784 research outputs found
Adaptive clustering procedure for continuous gravitational wave searches
In hierarchical searches for continuous gravitational waves, clustering of
candidates is an important postprocessing step because it reduces the number of
noise candidates that are followed-up at successive stages [1][7][12]. Previous
clustering procedures bundled together nearby candidates ascribing them to the
same root cause (be it a signal or a disturbance), based on a predefined
cluster volume. In this paper, we present a procedure that adapts the cluster
volume to the data itself and checks for consistency of such volume with what
is expected from a signal. This significantly improves the noise rejection
capabilities at fixed detection threshold, and at fixed computing resources for
the follow-up stages, this results in an overall more sensitive search. This
new procedure was employed in the first Einstein@Home search on data from the
first science run of the advanced LIGO detectors (O1) [11].Comment: 11 pages, 9 figures, 2 tables; v1: initial submission; v2: journal
review, copyedited version; v3: fixed typo in Fig
A soft X ray plane grating monochromator optimized for elliptical dipole radiation from modern sources
Abstract We describe a new but yet well proven way of making elliptically polarized dipole radiation from the BESSY II storage ring applicable to the SX700 type collimated plane grating monochromator PM3. We show that due to the limited vertical acceptance of the grating a simple use of vertical apertures is not possible in this case. Rather, deflecting the beam up or downwards by rotating the vertically collimating toroidal mirror M1 around the light axis leads to an excellent performance. The resulting detune of the photon energy can be taken into account by a readjustment of the monochromator internal plane mirror M2. The energy resolution of the beamline is not affected by the non zero roll of the collimating mirro
Identification and removal of non-Gaussian noise transients for gravitational wave searches
We present a new method to remove non-Gaussian noise transients in gravitational wave data. The method does not rely on any a-priori knowledge on the amplitude or duration of the transient events. In light of the character of the newly released LIGO O3a data, glitch-identification is particularly relevant for searches using this data. Our method preserves more data than previously achieved, while obtaining the same, if not higher, noise reduction. We achieve a 2-fold reduction in zeroed-out data with respect to the gates released by LIGO on the O3a data. We describe the method and characterise its performance. While developed in the context of searches for continuous signals, this method can be used to prepare gravitational wave data for any search. As the cadence of compact binary inspiral detections increases and the lower noise level of the instruments unveils new glitches, excising disturbances effectively, precisely, and in a timely manner, becomes more important. Our method does this. We release the source code associated with this new technique and the gates for the newly released O3 data
Density-clustering of continuous gravitational wave candidates from large surveys
Searches for continuous gravitational waves target nearly monochromaticgravitational wave emission from e.g. non-axysmmetric fast-spinning neutronstars. Broad surveys often require to explicitly search for a very large numberof different waveforms, easily exceeding templates. In suchcases, for practical reasons, only the top, say , results aresaved and followed-up through a hierarchy of stages. Most of these candidatesare not completely independent of neighbouring ones, but arise due to somecommon cause: a fluctuation, a signal or a disturbance. By judiciouslyclustering together candidates stemming from the same root cause, thesubsequent follow-ups become more effective. A number of clustering algorithmshave been employed in past searches based on iteratively finding symmetric andcompact over-densities around candidates with high detection statistic values.The new clustering method presented in this paper is a significant improvementover previous methods: it is agnostic about the shape of the over-densities, isvery efficient and it is effective: at a very high detection efficiency, it hasa noise rejection of , is capable of clustering two orders ofmagnitude more candidates than attainable before and, at fixed sensitivity itenables more than a factor of 30 faster follow-ups. We also demonstrate how tooptimally choose the clustering parameters.<br
Loosely coherent search in LIGO O1 data for continuous gravitational waves from Terzan 5 and the galactic center
We report results of a search for continuous gravitational waves from a
region covering the globular cluster Terzan 5 and the galactic center.
Continuous gravitational waves are expected from fast-spinning, slightly
non-axisymmetric isolated neutron stars as well as more exotic objects. The
regions that we target are believed to be unusually abundant in neutron stars.
We use a new loosely coherent search method that allows to reach unprecedented
levels of sensitivity for this type of search. The search covers the frequency
band 475-1500 Hz and frequency time derivatives in the range of [-3e-8, +1e-9]
Hz/s, which is a parameter range not explored before with the depth reached by
this search.
As to be expected with only a few months of data from the same observing run,
it is very difficult to make a confident detection of a continuous signal over
such a large parameter space. A list of parameter space points that passed all
the thresholds of this search is provided. We follow-up the most significant
outlier on the newly released O2 data and cannot confirm it. We provide upper
limits on the gravitational wave strength of signals as a function of signal
frequency
An Einstein@home search for continuous gravitational waves from Cassiopeia A
We report the results of a directed search for continuous gravitational-wave
emission in a broad frequency range (between 50 and 1000 Hz) from the central
compact object of the supernova remnant Cassiopeia A (Cas A). The data comes
from the sixth science run of LIGO and the search is performed on the volunteer
distributed computing network Einstein@Home. We find no significant signal
candidate, and set the most constraining upper limits to date on the
gravitational-wave emission from Cas A, which beat the indirect age-based upper
limit across the entire search range. At around 170 Hz (the most sensitive
frequency range), we set 90% confidence upper limits on the gravitational wave
amplitude of , roughly twice as constraining
as the upper limits from previous searches on Cas A. The upper limits can also
be expressed as constraints on the ellipticity of Cas A; with a few reasonable
assumptions, we show that at gravitational-wave frequencies greater than
300~Hz, we can exclude an ellipticity of .Comment: 29 pages, 7 figures, 3 table
Results from an Einstein@Home search for continuous gravitational waves from Cassiopeia A, Vela Jr. and G347.3
We report results of the most sensitive search to date for periodic
gravitational waves from Cassiopeia A, Vela Jr. and G347.3 with frequency
between 20 and 1500 Hz. The search was made possible by the computing power
provided by the volunteers of the Einstein@Home project and improves on
previous results by a factor of 2 across the entire frequency range for all
targets. We find no significant signal candidate and set the most stringent
upper limits to date on the amplitude of gravitational wave signals from the
target population, corresponding to sensitivity depths between 54 and 83 , depending on the
target and the frequency range. At the frequency of best strain sensitivity,
near Hz, we set 90% confidence upper limits on the gravitational wave
intrinsic amplitude of , probing ellipticity values
for Vela Jr. as low as , assuming a distance of 200 pc
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