460 research outputs found
Balmer Line Variations in the Radio-Loud AGN PG 1512+370
We present spectroscopic observations of the quasar PG~1512+370, covering the
Hbeta line spectral range and collected at moderate resolution (2-7 A FWHM)
from 1988 to 1996. The observations show that the blue wing of the Hbeta broad
profile component has changed significantly in flux and shape between 1988 and
1990 and between 1995 and 1996. A displaced blue peak on the Hbeta profile,
visible in 1988, but not in the 1990-1995 spectra, is revealed again in one of
the spectra obtained in 1996. The blue peak (in both the 1988 and 1996 spectra)
is centered at Delta v_r ~ -3000 +/- 500 km/s from the rest frame defined by
the narrow component of Hbeta, and the OIII lambda4959,5007 lines.
We discuss several conflicting interpretations of the data. We find that the
variability of the Hbeta blue wing is consistent with Balmer line emission from
regions whose motion is predominantly radial, if variations of the blue wing
are a response to continuum changes. Alternatively, we note that observed Hbeta
line profile variations are consistent with a variable line component as in a
``binary black hole'' scenario. More frequent observations of Hbeta are needed
to distinguish among these hypotheses.Comment: 19 pages, 1 embedded figure (eps), to appear in ApJ 49
Proximity effect-assisted absorption of spin currents in superconductors
The injection of pure spin current into superconductors by the dynamics of a
ferromagnetic contact is studied theoretically. Taking into account suppression
of the order parameter at the interfaces (inverse proximity effect) and the
energy-dependence of spin-flip scattering, we determine the
temperature-dependent ferromagnetic resonance linewidth broadening. Our results
agree with recent experiments in Nb|permalloy bilayers [C. Bell et al.,
arXiv:cond-mat/0702461].Comment: 4 page
Observation of Berry's Phase in a Solid State Qubit
In quantum information science, the phase of a wavefunction plays an
important role in encoding information. While most experiments in this field
rely on dynamic effects to manipulate this information, an alternative approach
is to use geometric phase, which has been argued to have potential fault
tolerance. We demonstrate the controlled accumulation of a geometric phase,
Berry's phase, in a superconducting qubit, manipulating the qubit geometrically
using microwave radiation, and observing the accumulated phase in an
interference experiment. We find excellent agreement with Berry's predictions,
and also observe a geometry dependent contribution to dephasing.Comment: 5 pages, 4 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Tunable resonators for quantum circuits
We have designed, fabricated and measured high-Q coplanar
waveguide microwave resonators whose resonance frequency is made tunable with
magnetic field by inserting a DC-SQUID array (including 1 or 7 SQUIDs) inside.
Their tunability range is 30% of the zero field frequency. Their quality factor
reaches up to 3. We present a model based on thermal fluctuations
that accounts for the dependance of the quality factor with magnetic field.Comment: subm. to JLTP (Proc. of LTD12 conference
Optomechanical zipper cavity lasers: theoretical analysis of tuning range and stability
The design of highly wavelength tunable semiconductor laser structures is
presented. The system is based on a one dimensional photonic crystal cavity
consisting of two patterned, doubly-clamped nanobeams, otherwise known as a
"zipper" cavity. Zipper cavities are highly dispersive with respect to the gap
between nanobeams in which extremely strong radiation pressure forces exist.
Schemes for controlling the zipper cavity wavelength both optically and
electrically are presented. Tuning ranges as high as 75nm are achieved for a
nominal design wavelength of 1.3micron. Sensitivity of the mechanically
compliant laser structure to thermal noise is considered, and it is found that
dynamic back-action of radiation pressure in the form of an optical or
electrical spring can be used to stabilize the laser frequency. Fabrication of
zipper cavity laser structures in GaAs material with embedded self-assembled
InAs quantum dots is presented, along with measurements of photoluminescence
spectroscopy of the zipper cavity modes.Comment: 20 pages, 8 figure
Broadband Spectral Analysis of PKS 0528+134: A Report on Six Years of EGRET Observations
The multiwavelength spectra of PKS 0528+134 during six years of observations
by EGRET have been analyzed using synchrotron self-Compton (SSC) and external
radiation Compton (ERC) models. We find that a two-component model, in which
the target photons are produced externally to the gamma-ray emitting region,
but also including an SSC component, is required to suitably reproduce the
spectral energy distributions of the source. Our analysis indicates that there
is a trend in the observed properties of PKS 0528+134, as the source goes from
a gamma-ray low state to a flaring state. We observe that during the higher
gamma-ray states, the bulk Lorentz factor of the jet increases and the ERC
component dominates the high-energy emission. Our model calculations indicate
the trend that the energies of the electrons giving rise to the synchrotron
peak decreases, and the power-ratio of the gamma-ray and low energy spectral
components increases, as the source goes from a low to a high gamma-ray state.Comment: 36 pages, 13 figures, final version accepted for publication in ApJ;
includes minor modification
The 72-Hour WEBT Microvariability Observation of Blazar S5 0716+714 in 2009
Context. The international whole earth blazar telescope (WEBT) consortium
planned and carried out three days of intensive micro-variability observations
of S5 0716+714 from February 22, 2009 to February 25, 2009. This object was
chosen due to its bright apparent magnitude range, its high declination, and
its very large duty cycle for micro-variations. Aims. We report here on the
long continuous optical micro-variability light curve of 0716+714 obtained
during the multi-site observing campaign during which the Blazar showed almost
constant variability over a 0.5 magnitude range. The resulting light curve is
presented here for the first time. Observations from participating
observatories were corrected for instrumental differences and combined to
construct the overall smoothed light curve. Methods. Thirty-six observatories
in sixteen countries participated in this continuous monitoring program and
twenty of them submitted data for compilation into a continuous light curve.
The light curve was analyzed using several techniques including Fourier
transform, Wavelet and noise analysis techniques. Those results led us to model
the light curve by attributing the variations to a series of synchrotron
pulses. Results. We have interpreted the observed microvariations in this
extended light curve in terms of a new model consisting of individual
stochastic pulses due to cells in a turbulent jet which are energized by a
passing shock and cool by means of synchrotron emission. We obtained an
excellent fit to the 72-hour light curve with the synchrotron pulse model
TEMPO2, a new pulsar timing package. III: Gravitational wave simulation
Analysis of pulsar timing data-sets may provide the first direct detection of
gravitational waves. This paper, the third in a series describing the
mathematical framework implemented into the tempo2 pulsar timing package,
reports on using tempo2 to simulate the timing residuals induced by
gravitational waves. The tempo2 simulations can be used to provide upper bounds
on the amplitude of an isotropic, stochastic, gravitational wave background in
our Galaxy and to determine the sensitivity of a given pulsar timing experiment
to individual, supermassive, binary black hole systems.Comment: Accepted by MNRA
The Sensitivity of the Parkes Pulsar Timing Array to Individual Sources of Gravitational Waves
We present the sensitivity of the Parkes Pulsar Timing Array to gravitational
waves emitted by individual super-massive black-hole binary systems in the
early phases of coalescing at the cores of merged galaxies. Our analysis
includes a detailed study of the effects of fitting a pulsar timing model to
non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies
and hence complementary to LIGO and LISA. We place a sky-averaged constraint on
the merger rate of nearby () black-hole binaries in the early phases
of coalescence with a chirp mass of 10^{10}\,\rmn{M}_\odot of less than one
merger every seven years. The prospects for future gravitational-wave astronomy
of this type with the proposed Square Kilometre Array telescope are discussed.Comment: fixed error in equation (4). [13 pages, 6 figures, 1 table, published
in MNRAS
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