5,037 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
Capture and release of a conditional state of a cavity QED system by quantum feedback
Detection of a single photon escaping an optical cavity QED system prepares a nonclassical state of the electromagnetic field. The evolution of the state can be modified by changing the drive of the cavity. For the appropriate feedback, the conditional state can be captured (stabilized) and then released. This is observed by a conditional intensity measurement that shows suppression of vacuum Rabi oscillations for the length of the feedback pulse and their subsequent return
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
Hematopoietic cell transplantation provides an immune-tolerant platform for myoblast transplantation in dystrophic dogs.
Duchenne Muscular Dystrophy (DMD) is the most common and severe form of muscular dystrophy in humans. The goal of myogenic stem cell transplant therapy for DMD is to increase dystrophin expression in existing muscle fibers and to provide a source of stem cells for future muscle generation. Although syngeneic myogenic stem cell transplants have been successful in mice, allogeneic transplants of myogenic stem cells were ineffective in several human trials. To determine whether allogeneic muscle progenitor cells can be successfully transplanted in an immune-tolerant recipient, we induced immune tolerance in two DMD-affected (cxmd) dogs through hematopoietic cell transplantation (HCT). Injection of freshly isolated muscle-derived cells from the HCT donor into either fully or partially chimeric xmd recipients restored dystrophin expression up to 6.48% of wild-type levels, reduced the number of centrally located nuclei, and improved muscle structure. Dystrophin expression was maintained for at least 24 weeks. Taken together, these data indicate that immune tolerance to donor myoblasts provides an important platform from which to further improve myoblast transplantation, with the goal of restoring dystrophin expression to patients with DMD
Hard X-ray detection of the high redshift quasar 4C 71.07
BATSE/OSSE observations of the high redshift quasar 4C 71.07 indicate that
this is the brightest and furthest AGN so far detected above 20 keV. BATSE
Earth occultation data have been used to search for emission from 4C 71.07 from
nearly 3 years of observation. The mean source flux over the whole period in
the BATSE energy range 20-100 keV is (13.2 +/- 1.06) x 10^(-11) erg cm^(-2)
s^(-1) corresponding to a luminosity of 2 x 10^(48) erg s^(-1). The BATSE light
curve over the 3 years of observations shows several flare-like events, one of
which (in January 1996) is associated with an optical flare (R=16.1) but with a
delay of 55 days. The OSSE/BATSE spectral analysis indicates that the source is
characterized by a flat power spectrum (Gamma about 1.1 - 1.3) when in a low
state; this spectral form is consistent within errors with the ASCA and ROSAT
spectra. This means that the power law observed from 0.1 to 10 keV extends up
to at least 1 MeV but steepens soon after to meet EGRET high energy data. BATSE
data taken around the January 1996 flare suggests that the spectrum could be
steeper when the source is in a bright state. The nuF-nu representation of the
source is typical of a low frequency peaked/gamma-ray dominated blazar, with
the synchrotron peak in the mm-FIR band and the Compton peak in the MeV band.
The BATSE and OSSE spectral data seem to favour a model in which the high
energy flux is due to the sum of the synchrotron self-Compton and the external
Compton contributions; this is also supported by the variability behaviour of
the source.Comment: 19 pages, LaTeX, plus 4 .ps figures. accepted by Astrophysical
Journa
Effects of Foreground Contamination on the Cosmic Microwave Background Anisotropy Measured by MAP
We study the effects of diffuse Galactic, far-infrared extragalactic source,
and radio point source emission on the cosmic microwave background (CMB)
anisotropy data anticipated from the MAP experiment. We focus on the
correlation function and genus statistics measured from mock MAP
foreground-contaminated CMB anisotropy maps generated in a spatially-flat
cosmological constant dominated cosmological model. Analyses of the simulated
MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground
effects on the correlation function are small compared with cosmic variance.
However, the Galactic emission, even just from the region with |b| > 20 deg,
significantly affects the topology of CMB anisotropy, causing a negative genus
shift non-Gaussianity signal. Given the expected level of cosmic variance, this
effect can be effectively reduced by subtracting existing Galactic foreground
emission models from the observed data. IRAS and DIRBE far-infrared
extragalactic sources have little effect on the CMB anisotropy. Radio point
sources raise the amplitude of the correlation function considerably on scales
below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit
effectively eliminates this effect. Radio sources also result in a positive
genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate
radio point source data is essential for an unambiguous detection of CMB
anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological
origin can be detected from the foreground-subtracted CMB anisotropy map at the
2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04)
or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3
(1.0) deg FWHM scale.Comment: 26 pages, 7 figures, Accepted for Publication in Astrophysical
Journal (Some sentences and figures modified
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
Extragalactic Point Source Search in WMAP 61 and 94 GHz Data
We report the results of an extragalactic point source search using the 61
and 94 GHz (V- and W-band) temperature maps from the Wilkinson Microwave
Anisotropy Probe (WMAP). Applying a method that cancels the ``noise'' due to
the CMB anisotropy signal, we find in the |b| > 10\degr region 31 sources in
the first-year maps and 64 sources in the three-year co-added maps, at a
level. The 1 position uncertainties are 1.6' and 1.4' each.
The increased detections and improved positional accuracy are expected from the
higher signal-to-noise ratio of WMAP three-year data. All sources detected in
the first-year maps are repeatedly detected in the three-year maps, which is a
strong proof of the consistency and reliability of this method. Among all the
detections, 21 are new, i.e. not in the WMAP three-year point source catalog.
We associate all but two of them with known objects. The two unidentified
sources are likely to be variable or extended as observations through VLA,
CARMA and ATCA all show non-detection at the nominal locations. We derive the
source count distribution at WMAP V-band by combining our verified detections
with sources from the WMAP three-year catalog. Assuming the effect of source
clustering is negligible, the contribution to the power spectrum from faint
sources below 0.75 Jy is estimated to be
sr for V-band, which implies a source correction amplitude sr.Comment: 22 pages, 10 figures, submitted to ApJ; Typo corrected in the
uncertainty of kappa in the Discussion, and a correction to the description
of the smoothing function in Methodolog
Implications of a 125 GeV Higgs scalar for LHC SUSY and neutralino dark matter searches
The ATLAS and CMS collaborations have reported an excess of events in the
\gamma\gamma, ZZ^*\to 4\ell and WW^* search channels at an invariant mass m
\simeq 125 GeV, which could be the first evidence for the long-awaited Higgs
boson. We investigate the consequences of requiring m_h\simeq 125 GeV in both
the mSUGRA and NUHM2 SUSY models. In mSUGRA, large values of trilinear soft
breaking parameter |A_0| are required, and universal scalar m_0\agt 0.8 TeV is
favored so that we expect squark and slepton masses typically in the multi-TeV
range. This typically gives rise to an "effective SUSY" type of sparticle mass
spectrum. In this case, we expect gluino pair production as the dominant
sparticle creation reaction at LHC. For m_0< 5 TeV, the superpotential
parameter \mu > 2 TeV and m_A> 0.8 TeV, greatly restricting neutralino
annihilation mechanisms. These latter conclusions are softened if m_0\sim 10-20
TeV or if one proceeds to the NUHM2 model. The standard neutralino abundance
tends to be far above WMAP-measured values unless the neutralino is
higgsino-like. We remark upon possible non-standard (but perhaps more
attractive) cosmological scenarios which can bring the predicted dark matter
abundance into accord with the measured value, and discuss the implications for
direct and indirect detection of neutralino cold dark matter.Comment: 24 pages including 23 .eps figures; updated version 3 contains also
b-> tau+nu branching fractio
Neutral Hydrogen 21cm Absorption at Redshift 0.673 towards 1504+377
We detect the 21 cm line of neutral hydrogen in absorption at a redshift of
0.673 towards the 1 Jy radio source 1504+377. The 1504+377 radio source is
located toward the center of what appears to be an inclined disk galaxy at z =
0.674. The 21 cm absorption line shows multiple velocity components over a
velocity range of about 100 km sec, with a total HI column density:
N(HI) = cm. The
velocity-integrated optical depth of this system is the largest yet seen for
redshifted HI 21 cm absorption line systems (Carilli 1995). The 21 cm
absorption line is coincident in redshift with a previously detected broad
molecular absorption line system (Wiklind and Combes 1996). We do not detect HI
21 cm absorption associated with the narrow molecular absorption line system at
z = 0.67150, nor do we detect absorption at these redshifts by the 18 cm lines
of OH, nor by the 2 cm transition of HCO. There is no evidence for a bright
optical AGN in 1504+377, suggesting significant obscuration through the disk --
a hypothesis supported by the strong absorption observed. The 1504+377 system
resembles the ``red quasar'' PKS 1413+135, which has been modeled as a
optically obscured AGN with a very young radio jet in the center of a gas rich
disk galaxy (Perlman et al. 1996). The presence of very bright radio jets at
the centers of these two disk galaxies presents a challenge to unification
schemes for extragalactic radio sources and to models for the formation of
radio loud AGN.Comment: 17 pages, postscrip
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