19,923 research outputs found
X-ray and Radio Follow-up Observations of High-Redshift Blazar Candidates in the Fermi-LAT Unassociated Source Population
We report on the results of X-ray and radio follow-up observations of two GeV
gamma-ray sources 2FGL J0923.5+1508 and 2FGL J1502.1+5548, selected as
candidates for high-redshift blazars from unassociated sources in the {\it
Fermi} Large Area Telescope Second Source Catalog. We utilize the Suzaku
satellite and the VLBI Exploration of Radio Astrometry (VERA) telescopes for
X-ray and radio observations, respectively. For 2FGL J0923.5+1508, a possible
radio counterpart NVSS J092357+150518 is found at 1.4 GHz from an existing
catalog, but we do not detect any X-ray emission from it and derive a flux
upper limit 1.37 10 erg cm
s. Radio observations at 6.7 GHz also result in an upper limit of
19 mJy, implying a steep radio spectrum that is not
expected for a blazar. On the other hand, we detect X-rays from NVSS
J150229+555204, the potential 1.4 GHz radio counterpart of 2FGL J1502.1+5548.
The X-ray spectrum can be fitted with an absorbed power-law model with a photon
index =1.8 and the unabsorbed flux is =4.3 10 erg cm s. Moreover,
we detect unresolved radio emission at 6.7 GHz with flux =30.1
mJy, indicating a compact, flat-spectrum radio source. If NVSS J150229+555204
is indeed associated with 2FGL J1502.1+5548, we find that its multiwavelength
spectrum is consistent with a blazar at redshift .Comment: 24 pages, 7 figures, 6 tables, accepted for publication in Ap
Giant Intrinsic Spin and Orbital Hall Effects in Sr2MO4 (M=Ru,Rh,Mo)
We investigate the intrinsic spin Hall conductivity (SHC) and the d-orbital
Hall conductivity (OHC) in metallic d-electron systems, by focusing on the
t_{2g}-orbital tight-binding model for Sr2MO4 (M=Ru,Rh,Mo). The conductivities
obtained are one or two orders of magnitude larger than predicted values for
p-type semiconductors with 5% hole doping. The origin of these giant Hall
effects is the ``effective Aharonov-Bohm phase'' that is induced by the
d-atomic angular momentum in connection with the spin-orbit interaction and the
inter-orbital hopping integrals. The huge SHC and OHC generated by this
mechanism are expected to be ubiquitous in multiorbital transition metal
complexes, which pens the possibility of realizing spintronics as well as
orbitronics devices.Comment: 5 pages, accepted for publication in PR
Flat-band excitonic states in Kagome lattice on semiconductor surface
Excitonic properties in the Kagome lattice system, which is produced by
quantum wires on semiconductor surfaces, are investigated by using the exact
diagonalization of a tight binding model. It is shown that due to the existence
of flat bands the binding energy of exciton becomes remarkably large in the
two-dimensional Kagome lattice compared to that in one-dimensional lattice, and
the exciton Bohr radius is quite small as large as a lattice constant. We also
discuss the magnetic field effects on the exciton binding energy and the
stability of exciton against the creation of charged exciton and biexciton.Comment: 5 pages, 5 figure
How large is our universe?
We reexamine constraints on the spatial size of closed toroidal models with
cold dark matter and the cosmological constant from cosmic microwave
background. We carry out Bayesian analyses using the Cosmic Background Explorer
(COBE) data properly taking into account the statistically anisotropic
correlation, i.e., off-diagonal elements in the covariance. We find that the
COBE constraint becomes more stringent in comparison with that using only the
angular power spectrum, if the likelihood is marginalized over the orientation
of the observer. For some limited choices of orientations, the fit to the COBE
data is considerably better than that of the infinite counterpart. The best-fit
matter normalization is increased because of large-angle suppression in the
power and the global anisotropy of the temperature fluctuations. We also study
several deformed closed toroidal models in which the fundamental cell is
described by a rectangular box. In contrast to the cubic models, the
large-angle power can be enhanced in comparison with the infinite counterparts
if the cell is sufficiently squashed in a certain direction. It turns out that
constraints on some slightly deformed models are less stringent. We comment on
how these results affect our understanding of the global topology of our
universe.Comment: 19 pages, 9 figures, version accepted for PRD. More elaborate
discussion on the best-fit orientation has been adde
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