these classes of SNRs in our Galaxy is also
estimated.Comment: 17 pages, 9 figures; to appear in Ap
Chandra Observations of A Galactic Supernova Remnant Vela Jr.: A New Sample of Thin Filaments Emitting Synchrotron X-Rays
A galactic supernova remnant (SNR) Vela Jr. (RX J0852.04622, G266.61.2)
shows sharp filamentary structure on the north-western edge of the remnant in
the hard X-ray band. The filaments are so smooth and located on the most outer
side of the remnant. We measured the averaged scale width of the filaments
( and ) with excellent spatial resolution of {\it Chandra}, which are
in the order of the size of the point spread function of {\it Chandra} on the
upstream side and 49.5 (36.0--88.8) arcsec on the downstream side,
respectively. The spectra of the filaments are very hard and have no line-like
structure, and were well reproduced with an absorbed power-law model with
2.67 (2.55--2.77), or a {\tt SRCUT} model with = 4.3
(3.4--5.3) Hz under the assumption of . These results
imply that the hard X-rays are synchrotron radiation emitted by accelerated
electrons, as mentioned previously. Using a correlation between a function
and the SNR age, we estimated the
distance and the age of Vela Jr.: the estimated distance and age are 0.33
(0.26--0.50) kpc and 660 (420--1400) years, respectively. These results are
consistent with previous reports, implying that --age relation may be
a useful tool to estimate the distance and the age of synchrotron X-ray
emitting SNRs.Comment: 19 pages, 8 figures, ApJ, in pres
Quantum squeezing generation versus photon localization in a disordered microcavity
We investigate theoretically the nonlinear dynamics induced by an intense
pump field in a disordered planar microcavity. Through a self-consistent
theory, we show how the generation of quantum optical noise squeezing is
affected by the breaking of the in-plane translational invariance and the
occurrence of photon localization. We find that the generation of single-mode
Kerr squeezing for the ideal planar case can be prevented by disorder as a
result of multimode nonlinear coupling, even when the other modes are in the
vacuum state. However, the excess noise is a non-monotonous function of the
disorder amplitude. In the strong localization limit, we show that the system
becomes protected with respect to this fundamental coupling mechanism and that
the ideal quadrature squeezing generation can be obtained
Fine Structures of Shock of SN 1006 with the Chandra Observation
The north east shell of SN 1006 is the most probable acceleration site of
high energy electrons (up to ~ 100 TeV) with the Fermi acceleration mechanism
at the shock front. We resolved non-thermal filaments from thermal emission in
the shell with the excellent spatial resolution of Chandra. The thermal
component is extended widely over about ~ 100 arcsec (about 1 pc at 1.8 kpc
distance) in width, consistent with the shock width derived from the Sedov
solution. The spectrum is fitted with a thin thermal plasma of kT = 0.24 keV in
non-equilibrium ionization (NEI), typical for a young SNR. The non-thermal
filaments are likely thin sheets with the scale widths of ~ 4 arcsec (0.04 pc)
and ~ 20 arcsec (0.2 pc) at upstream and downstream, respectively. The spectra
of the filaments are fitted with a power-law function of index 2.1--2.3, with
no significant variation from position to position. In a standard diffusive
shock acceleration (DSA) model, the extremely small scale length in upstream
requires the magnetic field nearly perpendicular to the shock normal. The
injection efficiency (eta) from thermal to non-thermal electrons around the
shock front is estimated to be ~ 1e-3 under the assumption that the magnetic
field in upstream is 10 micro G. In the filaments, the energy densities of the
magnetic field and non-thermal electrons are similar to each other, and both
are slightly smaller than that of thermal electrons. in the same order for each
other. These results suggest that the acceleration occur in more compact region
with larger efficiency than previous studies.Comment: 24 pages, 11 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/SN1006.pd
Dissipation and detection of polaritons in ultrastrong coupling regime
We have investigated theoretically a dissipative polariton system in the
ultrastrong light-matter coupling regime without using the rotating-wave
approximation on system-reservoir coupling. Photons in a cavity and excitations
in matter respectively couple two large ensembles of harmonic oscillators
(photonic and excitonic reservoirs). Inheriting the quantum statistics of
polaritons in the ultrastrong coupling regime, in the ground state of the whole
system, the two reservoirs are not in the vacuum states but they are squeezed
and correlated. We suppose this non-vacuum reservoir state in the master
equation and in the input-output formalism with Langevin equations. Both two
approaches consistently guarantee the decay of polariton system to its ground
state, and no photon detection is also obtained when the polariton system is in
the ground state.Comment: 18 pages, 3 figure
Constraints on cosmic-ray efficiency in the supernova remnant RCW 86 using multi-wavelength observations
Several young supernova remnants (SNRs) have recently been detected in the
high-energy and very-high-energy gamma-ray domains. As exemplified by RX
J1713.7-3946, the nature of this emission has been hotly debated, and direct
evidence for the efficient acceleration of cosmic-ray protons at the SNR shocks
still remains elusive. We analyzed more than 40 months of data acquired by the
Large Area Telescope (LAT) on-board the Fermi Gamma-Ray Space Telescope in the
HE domain, and gathered all of the relevant multi-wavelength (from radio to VHE
gamma-rays) information about the broadband nonthermal emission from RCW 86.
For this purpose, we re-analyzed the archival X-ray data from the ASCA/Gas
Imaging Spectrometer (GIS), the XMM-Newton/EPIC-MOS, and the RXTE/Proportional
Counter Array (PCA). Beyond the expected Galactic diffuse background, no
significant gamma-ray emission in the direction of RCW 86 is detected in any of
the 0.1-1, 1-10 and 10-100 GeV Fermi-LAT maps. In the hadronic scenario, the
derived HE upper limits together with the HESS measurements in the VHE domain
can only be accommodated by a spectral index Gamma <= 1.8, i.e. a value
in-between the standard (test-particle) index and the asymptotic limit of
theoretical particle spectra in the case of strongly modified shocks. The
interpretation of the gamma-ray emission by inverse Compton scattering of high
energy electrons reproduces the multi-wavelength data using a reasonable value
for the average magnetic field of 15-25 muG. For these two scenarios, we
assessed the level of acceleration efficiency. We discuss these results in the
light of existing estimates of the magnetic field strength, the effective
density and the acceleration efficiency in RCW 86.Comment: Accepted for publication in A&A; 10 pages and 4 figure
Thermal and Non-thermal X-Rays from the LMC Super Bubble 30 Dor C
We report on the discovery of thermal and non-thermal X-rays from the shells
of the super bubble (SB) 30 Dor C in the Large Magellanic Cloud (LMC). The
X-ray morphology is a nearly circular shell with a radius of about 40 pc, which
is bright on the northern and western sides. The spectra of the shells are
different from region to region. The southern shell shows clear emission lines,
and is well fitted with a model of a thin-thermal plasma (kT = 0.21keV) in
non-equilibrium ionization (NEI) plus a power-law component. This thermal
plasma is located inside of the H alpha emission, which is the outer edge of
the shell of the SB. The northern and western sides of the SB are dim in H
alpha emission, but are bright in non-thermal (power-law) X-rays with a photon
index of 2.1-2.9. The non-thermal X-ray shell traces the outer boundary of the
radio shell. These features of thin-thermal and non-thermal X-rays are similar
to those of SN 1006, a prototype of synchrotron X-ray shell, but the
non-thermal component of 30 Dor C is about ten-times brighter than that of SN
1006. 30 Dor C is the first candidate of an extragalactic SB, in which
energetic electrons are accelerating in the shell. The age is much older than
that of SN 1006, and hence the particle acceleration time in this SB may be
longer than those in normal shell-like SNRs. We found point-like sources
associated with some of tight star clusters. The X-ray luminosity and spectrum
are consistent with those of young clusters of massive stars. Point-like
sources with non-thermal spectra are also found in the SB. These may be
background objects (AGNs) or stellar remnants (neutron stars or black holes).Comment: 11 pages, 6 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/30DorC.pd
X-Ray Synchrotron Emitting Fe-Rich Ejecta in SNR RCW 86
Supernova remnants may exhibit both thermal and nonthermal X-ray emission. We
present Chandra observations of RCW 86. Striking differences in the morphology
of X-rays below 1 keV and above 2 keV point to a different physical origin.
Hard X-ray emission is correlated fairly well with the edges of regions of
radio emission, suggesting that these are the locations of shock waves at which
both short-lived X-ray emitting electrons, and longer-lived radio-emitting
electrons, are accelerated. Soft X-rays are spatially well-correlated with
optical emission from nonradiative shocks, which are almost certainly portions
of the outer blast wave. These soft X-rays are well fit with simple thermal
plane-shock models. Harder X-rays show Fe K alpha emission and are well
described with a similar soft thermal component, but a much stronger
synchrotron continuum dominating above 2 keV, and a strong Fe K alpha line.
Quantitative analysis of this line and the surrounding continuum shows that it
cannot be produced by thermal emission from a cosmic-abundance plasma; the
ionization time is too short, as shown both by the low centroid energy (6.4
keV) and the absence of oxygen lines below 1 keV. Instead, a model of a plane
shock into Fe-rich ejecta, with a synchrotron continuum, provides a natural
explanation. This requires that reverse shocks into ejecta be accelerating
electrons to energies of order 50 TeV. We show that maximum energies of this
order can be produced by radiation-limited diffusive shock acceleration at the
reverse shocks.Comment: ApJ, accepted; full resolution images in
http://spider.ipac.caltech.edu/staff/rho/rcw86chandra.p
Gravity and Electromagnetism with -type Coupling and Magnetic Monopole Solutions
We investigate -type coupling of electromagnetic fields to
gravity. After we derive field equations by a first order variational principle
from the Lagrangian formulation of the non-minimally coupled theory, we look
for static, spherically symmetric, magnetic monopole solutions. We point out
that the solutions can provide possible geometries which may explain the
flatness of the observed rotation curves of galaxies.Comment: 10 page
A Spatial and Spectral Study of Nonthermal Filaments in Historical Supernova Remnants: Observational Results with Chandra
The outer shells of young supernova remnants (SNRs) are the most plausible
acceleration sites of high-energy electrons with the diffusive shock
acceleration (DSA) mechanism. We studied spatial and spectral properties close
to the shock fronts in four historical SNRs (Cas A, Kepler's remnant, Tycho's
remnant, and RCW 86) with excellent spatial resolution of {\it Chandra}. In all
of the SNRs, hard X-ray emissions were found on the rims of the SNRs, which
concentrate in very narrow regions (so-called "filaments"); apparent scale
widths on the upstream side are below or in the order of the point spread
function of {\it Chandra}, while 0.5--40 arcsec (0.01--0.4 pc) on the
downstream side with most reliable distances. The spectra of these filaments
can be fitted with both thermal and nonthermal (power-law and {\tt SRCUT})
models. The former requires unrealistic high temperature (\ga2 keV) and low
abundances (\la1 solar) for emission from young SNRs and may be thus
unlikely. The latter reproduces the spectra with best-fit photon indices of
2.1--3.8, or roll-off frequencies of (0.1--28) Hz, which
reminds us of the synchrotron emission from electrons accelerated via DSA. We
consider various physical parameters as functions of the SNR age, including the
previous results on SN 1006 \citep{bamba2003b}; the filament width on the
downstream side increases with the SNR age, and the spectrum becomes softer
keeping a nonthermal feature. It was also found that a function, that is the
roll-off frequency divided by the square of the scale width on the downstream
side, shows negative correlation with the age, which might provide us some
information on the DSA theory.Comment: 23 pages, 23 figures, accepted by Ap
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