Gravitational-wave (GW) observations by a network of ground-based laser interferometric detectors allow us to probe the nature of GW polarizations. This would be an interesting test of general ...relativity, since general relativity predicts only two polarization modes while there are theories of gravity that predict up to six polarization modes. The ability of GW observations to probe the nature of polarizations is limited by the available number of linearly independent detectors in the network. (To extract all polarization modes, there should be at least as many detectors as the polarization modes.) Strong gravitational lensing of GWs offers a possibility to significantly increase the effective number of detectors in the network. Due to strong lensing (e.g., by galaxies), multiple copies of the same signal can be observed with time delays of several minutes to weeks. Owing to the rotation of the earth, observation of the multiple copies of the same GW signal would allow the network to measure different combinations of the same polarizations. This effectively multiplies the number of detectors in the network. Focusing on strongly lensed signals from binary black hole mergers that produce two observable "images," using Bayesian model selection and assuming simple polarization models, we show that our ability to distinguish between polarization models is significantly improved.
We search for signatures of gravitational lensing in the binary black hole events detected by Advanced LIGO and Virgo during their first two observational runs. In particular, we look for three ...effects: (1) evidence of lensing magnification in the individual signals due to galaxy lenses, (2) evidence of multiple images due to strong lensing by galaxies, and (3) evidence of wave optics effects due to point-mass lens. We find no compelling evidence of any of these signatures in the observed gravitational wave signals. However, as the sensitivities of gravitational wave detectors improve in the future, detecting lensed events may become quite likely.
In this critical compilation, all experimental data on the spectrum of neutral carbon known to us were methodically evaluated and supplemented by parametric calculations with Cowan's codes. The ...sources of experimental data vary from laboratory to astrophysical objects, and employ different instrumentations, from classical grating and Fourier transform spectrometers to precise laser spectroscopy setups and various other modern techniques. This comprehensive evaluation provides accurate atomic data on energy levels and wavelengths (observed and Ritz) with their estimated uncertainties, as well as a uniform description of the observed line intensities. In total, 412 previously known energy levels were optimized with the help of 1221 selected best-observed lines participating in 1365 transitions in the wavelength region 750 -609.14 m. The list of recommended energy levels is extended by including 21 additional levels found through quantum-defect extrapolations or parametric calculations with Cowan's codes. In addition, 737 possibly observable transitions are predicted. Critically evaluated transition probabilities for 1616 lines are provided, of which 241 are new. With accurate energy levels obtained, combined with additional observed data on high Rydberg states, the ionization limit was determined to be 90820.348(9) cm−1 or 11.2602880(11) eV, in fair agreement with the previously recommended value, but more accurate.
Abstract
All available experimental data on the spectrum of singly ionized carbon have been critically analyzed. Measurement uncertainties of all published studies have been reassessed. The scope of ...observational data includes laboratory emission spectra of arcs, sparks, electrodeless discharges, and hollow cathode lamps recorded with grating and Fourier transform spectrometers, laboratory photoabsorption spectra, and emission spectra of planetary nebulae. The total number of observed spectral lines included in this compilation is 597. These lines participate in 972 transitions. From this list of identified transitions, we have derived a set of 414 energy levels, which are optimized using a least-squares fitting procedure. The identifications are supported by parametric calculations with Cowan’s codes. The existing tables of critically evaluated transition probabilities have been extended with our newly calculated data. The ionization energy has been derived from the newly optimized energy levels with improved precision. Data on the isotope shifts and hyperfine structure have also been compiled.
ABSTRACT
Gravitational waves, like light, can be gravitationally lensed by massive astrophysical objects such as galaxies and galaxy clusters. Strong gravitational-wave lensing, forecasted at a ...reasonable rate in ground-based gravitational-wave detectors such as Advanced LIGO, Advanced Virgo, and KAGRA, produces multiple images separated in time by minutes to months. These images appear as repeated events in the detectors: gravitational-wave pairs, triplets, or quadruplets with identical frequency evolution originating from the same sky location. To search for these images, we need to, in principle, analyse all viable combinations of individual events present in the gravitational-wave catalogues. An increasingly pressing problem is that the number of candidate pairs that we need to analyse grows rapidly with the increasing number of single-event detections. At design sensitivity, one may have as many as $\mathcal {O}(10^5)$ event pairs to consider. To meet the ever-increasing computational requirements, we develop a fast and precise Bayesian methodology to analyse strongly lensed event pairs, enabling future searches. The methodology works by replacing the prior used in the analysis of one strongly lensed gravitational-wave image by the posterior of another image; the computation is then further sped up by a pre-computed lookup table. We demonstrate how the methodology can be applied to any number of lensed images, enabling fast studies of strongly lensed quadruplets.
ABSTRACT
Owing to the forecasted improved sensitivity of ground-based gravitational-wave detectors, new research avenues will become accessible. This is the case for gravitational-wave strong ...lensing, predicted with a non-negligible observation rate in the coming years. However, because one needs to investigate all the event pairs in the data, searches for strongly lensed gravitational waves are often computationally heavy, and one faces high false-alarm rates. In this paper, we present upgrades made to the golum software, making it more reliable while increasing its speed by re-casting the look-up table, imposing a sample control, and implementing symmetric runs on the two lensed images. We show how the recovered posteriors have improved coverage of the parameter space and how we increase the pipeline’s stability. Finally, we show the results obtained by performing a joint analysis of all the events reported until the GWTC-3 catalogue, finding similar conclusions to the ones presented in the literature.
Abstract
A spectral investigation of triply ionized gold (Au
iv
) has been carried out in the wavelength region of 500–2106 Å. The gold spectra were photographed at the National Institute of ...Standards and Technology, USA, on a 10.7 m normal incidence vacuum spectrograph (NIVS) using a sliding spark source as well as on a 3 m NIVS at the Antigonish laboratory in Canada with a triggered spark source. Our analysis is theoretically supported by the pseudorelativistic Hartree–Fock (HFR) formalism with a superposition of configuration interactions implemented in Cowan's suite of codes. Radiative transition parameters are also calculated using the HFR+CPOL (core polarization effects) model and the multiconfiguration Dirac–Hartree–Fock approach, and their comparisons are used to evaluate the transition rate data. All the previously reported levels of the 5
d
8
, 5
d
7
6
s
, and 5
d
7
6
p
configurations are confirmed, except one, and three are newly established. The missing
1
S
0
level of 5
d
8
is now established at 55,277.8 cm
−1
. A total of 981 observed lines (E1 type), classified to 1031 transitions, including 133 newly identified, enabled us to optimize 139 energy levels. Several astrophysically important transitions, forbidden (M1- and E2-type) lines of 5
d
8
and 5
d
7
6
s
, are provided with their Ritz wavelengths and radiative parameters. A critically evaluated set of energy levels, observed and Ritz wavelengths along with their uncertainties, transition rates, and uniformly scaled intensities of Au
iv
lines have been presented. Also, large-scale atomic data to compute the opacity of Au
iv
in the kilonova ejecta have been supplemented in this work.
A global network of advanced interferometric gravitational wave detectors is expected to be on-line soon. Coherent observation of gravitational waves from a distant compact binary coalescence with a ...network of interferometers located in different continents gives crucial information about the source, such as its location and polarization. In this paper we compare different multidetector network detection statistics for compact binary coalescence searches. In maximum likelihood ratio based detection approaches, the likelihood ratio is optimized to obtain the best model parameters, and the best likelihood ratio value is used as a statistic to make decisions regarding the presence of signals. However, an alternative Bayesian approach involves the marginalization of the likelihood ratio over the parameters and obtains the average likelihood ratio test. We obtain an analytical expression for the Bayesian statistic using the two effective synthetic data streams for targeted searches of nonspinning compact binary systems with an uninformative prior on the parameters. Simulations are carried out to test the validity of the approximation and compare the detection performance with the maximum likelihood ratio and the “hybrid” statistic. We observe that the hybrid statistic gives comparable or better performance with respect to the Bayesian statistic.
In this article, we revisit the coherent gravitational wave search problem of compact binary coalescences with multidetector network consisting of advanced interferometers like LIGO-Virgo. Based on ...the loss of the optimal multidetector signal-to-noise ratio (SNR), we construct a hybrid statistic as a best of maximum-likelihood-ratio (MLR) statistic tuned for face-on and face-off binaries. The statistical properties of the hybrid statistic is studied. The performance of this hybrid statistic is compared with that of the coherent MLR statistic for generic inclination angles. Owing to the single synthetic data stream, the hybrid statistic gives few false alarms compared to the multidetector MLR statistic and small fractional loss in the optimum SNR for a large range of binary inclinations. We demonstrate that, for a LIGO-Virgo network and binary inclination epsilon<70degrees and epsilon>110degrees, the hybrid statistic captures more than 98% of the network optimum matched filter SNR with a low false alarm rate. The Monte Carlo exercise with two distributions of incoming inclination angles-namely, Ucosepsilon and a more realistic distribution proposed by B.F. Schutz Classical Quantum Gravity 28, 125023 (2011)-are performed with the hybrid statistic and give approximately 5% and 7% higher detection probabilities, respectively, compared to the two stream multidetector MLR statistic for a fixed false alarm probability of 10 super(-5).
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