6,316 research outputs found
A Deep Optical Observation for an Enigmatic Unidentified Gamma-Ray Source 3EG J1835+5918
We report a deep optical imaging observation by the Subaru telescope for a
very soft X-ray source RX J1836.2+5925, which has been suspected to be an
isolated neutron star associated with the brightest as-yet unidentified EGRET
source outside the Galactic plane, 3EG J1835+5918. An extended source having a
complex, bipolar shape is found at B ~ 26, and this might be an extended pulsar
nebular whose flux is about 5-6 orders of magnitude lower than gamma-ray flux,
although finding a galaxy of this magnitude by chance in the error circle is of
order unity. We have found two even fainter, possibly point sources at B ~ 28,
although their detections are not firm because of low signal-to-noise. If the
extended object of B ~ 26 is a galaxy and not related to 3EG J1835+5918, a
lower limit on X-ray/optical flux ratio is set as f_X/f_B >~ 2700, giving a
further strong support of the neutron-star identification of 3EG J1835+5918.
Interestingly, if either of the two sources at B ~ 28 is the real counterpart
of RX J1836.2+5925 and thermal emission from the surface of an isolated neutron
star, the temperature and distance to the source become ~ 4 x 10^5K and ~300pc,
respectively, showing a striking similarity of its spectral energy distribution
to the proto-type radio-quiet gamma-ray pulsar Geminga. No detection of
nonthermal hard X-ray emission is consistent with the ASCA upper limit, if the
nonthermal flux of 3EG J1835+5918/RX J1836.2+5925 is at a similar level with
that of Gemiga.Comment: PASJ Letters in press. (Received March 26; Accepted May 17
Positional Coincidence between the High-latitude Steady Unidentified Gamma-ray Sources and Possibly Merging Clusters of Galaxies
We report an evidence for the first time that merging clusters of galaxies
are a promising candidate for the origin of high galactic-latitude, steady
unidentified EGRET gamma-ray sources. Instead of using past optical catalogs of
eye-selected clusters, we made a matched-filter survey of galaxy clusters over
4\arcdeg \times 4\arcdeg areas around seven steady unidentified EGRET sources
at |b|>45\arcdeg together with a 100 \sq \arcdeg area near the South
Galactic Pole as a control field. In total, 154 Abell-like cluster candidates
and 18 close pairs/groups of these clusters, expected to be possibly merging
clusters, were identified within estimated redshift . Five
among the seven EGRET sources have one or two cluster pairs/groups (CPGs)
within 1\arcdeg from them. We assess the statistical significance of this
result by several methods, and the confidence level of the real excess is
maximally 99.8% and 97.8% in a conservative method. In contrast, we found no
significant correlation with single clusters. In addition to the spatial
correlation, we also found that the richness of CPGs associated with EGRET
sources is considerably larger than those of CPGs in the control field. These
results imply that a part of the steady unidentified EGRET sources at
high-latitude are physically associated with close CPGs, not with single
clusters. We also discuss possible interpretations of these results. We argue
that, if these associations are real, they are difficult to explain by hadronic
processes, but best explained by the inverse-Compton scattering by high energy
electrons accelerated in shocks of cluster formation, as recently proposed.Comment: 9 pages, 2 PostScript figures, uses emulateapj5.sty, added new
analysis and discussion, ApJ accepte
Solving Cosmological Problems of Supersymmetric Axion Models in an Inflationary Universe
We revisit inflationary cosmology of axion models in the light of recent
developments on the inflaton decay in supergravity. We find that all the
cosmological difficulties, including gravitino, axino overproduction and
axionic isocurvature fluctuation, can be avoided if the saxion field has large
initial amplitude during inflation and decays before big-bang nucleosynthesis.Comment: 19 pages, 4 figure
Non-equilibrium critical behavior : An extended irreversible thermodynamics approach
Critical phenomena in non-equilibrium systems have been studied by means of a
wide variety of theoretical and experimental approaches. Mode-coupling,
renormalization group, complex Lie algebras and diagrammatic techniques are
some of the usual theoretical tools. Experimental studies include light and
inelastic neutron scattering, X-ray photon correlation spectroscopy, microwave
interferometry and several other techniques. Nevertheless no conclusive
reatment has been developed from the basic principles of a thermodynamic theory
of irreversible processes. We have developed a formalism in which we obtain
correlation functions as field averages of the associated functions. By
applying such formalism we attempt to find out if the resulting correlation
functions will inherit the mathematical properties (integrability, generalized
homogeneity, scaling laws) of its parent potentials, and we will also use these
correlation functions to study the behavior of macroscopic systems far from
equilibrium, specially in the neighborhood of critical points or dynamic phase
transitions. As a working example we will consider the mono-critical behavior
of a non-equilibrium binary fluid mixture close to its consolute point.Comment: 23 pages, 3 figures, 1 tabl
Mode coupling theory in the FDR-preserving field theory of interacting Brownian particles
We develop a renormalized perturbation theory for the dynamics of interacting
Brownian particles, which preserves the fluctuation-dissipation relation order
by order. We then show that the resulting one-loop theory gives a closed
equation for the density correlation function, which is identical with that in
the standard mode coupling theory.Comment: version to be published in Fast Track Communication in Journal of
Physics A:Math. Theo
Hysteretic current-voltage characteristics and resistance switching at an epitaxial oxide Schottky junction SrRuO/SrTiNbO
Transport properties have been studied for a perovskite heterojunction
consisting of SrRuO (SRO) film epitaxially grown on
SrTiNbO (Nb:STO) substrate. The SRO/Nb:STO interface
exhibits rectifying current-voltage (-) characteristics agreeing with
those of a Schottky junction composed of a deep work-function metal (SRO) and
an -type semiconductor (Nb:STO). A hysteresis appears in the -
characteristics, where high resistance and low resistance states are induced by
reverse and forward bias stresses, respectively. The resistance switching is
also triggered by applying short voltage pulses of 1 s - 10 ms duration.Comment: 3 pages, 3 figures, Appl. Phys. Lett., in pres
Cosmological Constraints on Late-time Entropy Production
We investigate cosmological effects concerning the late-time entropy
production due to the decay of non-relativistic massive particles. The
thermalization process of neutrinos after the entropy production is properly
solved by using the Boltzmann equation. If a large entropy production takes
place at late time t 1 sec, it is found that a large fraction of
neutrinos cannot be thermalized. This fact loosens the tight constraint on the
reheating temperature T_R from the big bang nucleosynthesis and T_R could be as
low as 0.5 MeV. The influence on the large scale structure formation and cosmic
microwave background anisotropies is also discussed.Comment: 4 pages, using RevTeX and five postscript figures, comments added, to
appear in Phys. Rev. Let
New Superconducting and Magnetic Phases Emerge on the Verge of Antiferromagnetism in CeIn
We report the discovery of new superconducting and novel magnetic phases in
CeIn on the verge of antiferromagnetism (AFM) under pressure () through
the In-nuclear quadrupole resonance (NQR) measurements. We have found a
-induced phase separation of AFM and paramagnetism (PM) without any trace
for a quantum phase transition in CeIn. A new type of superconductivity
(SC) was found in GPa to coexist with AFM that is magnetically
separated from PM where the heavy fermion SC takes place. We propose that the
magnetic excitations such as spin-density fluctuations induced by the
first-order magnetic phase transition might mediate attractive interaction to
form Cooper pairs.Comment: 4 pages, 4 EPS figures, submitted to J. Phys. Soc. Jp
Non-destructive imaging of an individual protein
The mode of action of proteins is to a large extent given by their ability to
adopt different conformations. This is why imaging single biomolecules at
atomic resolution is one of the ultimate goals of biophysics and structural
biology. The existing protein database has emerged from X-ray crystallography,
NMR or cryo-TEM investigations. However, these tools all require averaging over
a large number of proteins and thus over different conformations. This of
course results in the loss of structural information. Likewise it has been
shown that even the emergent X-FEL technique will not get away without
averaging over a large quantity of molecules. Here we report the first
recordings of a protein at sub-nanometer resolution obtained from one
individual ferritin by means of low-energy electron holography. One single
protein could be imaged for an extended period of time without any sign of
radiation damage. Since ferritin exhibits an iron core, the holographic
reconstructions could also be cross-validated against TEM images of the very
same molecule by imaging the iron cluster inside the molecule while the protein
shell is decomposed
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