4,362 research outputs found
Statistics of Cosmological Black Hole Jet Sources: Blazar Predictions for GLAST
A study of the statistics of cosmological black-hole jet sources is applied
to EGRET blazar data, and predictions are made for GLAST. Black-hole jet
sources are modeled as collimated relativistic plasma outflows with radiation
beamed along the jet axis due to strong Doppler boosting. The comoving rate
density of blazar flares is assumed to follow a blazar formation rate (BFR),
modeled by analytic functions based on astronomical observations and fits to
EGRET data. The redshift and size distributions of gamma-ray blazars observed
with EGRET, separated into BL Lac object (BL) and flat spectrum radio quasar
(FSRQ) distributions, are fit with monoparametric functions for the
distributions of the jet Lorentz factor \Gamma, comoving directional power
l'_e, and spectral slope. A BFR factor ~10 x greater at z ~ 1 than at present
is found to fit the FSRQ data. A smaller comoving rate density and greater
luminosity of BL flares at early times compared to the present epoch fits the
BL data. Based on the EGRET observations, ~1000 blazars consisting of ~800
FSRQs and FR2 radio galaxies and ~200 BL Lacs and FR1 radio galaxies will be
detected with GLAST during the first year of the mission. Additional AGN
classes, such as hard-spectrum BL Lacs that were mostly missed with EGRET,
could add more GLAST sources. The FSRQ and BL contributions to the EGRET
gamma-ray background at 1 GeV are estimated at the level of ~10 - 15% and ~2 -
4%, respectively. EGRET and GLAST sensitivities to blazar flares are considered
in the optimal case, and a GLAST analysis method for blazar detection is
outlined.Comment: 17 pages, 9 figures, ApJ, in press, v.660, May 1, 2007 (minor changes
from previous version
Adiabatic Quantum State Manipulation of Single Trapped Atoms
We use microwave induced adiabatic passages for selective spin flips within a
string of optically trapped individual neutral Cs atoms. We
position-dependently shift the atomic transition frequency with a magnetic
field gradient. To flip the spin of a selected atom, we optically measure its
position and sweep the microwave frequency across its respective resonance
frequency. We analyze the addressing resolution and the experimental robustness
of this scheme. Furthermore, we show that adiabatic spin flips can also be
induced with a fixed microwave frequency by deterministically transporting the
atoms across the position of resonance.Comment: 4 pages, 4 figure
Coherence properties and quantum state transportation in an optical conveyor belt
We have prepared and detected quantum coherences with long dephasing times at
the level of single trapped cesium atoms. Controlled transport by an "optical
conveyor belt" over macroscopic distances preserves the atomic coherence with
slight reduction of coherence time. The limiting dephasing effects are
experimentally identified and are of technical rather than fundamental nature.
We present an analytical model of the reversible and irreversible dephasing
mechanisms. Coherent quantum bit operations along with quantum state transport
open the route towards a "quantum shift register" of individual neutral atoms.Comment: 4 pages, 3 figure
A comparative study of deconvolution techniques for quantum-gas microscope images
Quantum-gas microscopes are used to study ultracold atoms in optical lattices
at the single particle level. In these system atoms are localised on lattice
sites with separations close to or below the diffraction limit. To determine
the lattice occupation with high fidelity, a deconvolution of the images is
often required. We compare three different techniques, a local iterative
deconvolution algorithm, Wiener deconvolution and the Lucy-Richardson
algorithm, using simulated microscope images. We investigate how the
reconstruction fidelity scales with varying signal-to-noise ratio, lattice
filling fraction, varying fluorescence levels per atom, and imaging resolution.
The results of this study identify the limits of singe-atom detection and
provide quantitative fidelities which are applicable for different atomic
species and quantum-gas microscope setups
Galactic microwave emission at degree angular scales
We cross-correlate the Saskatoon Ka and Q-Band Cosmic Microwave Background
(CMB) data with different maps to quantify possible foreground contamination.
We detect a marginal correlation (2 sigma) with the Diffuse Infrared Background
Experiment (DIRBE) 240, 140 and 100 microm maps, but we find no significant
correlation with point sources, with the Haslam 408 MHz map or with the Reich
and Reich 1420 MHz map. The rms amplitude of the component correlated with
DIRBE is about 20% of the CMB signal. Interpreting this component as free-free
emission, this normalization agrees with that of Kogut et al. (1996a; 1996b)
and supports the hypothesis that the spatial correlation between dust and warm
ionized gas observed on large angular scales persists to smaller angular
scales. Subtracting this contribution from the CMB data reduces the
normalization of the Saskatoon power spectrum by only a few percent.Comment: Minor revisions to match published version. 14 pages, with 2 figures
included. Color figure and links at
http://www.sns.ias.edu/~angelica/foreground.htm
Large-Scale QSO-Galaxy Correlations and Weak Lensing
Several recent studies show that bright, intermediate and high redshift
optically and radio selected QSOs are positively correlated with nearby
galaxies on a range of angular scales up to a degree. Obscuration by unevenly
distributed Galactic dust can be ruled out as the cause, leaving weak
statistical lensing as the physical process responsible. However the amplitude
of correlations on < 1 degree scales is at least a factor of a few larger than
lensing model predictions. A possible way to reconcile the observations and
theory is to revise the weak lensing formalism. We extend the standard lensing
formulation to include the next higher order term (second order) in the
geodesic equation of motion for photons. We derive relevant equations
applicable in the weak lensing regime, and discuss qualitative properties of
the updated formulation. We then perform numerical integrations of the revised
equation and study the effect of the extra term using two different types of
cosmic mass density fluctuations. We find that nearby large-scale coherent
structures increase the amplitude of the predicted lensing-induced correlations
between QSOs and foreground galaxies by ~ 10% (not a factor of several required
by observations), while the redshift of the optimal, i.e. `most correlated'
structures is moved closer to the observer compared to what is predicted using
the standard lensing equation.Comment: extended Section 2; 20 pages, including 4 figures, accepted to Ap
The Tenerife Cosmic Microwave Background Maps: Observations and First Analysis
The results of the Tenerife Cosmic Microwave Background (CMB) experiments are
presented. These observations cover 5000 and 6500 square degrees on the sky at
10 and 15 GHz respectively centred around Dec.~ +35 degrees. The experiments
are sensitive to multipoles l=10-30 which corresponds to the Sachs-Wolfe
plateau of the CMB power spectra. The sensitivity of the results are ~31 and
\~12 microK at 10 and 15 GHz respectively in a beam-size region (5 degrees
FWHM). The data at 15 GHz show clear detection of structure at high Galactic
latitude; the results at 10 GHz are compatible with these, but at lower
significance. A likelihood analysis of the 10 and 15 GHz data at high Galactic
latitude, assuming a flat CMB band power spectra gives a signal Delta
T_l=30+10-8 microK (68 % C.L.). Including the possible contaminating effect due
to the diffuse Galactic component, the CMB signal is Delta T_l=30+15-11 microK.
These values are highly stable against the Galactic cut chosen. Assuming a
Harrison-Zeldovich spectrum for the primordial fluctuations, the above values
imply an expected quadrupole Q_RMS-PS=20+10-7 microK which confirms previous
results from these experiments, and which are compatible with the COBE DMR.Comment: 17 pages, 7 figures. Submitted to Ap
Cm-Wavelength Total Flux and Linear Polarization Properties of Radio-Loud BL Lacertae Objects
Results from a long-term program to quantify the range of behavior of the
cm-wavelength total flux and linear polarization variability properties of a
sample of 41 radio-loud BL Lac objects using weekly to tri-monthly observations
with the University of Michigan 26-m telescope operating at 14.5, 8.0, and 4.8
GHz are presented; these observations are used to identify class-dependent
differences between these BL Lacs and QSOs in the Pearson-Readhead sample. The
BL Lacs are found to be more highly variable in total flux density than the
QSOs, exhibiting changes that are often nearly-simultaneous and of comparable
amplitude at 14.5 and 4.8 GHz in contrast to the behavior in the QSOs and
supporting the existence of class-dependent differences in opacity within the
parsec-scale jet flows. Structure function analyses of the flux observations
quantify that a characteristic timescale is identifiable in only 1/3 of the BL
Lacs. The time-averaged fractional linear polarizations are only on the order
of a few percent and are consistent with the presence of tangled magnetic
fields within the emitting regions. In many sources a preferred long-term
orientation of the EVPA is present; when compared with the VLBI structural
axis, no preferred position angle difference is identified. The polarized flux
typically exhibits variability with timescales of months to a few years and
shows the signature of a propagating shock during several resolved outbursts.
The observations indicate that the source emission is predominately due to
evolving source components and support the occurrence of more frequent shock
formation in BL Lac parsec-scale flows than in QSO jets. The differences in
variability behavior and polarization between BL Lacs and QSOs can be explained
by differences in jet stability.Comment: 1 LaTex (aastex) file, 21 postscript figure files, 2 external LaTex
table files. To appear in the Astrophysical Journa
New Cosmological Structures on Medium Angular Scales Detected with the Tenerife Experiments
We present observations at 10 and 15 GHz taken with the Tenerife experiments
in a band of the sky at Dec.=+35 degrees. These experiments are sensitive to
multipoles in the range l=10-30. The sensitivity per beam is 56 and 20 microK
for the 10 and the 15 GHz data, respectively. After subtraction of the
prediction of known radio-sources, the analysis of the data at 15 GHz at high
Galactic latitude shows the presence of a signal with amplitude Delta Trms ~ 32
microK. In the case of a Harrison-Zeldovich spectrum for the primordial
fluctuations, a likelihood analysis shows that this signal corresponds to a
quadrupole amplitude Q_rms-ps=20.1+7.1-5.4 microK, in agreement with our
previous results at Dec.+=40 degrees and with the results of the COBE DMR.
There is clear evidence for the presence of individual features in the RA range
190 degrees to 250 degrees with a peak to peak amplitude of ~110 microK. A
preliminary comparison between our results and COBE DMR predictions for the
Tenerife experiments clearly indicates the presence of individual features
common to both. The constancy in amplitude over such a large range in frequency
(10-90 GHz) is strongly indicative of an intrinsic cosmological origin for
these structures.Comment: ApJ Letters accepted, 13 pages Latex (uses AASTEX) and 4 encapsulated
postscript figures
Chandra and HST observations of gamma-ray blazars: comparing jet emission at small and large scales
We present new Chandra and HST data for four gamma-ray blazars selected on
the basis of radio morphology with the aim of revealing X-ray and optical
emission from their jets at large scales. All the sources have been detected.
Spectral Energy Distributions of the large scale jets are obtained as well as
new X-ray spectra for the blazar cores. Modeling for each object the core
(sub-pc scale) and large-scale (>100 kpc) jet SEDs, we derive the properties of
the same jet at the two scales. The comparison of speeds and powers at
different scales supports a simple scenario for the dynamics and propagation of
high power relativistic jets.Comment: Accepted for publication in Ap
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