2,024 research outputs found
Gravitoastronomy with neutron stars
Recent advances in gravitational wave detectors mean that we can start to make astrophysically important
statements about the physics of neutron stars based on observed upper limits to their gravitational luminosity.
Here we consider statements we can already make about a selection of known radio pulsars, based on data from
the LIGO and GEO600 detectors, and look forward to what could be learned from the first detections
Gravitational waves found again: here’s how they could whisper the universe’s secrets
The international team of physicists and astronomers responsible for the discovery of gravitational waves back in February has announced the detection of a second strong signal from the depths of space. It is further confirmation that gravitational waves both exist and tell us a whole new story about how the universe came to be the way it is
Digital Preservation and Astronomy: Lessons for funders and the funded
Astronomy looks after its data better than most disciplines, and it is no
coincidence that the consensus standard for the archival preservation of all
types of digital assets -- the OAIS Reference Model -- emerged originally from
the space science community.
It is useful to highlight both what is different about astronomy (and indeed
about Big Science in general), what could be improved, and what is exemplary,
and in the process I will give a brief introduction to the framework of the
OAIS model, and its useful conceptual vocabulary. I will illustrate this with a
discussion of the spectrum of big-science data management practices from
astronomy, through gravitational wave (GW) data, to particle physics.Comment: 4 pages, 1 figure, to appear in proceedings of ADASS XX; corresponds
to LIGO document P100017
Binary system delays and timing noise in searches for gravitational waves from known pulsars
The majority of fast millisecond pulsars are in binary systems, so that any
periodic signal they emit is modulated by both Doppler and relativistic
effects. Here we show how well-established binary models can be used to account
for these effects in searches for gravitational waves from known pulsars within
binary systems. A seperate issue affecting certain pulsar signals is that of
timing noise and we show how this, with particular reference to the Crab
pulsar, can be compensated for by using regularly updated timing ephemerides.Comment: 10 pages, 11 figures, accepted by Phys. Rev.
Bayesian estimation of pulsar parameters from gravitational wave data
We present a method of searching for, and parameterizing, signals from known
radio pulsars in data from interferometric gravitational wave detectors. This
method has been applied to data from the LIGO and GEO 600 detectors to set
upper limits on the gravitational wave emission from several radio pulsars.
Here we discuss the nature of the signal and the performance of the technique
on simulated data. We show how to perform a coherent multiple detector analysis
and give some insight in the covariance between the signal parameters.Comment: 9 pages, 6 figures. Accepted to Phys. Rev. D. A few small changes
from previous versio
A generalised Measurement Equation and van Cittert-Zernike theorem for wide-field radio astronomical interferometry
We derive a generalised van Cittert-Zernike (vC-Z) theorem for radio
astronomy that is valid for partially polarized sources over an arbitrarily
wide field-of-view (FoV). The classical vC-Z theorem is the theoretical
foundation of radio astronomical interferometry, and its application is the
basis of interferometric imaging. Existing generalised vC-Z theorems in radio
astronomy assume, however, either paraxiality (narrow FoV) or scalar
(unpolarized) sources. Our theorem uses neither of these assumptions, which are
seldom fulfilled in practice in radio astronomy, and treats the full
electromagnetic field. To handle wide, partially polarized fields, we extend
the two-dimensional electric field (Jones vector) formalism of the standard
"Measurement Equation" of radio astronomical interferometry to the full
three-dimensional formalism developed in optical coherence theory. The
resulting vC-Z theorem enables all-sky imaging in a single telescope pointing,
and imaging using not only standard dual-polarized interferometers (that
measure 2-D electric fields), but also electric tripoles and electromagnetic
vector-sensor interferometers. We show that the standard 2-D Measurement
Equation is easily obtained from our formalism in the case of dual-polarized
antenna element interferometers. We find, however, that such dual-polarized
interferometers can have polarimetric aberrations at the edges of the FoV that
are often correctable. Our theorem is particularly relevant to proposed and
recently developed wide FoV interferometers such as LOFAR and SKA, for which
direction-dependent effects will be important.Comment: To be published in MNRA
Managing Research Data in Big Science
The project which led to this report was funded by JISC in 2010--2011 as part of its 'Managing Research Data' programme, to examine the way in which Big Science data is managed, and produce any recommendations which may be appropriate. Big science data is different: it comes in large volumes, and it is shared and exploited in ways which may differ from other disciplines. This project has explored these differences using as a case-study Gravitational Wave data generated by the LSC, and has produced recommendations intended to be useful variously to JISC, the funding council (STFC) and the LSC community. In Sect. 1 we define what we mean by 'big science', describe the overall data culture there, laying stress on how it necessarily or contingently differs from other disciplines. In Sect. 2 we discuss the benefits of a formal data-preservation strategy, and the cases for open data and for well-preserved data that follow from that. This leads to our recommendations that, in essence, funders should adopt rather light-touch prescriptions regarding data preservation planning: normal data management practice, in the areas under study, corresponds to notably good practice in most other areas, so that the only change we suggest is to make this planning more formal, which makes it more easily auditable, and more amenable to constructive criticism. In Sect. 3 we briefly discuss the LIGO data management plan, and pull together whatever information is available on the estimation of digital preservation costs. The report is informed, throughout, by the OAIS reference model for an open archive
Managing Research Data: Gravitational Waves
The project which led to this report was funded by JISC in 2010–2011 as part of its
‘Managing Research Data’ programme, to examine the way in which Big Science data
is managed, and produce any recommendations which may be appropriate.
Big science data is different: it comes in large volumes, and it is shared and
exploited in ways which may differ from other disciplines. This project has explored
these differences using as a case-study Gravitational Wave data generated by the LSC,
and has produced recommendations intended to be useful variously to JISC, the funding
council (STFC) and the LSC community.
In Sect. 1 we define what we mean by ‘big science’, describe the overall data
culture there, laying stress on how it necessarily or contingently differs from other
disciplines.
In Sect. 2 we discuss the benefits of a formal data-preservation strategy, and the
cases for open data and for well-preserved data that follow from that. This leads to our
recommendations that, in essence, funders should adopt rather light-touch prescriptions
regarding data preservation planning: normal data management practice, in the areas
under study, corresponds to notably good practice in most other areas, so that the only
change we suggest is to make this planning more formal, which makes it more easily
auditable, and more amenable to constructive criticism.
In Sect. 3 we briefly discuss the LIGO data management plan, and pull together
whatever information is available on the estimation of digital preservation costs.
The report is informed, throughout, by the OAIS reference model for an open
archive. Some of the report’s findings and conclusions were summarised in [1].
See the document history on page 37
A fast search strategy for gravitational waves from low-mass X-ray binaries
We present a new type of search strategy designed specifically to find
continuously emitting gravitational wave sources in known binary systems based
on the incoherent sum of frequency modulated binary signal sidebands. The
search pipeline can be divided into three stages: the first is a wide
bandwidth, F-statistic search demodulated for sky position. This is followed by
a fast second stage in which areas in frequency space are identified as signal
candidates through the frequency domain convolution of the F-statistic with an
approximate signal template. For this second stage only precise information on
the orbit period and approximate information on the orbital semi-major axis are
required apriori. For the final stage we propose a fully coherent Markov chain
monte carlo based follow up search on the frequency subspace defined by the
candidates identified by the second stage. This search is particularly suited
to the low-mass X-ray binaries, for which orbital period and sky position are
typically well known and additional orbital parameters and neutron star spin
frequency are not. We note that for the accreting X-ray millisecond pulsars,
for which spin frequency and orbital parameters are well known, the second
stage can be omitted and the fully coherent search stage can be performed. We
describe the search pipeline with respect to its application to a simplified
phase model and derive the corresponding sensitivity of the search.Comment: 13 pages, 3 figures, to appear in the GWDAW 11 conference proceeding
Searching for gravitational waves from the Crab pulsar - the problem of timing noise
Of the current known pulsars, the Crab pulsar (B0531+21) is one of the most
promising sources of gravitational waves. The relatively large timing noise of
the Crab causes its phase evolution to depart from a simple spin-down model.
This effect needs to be taken in to account when performing time domain
searches for the Crab pulsar in order to avoid severely degrading the search
efficiency. The Jodrell Bank Crab pulsar ephemeris is examined to see if it can
be used for tracking the phase evolution of any gravitational wave signal from
the pulsar, and we present a method of heterodyning the data that takes account
of the phase wander. The possibility of obtaining physical information about
the pulsar from comparisons of the electromagnetically and a gravitationally
observed timing noise is discussed. Finally, additional problems caused by
pulsar glitches are discussed.Comment: 5 pages, 1 figure, Proceedings of the 5th Amaldi Conference on
Gravitational Waves, Pisa, Italy, 6-11 July 200
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