2,508 research outputs found
Cross-Correlation analysis of WMAP and EGRET in Wavelet Space
We cross correlate the Wilkinson Microwave Anisotropy Probe (WMAP) first year
data and the diffuse gamma-ray intensity maps from the Energetic Gamma Ray
Experiment Telescope (EGRET) using spherical wavelet approaches. Correlations
at 99.7% significance level have been detected, at scales around
in the WMAP foreground cleaned W-band and Q-band maps, based on data from
regions that are outside the most conservative WMAP foreground mask; no
significant correlation is found with the Tegmark cleaned map. The detected
correlation is most likely of Galactic origin, and thus can help us probing the
origins of possible Galactic foreground residuals and ultimately removing them
from measured microwave sky maps.Comment: 4 pages, 7 figures; accepted for publication in ApJ
A Limit on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales
A ground-based polarimeter, PIQUE, operating at 90 GHz has set a new limit on
the magnitude of any polarized anisotropy in the cosmic microwave background.
The combination of the scan strategy and full width half maximum beam of 0.235
degrees gives broad window functions with average multipoles, l = 211+294-146
and l = 212+229-135 for the E- and B-mode window functions, respectively. A
joint likelihood analysis yields simultaneous 95% confidence level flat band
power limits of 14 and 13 microkelvin on the amplitudes of the E- and B-mode
angular power spectra, respectively. Assuming no B-modes, a 95% confidence
limit of 10 microkelvin is placed on the amplitude of the E-mode angular power
spectrum alone.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter
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
No detectable radio emission from the magnetar-like pulsar in Kes 75
The rotation-powered pulsar PSR J1846-0258 in the supernova remnant Kes 75
was recently shown to have exhibited magnetar-like X-ray bursts in mid-2006.
Radio emission has not yet been observed from this source, but other
magnetar-like sources have exhibited transient radio emission following X-ray
bursts. We report on a deep 1.9 GHz radio observation of PSR J1846-0258 with
the 100-m Green Bank Telescope in late 2007 designed to search for radio
pulsations or bursts from this target. We have also analyzed three shorter
serendipitous 1.4 GHz radio observations of the source taken with the 64-m
Parkes telescope during the 2006 bursting period. We detected no radio emission
from PSR J1846-0258 in either the Green Bank or Parkes datasets. We place an
upper limit of 4.9 \mu Jy on coherent pulsed emission from PSR J1846-0258 based
on the 2007 November 2 observation, and an upper limit of 27 \mu Jy around the
time of the X-ray bursts. Serendipitously, we observed radio pulses from the
nearby RRAT J1846-02, and place a 3\sigma confidence level upper limit on its
period derivative of 1.7 * 10^{-13}, implying its surface dipole magnetic field
is less than 2.6 * 10^{13} G.Comment: 15 pages, 2 figures, submitted to Ap
Does tiny-scale atomic structure exist in the interstellar medium ?
We report on preliminary results from the recent multi-epoch neutral hydrogen
absorption measurements toward three pulsars, B0823+26, B1133+16 and B2016+28,
using the Arecibo telescope. We do not find significant variations in optical
depth profiles over periods of 0.3 and 9--10 yr, or on spatial scales of 10--20
and 70--85 AU. The large number of non detections of the tiny scale atomic
structure suggests that the AU-sized structure is not ubiquitous in the
interstellar medium and could be quite a rare phenomenon.Comment: Accepted by ApJ Letters, 5 pages, 2 figure
Evidence for a Weak Galactic Center Magnetic Field from Diffuse Low Frequency Nonthermal Radio Emission
New low-frequency 74 and 330 MHz observations of the Galactic center (GC)
region reveal the presence of a large-scale (6\arcdeg\times 2\arcdeg) diffuse
source of nonthermal synchrotron emission. A minimum energy analysis of this
emission yields a total energy of ergs
and a magnetic field strength of \muG (where is
the proton to electron energy ratio and is the filling factor of the
synchrotron emitting gas). The equipartition particle energy density is
\evcm, a value consistent with cosmic-ray data. However,
the derived magnetic field is several orders of magnitude below the 1 mG field
commonly invoked for the GC. With this field the source can be maintained with
the SN rate inferred from the GC star formation. Furthermore, a strong magnetic
field implies an abnormally low GC cosmic-ray energy density. We conclude that
the mean magnetic field in the GC region must be weak, of order 10 \muG (at
least on size scales \ga 125\arcsec).Comment: 12 pages, 1 JPEG figure, uses aastex.sty; Accepted for publication,
ApJL (2005, published
Global 21cm signal experiments: a designer's guide
[Abridged] The spatially averaged global spectrum of the redshifted 21cm line
has generated much experimental interest, for it is potentially a direct probe
of the Epoch of Reionization and the Dark Ages. Since the cosmological signal
here has a purely spectral signature, most proposed experiments have little
angular sensitivity. This is worrisome because with only spectra, the global
21cm signal can be difficult to distinguish from foregrounds such as Galactic
synchrotron radiation, as both are spectrally smooth and the latter is orders
of magnitude brighter. We establish a mathematical framework for global signal
data analysis in a way that removes foregrounds optimally, complementing
spectra with angular information. We explore various experimental design
trade-offs, and find that 1) with spectral-only methods, it is impossible to
mitigate errors that arise from uncertainties in foreground modeling; 2)
foreground contamination can be significantly reduced for experiments with fine
angular resolution; 3) most of the statistical significance in a positive
detection during the Dark Ages comes from a characteristic high-redshift trough
in the 21cm brightness temperature; and 4) Measurement errors decrease more
rapidly with integration time for instruments with fine angular resolution. We
show that if observations and algorithms are optimized based on these findings,
an instrument with a 5 degree beam can achieve highly significant detections
(greater than 5-sigma) of even extended (high Delta-z) reionization scenarios
after integrating for 500 hrs. This is in contrast to instruments without
angular resolution, which cannot detect gradual reionization. Abrupt ionization
histories can be detected at the level of 10-100's of sigma. The expected
errors are also low during the Dark Ages, with a 25-sigma detection of the
expected cosmological signal after only 100 hrs of integration.Comment: 34 pages, 30 figures. Replaced (v2) to match accepted PRD version
(minor pedagogical additions to text; methods, results, and conclusions
unchanged). Fixed two typos (v3); text, results, conclusions etc. completely
unchange
A Search for Sub-Millisecond Pulsars
We have conducted a search of 19 southern Galactic globular clusters for
sub-millisecond pulsars at 660 MHz with the Parkes 64-m radio telescope. To
minimize dispersion smearing we used the CPSR baseband recorder, which samples
the 20 MHz observing band at the Nyquist rate. By possessing a complete
description of the signal we could synthesize an optimal filterbank in
software, and in the case of globular clusters of known dispersion measure,
much of the dispersion could be removed using coherent techniques. This allowed
for very high time resolution (25.6 us in most cases), making our searches in
general sensitive to sub-millisecond pulsars with flux densities greater than
about 3 mJy at 50 cm. No new pulsars were discovered, placing important
constraints on the proportion of pulsars with very short spin periods in these
clusters.Comment: 8 pages, 3 figures, to appear in Ap
Joint Bayesian component separation and CMB power spectrum estimation
We describe and implement an exact, flexible, and computationally efficient
algorithm for joint component separation and CMB power spectrum estimation,
building on a Gibbs sampling framework. Two essential new features are 1)
conditional sampling of foreground spectral parameters, and 2) joint sampling
of all amplitude-type degrees of freedom (e.g., CMB, foreground pixel
amplitudes, and global template amplitudes) given spectral parameters. Given a
parametric model of the foreground signals, we estimate efficiently and
accurately the exact joint foreground-CMB posterior distribution, and therefore
all marginal distributions such as the CMB power spectrum or foreground
spectral index posteriors. The main limitation of the current implementation is
the requirement of identical beam responses at all frequencies, which restricts
the analysis to the lowest resolution of a given experiment. We outline a
future generalization to multi-resolution observations. To verify the method,
we analyse simple models and compare the results to analytical predictions. We
then analyze a realistic simulation with properties similar to the 3-yr WMAP
data, downgraded to a common resolution of 3 degree FWHM. The results from the
actual 3-yr WMAP temperature analysis are presented in a companion Letter.Comment: 23 pages, 16 figures; version accepted for publication in ApJ -- only
minor changes, all clarifications. More information about the WMAP3 analysis
available at http://www.astro.uio.no/~hke under the Research ta
Galactic emission at 19 GHz
We cross-correlate a 19 GHz full sky Cosmic Microwave Background (CMB) survey
with other maps to quantify the foreground contribution. Correlations are
detected with the Diffuse Infrared Background Experiment (DIRBE) 240, 140 and
100 micron maps at high latitudes (|b|>30degrees), and marginal correlations
are detected with the Haslam 408 MHz and the Reich & Reich 1420 MHz synchrotron
maps. The former agree well with extrapolations from higher frequencies probed
by the COBE DMR and Saskatoon experiments and are consistent with both
free-free and rotating dust grain emission.Comment: 4 pages, with 4 figures included. Accepted for publication in ApJL.
Color figure and links at http://www.sns.ias.edu/~angelica/foreground.html#19
or from [email protected]
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