4,913 research outputs found
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
Feedback-Optimized Operations with Linear Ion Crystals
We report on transport operations with linear crystals of 40Ca+ ions by
applying complex electric time-dependent potentials. For their control we use
the information obtained from the ions' fluorescence. We demonstrate that by
means of this feedback technique, we can transport a predefined number of ions
and also split and unify ion crystals. The feedback control allows for a robust
scheme, compensating for experimental errors as it does not rely on a precisely
known electrical modeling of the electric potentials in the ion trap
beforehand. Our method allows us to generate a self-learning voltage ramp for
the required process. With an experimental demonstration of a transport with
more than 99.8 % success probability, this technique may facilitate the
operation of a future ion based quantum processor
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
The blazar S5 0014+813: a real or apparent monster?
A strong hard X-ray luminosity from a blazar flags the presence of a very
powerful jet. If the jet power is in turn related to the mass accretion rate,
the most luminous hard X-ray blazars should pinpoint the largest accretion
rates, and therefore the largest black hole masses. These ideas are confirmed
by the Swift satellite observations of the blazar S5 0014+813, at the redshift
z=3.366. Swift detected this source with all its three instruments, from the
optical to the hard X-rays. Through the construction of its spectral energy
distribution we are confident that its optical-UV emission is thermal in
origin. Associating it to the emission of a standard optically thick
geometrically thin accretion disk, we find a black hole mass of 40 billion
solar masses, radiating at 40% the Eddington value. The derived mass is among
the largest ever found. Super-Eddington slim disks or thick disks with the
presence of a collimating funnel can in principle reduce the black hole mass
estimate, but tends to produce spectra bluer than observed.Comment: 5 pages, 2 figures, accepted for publication as a letter in MNRAS
after minor revisio
A Nanofiber-Based Optical Conveyor Belt for Cold Atoms
We demonstrate optical transport of cold cesium atoms over millimeter-scale
distances along an optical nanofiber. The atoms are trapped in a
one-dimensional optical lattice formed by a two-color evanescent field
surrounding the nanofiber, far red- and blue-detuned with respect to the atomic
transition. The blue-detuned field is a propagating nanofiber-guided mode while
the red-detuned field is a standing-wave mode which leads to the periodic axial
confinement of the atoms. Here, this standing wave is used for transporting the
atoms along the nanofiber by mutually detuning the two counter-propagating
fields which form the standing wave. The performance and limitations of the
nanofiber-based transport are evaluated and possible applications are
discussed
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
Exclusive measurement of coherent eta photoproduction from the deuteron
Coherent photoproduction of eta mesons from the deuteron has been measured
from threshold up to incident photon energies of 750 MeV using the photon
spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI.
For the first time, differential coherent cross sections have been deduced from
the coincident detection of the eta meson and the recoil deuteron. A missing
energy analysis was used for the suppression of background events so that a
very clean identification of coherent eta-photoproduction was achieved. The
resulting cross sections agree with previous experimental results except for
angles around 90 deg in the photon-deuteron cm-system where they are smaller.
They are compared to various model calculations.Comment: 4 pages, 4 figure
Magnetic Fields in Quasar Cores II
Multi-frequency polarimetry with the Very Long Baseline Array (VLBA)
telescope has revealed absolute Faraday Rotation Measures (RMs) in excess of
1000 rad/m/m in the central regions of 7 out of 8 strong quasars studied (e.g.,
3C 273, 3C 279, 3C 395). Beyond a projected distance of ~20 pc, however, the
jets are found to have |RM| < 100 rad/m/m. Such sharp RM gradients cannot be
produced by cluster or galactic-scale magnetic fields, but rather must be the
result of magnetic fields organized over the central 1-100 pc. The RMs of the
sources studied to date and the polarization properties of BL Lacs, quasars and
galaxies are shown to be consistent so far with the predictions of unified
schemes. The direct detection of high RMs in these quasar cores can explain the
low fractional core polarizations usually observed in quasars at centimeter
wavelengths as the result of irregularities in the Faraday screen on scales
smaller than the telescope beam. Variability in the RM of the core is reported
for 3C 279 between observations taken 1.5 years apart, indicating that the
Faraday screen changes on that timescale, or that the projected superluminal
motion of the inner jet components samples a new location in the screen with
time. Either way, these changes in the Faraday screen may explain the dramatic
variability in core polarization properties displayed by quasars.Comment: Accepted to the ApJ. 27 pages, 9 figures including figure 6 in colo
Range expansion with mutation and selection: dynamical phase transition in a two-species Eden model
The colonization of unoccupied territory by invading species, known as range expansion, is a spatially heterogeneous non-equilibrium growth process. We introduce a two-species Eden growth model to analyze the interplay between uni-directional (irreversible) mutations and selection at the expanding front. While the evolutionary dynamics leads to coalescence of both wild-type and mutant clusters, the non-homogeneous advance of the colony results in a rough front. We show that roughening and domain dynamics are strongly coupled, resulting in qualitatively altered bulk and front properties. For beneficial mutations the front is quickly taken over by mutants and growth proceeds Eden-like. In contrast, if mutants grow slower than wild-types, there is an antagonism between selection pressure against mutants and growth by the merging of mutant domains with an ensuing absorbing state phase transition to an all-mutant front. We find that surface roughening has a marked effect on the critical properties of the absorbing state phase transition. While reference models, which keep the expanding front flat, exhibit directed percolation critical behavior, the exponents of the two-species Eden model strongly deviate from it. In turn, the mutation-selection process induces an increased surface roughness with exponents distinct from that of the classical Eden model
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