2,546 research outputs found
Optical Observations of the Binary Millisecond Pulsars J2145-0750 and J0034-0534
We report on optical observations of the low-mass binary millisecond pulsar
systems J0034-0534 and J2145-0750. A faint (I=23.5) object was found to be
coincident with the timing position of PSR J2145-0750. While a galaxy or
distant main-sequence star cannot be ruled out, its magnitude is consistent
with an ancient white dwarf, as expected from evolutionary models. For PSR
J0034-0534 no objects were detected to a limiting magnitude of R=25.0,
suggesting that the white dwarf in this system is cold. Using white dwarf
cooling models, the limit on the magnitude of the PSR J0034-0534 companion
suggests that at birth the pulsar in this system may have rotated with a period
as short as 0.6 ms. These observations provide further evidence that the
magnetic fields of millisecond pulsars do not decay on time scales shorter than
1 Gyr.Comment: 6 pages, uuencoded, gz -9 compressed postscript, accepted by ApJ
DASI Three-Year Cosmic Microwave Background Polarization Results
We present the analysis of the complete 3-year data set obtained with the
Degree Angular Scale Interferometer (DASI) polarization experiment, operating
from the Amundsen-Scott South Pole research station. Additional data obtained
at the end of the 2002 Austral winter and throughout the 2003 season were added
to the data from which the first detection of polarization of the cosmic
microwave background radiation was reported. The analysis of the combined data
supports, with increased statistical power, all of the conclusions drawn from
the initial data set. In particular, the detection of E-mode polarization is
increased to 6.3 sigma confidence level, TE cross-polarization is detected at
2.9 sigma, and B-mode polarization is consistent with zero, with an upper limit
well below the level of the detected E-mode polarization. The results are in
excellent agreement with the predictions of the cosmological model that has
emerged from CMB temperature measurements. The analysis also demonstrates that
contamination of the data by known sources of foreground emission is
insignificant.Comment: 13 pages Latex, 10 figures, submitted to Ap
A Sunyaev-Zel'dovich Effect Survey for High Redshift Clusters
Interferometric observations of the Sunyaev-Zel'dovich Effect (SZE) toward
clusters of galaxies provide sensitive cosmological probes. We present results
from 1 cm observations (at BIMA and OVRO) of a large, intermediate redshift
cluster sample. In addition, we describe a proposed, higher sensitivity array
which will enable us to survey large portions of the sky. Simulated
observations indicate that we will be able to survey one square degree of sky
per month to sufficient depth that we will detect all galaxy clusters more
massive than 2x10^{14} h^{-1}_{50}M_\odot, regardless of their redshift. We
describe the cluster yield and resulting cosmological constraints from such a
survey.Comment: 7 pages, 6 figures, latex, contribution to VLT Opening Symposiu
Parameter Estimation from Improved Measurements of the Cosmic Microwave Background from QUaD
We evaluate the contribution of cosmic microwave background (CMB) polarization spectra to cosmological parameter constraints. We produce cosmological parameters using high-quality CMB polarization data from the ground-based QUaD experiment and demonstrate for the majority of parameters that there is significant improvement on the constraints obtained from satellite CMB polarization data. We split a multi-experiment CMB data set into temperature and polarization subsets and show that the best-fit confidence regions for the ΛCDM six-parameter cosmological model are consistent with each other, and that polarization data reduces the confidence regions on all parameters. We provide the best limits on parameters from QUaD EE/BB polarization data and we find best-fit parameters from the multi-experiment CMB data set using the optimal pivot scale of k_p = 0.013 Mpc^(–1) to be {h^2Ω_c, h^2Ω_b, H_0, A_s, n_s, τ} = {0.113, 0.0224, 70.6, 2.29 × 10^(–9), 0.960, 0.086}
Cosmological Parameter Extraction from the First Season of Observations with DASI
The Degree Angular Scale Interferometer (\dasi) has measured the power
spectrum of the Cosmic Microwave Background anisotropy over the range of
spherical harmonic multipoles 100<l<900. We compare this data, in combination
with the COBE-DMR results, to a seven dimensional grid of adiabatic CDM models.
Adopting the priors h>0.45 and 0.0<=tau_c<=0.4, we find that the total density
of the Universe Omega_tot=1.04+/-0.06, and the spectral index of the initial
scalar fluctuations n_s=1.01+0.08-0.06, in accordance with the predictions of
inflationary theory. In addition we find that the physical density of baryons
Omega_b.h^2=0.022+0.004-0.003, and the physical density of cold dark matter
Omega_cdm.h^2=0.14+/-0.04. This value of Omega_b.h^2 is consistent with that
derived from measurements of the primordial abundance ratios of the light
elements combined with big bang nucleosynthesis theory. Using the result of the
HST Key Project h=0.72+/-0.08 we find that Omega_t=1.00+/-0.04, the matter
density Omega_m=0.40+/-0.15, and the vacuum energy density
Omega_lambda=0.60+/-0.15. (All 68% confidence limits.)Comment: 7 pages, 4 figures, minor changes in response to referee comment
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
Polarization Diffusion from Spacetime Uncertainty
A model of Lorentz invariant random fluctuations in photon polarization is
presented. The effects are frequency dependent and affect the polarization of
photons as they propagate through space. We test for this effect by confronting
the model with the latest measurements of polarization of Cosmic Microwave
Background (CMB) photons.Comment: 4 pages, 1 figur
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