| 1. |
- Aasi, J., et al.
(author)
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Parameter estimation for compact binary coalescence signals with the first generation gravitational-wave detector network
- 2013
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In: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 88:6
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Journal article (peer-reviewed)abstract
- Compact binary systems with neutron stars or black holes are one of the most promising sources for ground-based gravitational-wave detectors. Gravitational radiation encodes rich information about source physics; thus parameter estimation and model selection are crucial analysis steps for any detection candidate events. Detailed models of the anticipated waveforms enable inference on several parameters, such as component masses, spins, sky location and distance, that are essential for new astrophysical studies of these sources. However, accurate measurements of these parameters and discrimination of models describing the underlying physics are complicated by artifacts in the data, uncertainties in the waveform models and in the calibration of the detectors. Here we report such measurements on a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a "blind injection'' where the signal was not initially revealed to the collaboration. We exemplify the ability to extract information about the source physics on signals that cover the neutron-star and black-hole binary parameter space over the component mass range 1M(circle dot)-25M(circle dot) and the full range of spin parameters. The cases reported in this study provide a snapshot of the status of parameter estimation in preparation for the operation of advanced detectors.
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| 2. |
- Abadie, J., et al.
(author)
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All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run
- 2012
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In: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:12
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Journal article (peer-reviewed)abstract
- We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration less than or similar to 1 s over the frequency band 64-5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGO-Virgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitational-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc(3) for sample populations of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range similar to 5 x 10(-22) Hz(-1/2) to similar to 1 x 10(-20) Hz(-1/2). The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors.
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| 3. |
- Abadie, J., et al.
(author)
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First low-latency LIGO plus Virgo search for binary inspirals and their electromagnetic counterparts
- 2012
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 541
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Journal article (peer-reviewed)abstract
- Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was conducted. The resulting triggers were sent to electromagnetic observatories for followup. We describe the generation and processing of the low-latency gravitational-wave triggers. The results of the electromagnetic image analysis will be described elsewhere. Results. Over the course of the science run, three gravitational-wave triggers passed all of the low-latency selection cuts. Of these, one was followed up by several of our observational partners. Analysis of the gravitational-wave data leads to an estimated false alarm rate of once every 6.4 days, falling far short of the requirement for a detection based solely on gravitational-wave data.
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| 4. |
- Abadie, J., et al.
(author)
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Search for Gravitational Waves Associated with Gamma-Ray Bursts during LIGO Science Run 6 and Virgo Science Runs 2 and 3
- 2012
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In: Astrophysical Journal. - 0004-637X. ; 760:1
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Journal article (peer-reviewed)abstract
- We present the results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole, and a search for generic, unmodeled gravitational-wave bursts. We find no evidence for gravitational-wave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitational-wave emission energy of 10(-2) M-circle dot c(2) at 150 Hz, with a median limit of 17 Mpc. For short-hard GRBs we place exclusion distances on binary neutron star and neutron-star-black-hole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc, respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.
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| 5. |
- Abadie, J., et al.
(author)
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Search for gravitational waves from intermediate mass binary black holes
- 2012
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In: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:10
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Journal article (peer-reviewed)abstract
- We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100-450 M-circle dot and with the component mass ratios between 1: and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 M-circle dot, for nonspinning sources, the rate density upper limit is 0.13 per Mpc(3) per Myr at the 90% confidence level.
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| 6. |
- Abadie, J., et al.
(author)
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Upper limits on a stochastic gravitational-wave background using LIGO and Virgo interferometers at 600-1000 Hz
- 2012
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In: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:12
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Journal article (peer-reviewed)abstract
- A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600-1000 Hz, we obtained a 95% upper limit on the amplitude of Omega(GW)(f) = Omega(3)(f/900 Hz)(3), of Omega(3) < 0.32, assuming a value of the Hubble parameter of h(100) = 0.71. These new limits are a factor of seven better than the previous best in this frequency band.
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| 7. |
- Karpenka, Natalia V., 1986-, et al.
(author)
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A simple and robust method for automated photometric classification of supernovae using neural networks
- 2013
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 429:2, s. 1278-1285
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Journal article (peer-reviewed)abstract
- A method is presented for automated photometric classification of supernovae (SNe) as Type Ia or non-Ia. A two-step approach is adopted in which (i) the SN light curve flux measurements in each observing filter are fitted separately to an analytical parametrized function that is sufficiently flexible to accommodate virtually all types of SNe and (ii) the fitted function parameters and their associated uncertainties, along with the number of flux measurements, the maximum-likelihood value of the fit and Bayesian evidence for the model, are used as the input feature vector to a classification neural network that outputs the probability that the SN under consideration is of Type Ia. The method is trained and tested using data released following the Supernova Photometric Classification Challenge (SNPCC), consisting of light curves for 20 895 SNe in total. We consider several random divisions of the data into training and testing sets: for instance, for our sample D-1 (D-4), a total of 10 (40) per cent of the data are involved in training the algorithm and the remainder used for blind testing of the resulting classifier; we make no selection cuts. Assigning a canonical threshold probability of p(th) = 0.5 on the network output to class an SN as Type Ia, for the sample D-1 (D-4) we obtain a completeness of 0.78 (0.82), purity of 0.77 (0.82) and SNPCC figure of merit of 0.41 (0.50). Including the SN host-galaxy redshift and its uncertainty as additional inputs to the classification network results in a modest 5-10 per cent increase in these values. We find that the quality of the classification does not vary significantly with SN redshift. Moreover, our probabilistic classification method allows one to calculate the expected completeness, purity and figure of merit (or other measures of classification quality) as a function of the threshold probability p(th), without knowing the true classes of the SNe in the testing sample, as is the case in the classification of real SNe data. The method may thus be improved further by optimizing p(th) and can easily be extended to divide non-Ia SNe into their different classes.
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| 8. |
- Karpenka, Natallia V., 1986-, et al.
(author)
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Bayesian constraints on dark matter halo properties using gravitationally lensed supernovae
- 2013
-
In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 433:4, s. 2693-2705
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Journal article (peer-reviewed)abstract
- A hierarchical Bayesian method is applied to the analysis of Type Ia supernovae (SNIa) observations to constrain the properties of the dark matter haloes of galaxies along the SNIa lines of sight via their gravitational lensing effect. The full joint posterior distribution of the dark matter halo parameters is explored using the nested sampling algorithm MultiNest, which also efficiently calculates the Bayesian evidence, thereby facilitating robust model comparison. We first demonstrate the capabilities of the method by applying it to realistic simulated SNIa data, based on the real 3-year data release from the Supernova Legacy Survey (SNLS3). Assuming typical values for the parameters in a truncated singular isothermal sphere (SIS) halo model, we find that a catalogue analogous to the existing SNLS3 data set is typically incapable of detecting the lensing signal, but a catalogue containing approximately three times as many SNIa can produce robust and accurate parameter constraints and lead to a clear preference for the SIS halo model over a model that assumes no lensing. In the analysis of the real SNLS3 data, contrary to previous studies, we obtain only a very marginal detection of a lensing signal and weak constraints on the halo parameters for the truncated SIS model, although these constraints are tighter than those typically obtained from equivalent simulated SNIa data sets. This difference is driven by a preferred value of eta approximate to 1 in the assumed scaling law sigma proportional to L-eta between velocity dispersion and luminosity, which is somewhat higher than the canonical values of eta = 1/4 and eta = 1/3 for early and late-type galaxies, respectively.
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| 9. |
- Karpenka, Natalia V., et al.
(author)
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Testing the mutual consistency of different supernovae surveys
- 2015
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 449:3, s. 2405-2412
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Journal article (peer-reviewed)abstract
- It is now common practice to constrain cosmological parameters using supernovae (SNe) catalogues constructed from several different surveys. Before performing such a joint analysis, however, one should check that parameter constraints derived from the individual SNe surveys that make up the catalogue are mutually consistent. We describe a statistically-robust mutual consistency test, which we calibrate using simulations, and apply it to each pairwise combination of the large surveys making up, respectively, the UNION2 catalogue and the very recent JLA (joint light-curve analysis) compilation by Betoule et al. We find no inconsistencies in the latter case, but conclusive evidence for inconsistency between some survey pairs in the UNION2 catalogue.
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| 10. |
- March, M. C., et al.
(author)
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Comparison of cosmological parameter inference methods applied to supernovae light curves fitted with salt-II
- 2014
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 437:4, s. 3298-3311
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Journal article (peer-reviewed)abstract
- We present a comparison of two methods for cosmological parameter inference from Type Ia supernovae (SNeIa) light curves fitted with the salt-ii technique, in which we treat the statistical errors but not the systematic errors. The standard chi(2) methodology and the recently proposed SNeIa Bayesian hierarchical method (SNBHM) are each applied to identical sets of simulations based on the 3-yr data release from the Supernova Legacy Survey (SNLS3), and also data from the Sloan Digital Sky Survey, the low-redshift sample and the Hubble Space Telescope, assuming a concordance Lambda cold dark matter cosmology. For both methods, we find that the recovered values of the cosmological parameters, and the global nuisance parameters controlling the stretch and colour corrections to the supernovae light curves, suffer from small biases. The magnitude of the biases is similar in both cases, with the SNBHM yielding slightly more accurate results for cosmological parameters when applied to just the SNLS3 single survey data sets. Most notably, in this case, the biases in the recovered matter density (m,0) are in opposite directions for the two methods. For any given realization of the SNLS3-type data, this can result in a similar to 2 Sigma discrepancy in the estimated value of (m,0) between the two methods, which we find to be the case for real SNLS3 data. As more higher and lower redshift SNIa samples are included, however, the cosmological parameter estimates of the two methods converge.
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