278 research outputs found
Tiling strategies for optical follow-up of gravitational wave triggers by wide field of view telescopes
Binary neutron stars are among the most promising candidates for joint
gravitational-wave and electromagnetic astronomy. The goal of this work is to
investigate the strategy of using gravitational wave sky-localizations for
binary neutron star systems, to search for electromagnetic counterparts using
wide field of view optical telescopes. We examine various strategies of
scanning the gravitational wave sky-localizations on the mock 2015-16
gravitational-wave events. We propose an optimal tiling-strategy that would
ensure the most economical coverage of the gravitational wave sky-localization,
while keeping in mind the realistic constrains of transient optical astronomy.
Our analysis reveals that the proposed tiling strategy improves the
sky-localization coverage over naive contour-covering method. The improvement
is more significant for observations conducted using larger field of view
telescopes, or for observations conducted over smaller confidence interval of
gravitational wave sky-localization probability distribution. Next, we
investigate the performance of the tiling strategy for telescope arrays and
compare their performance against monolithic giant field of view telescopes. We
observed that distributing the field of view of the telescopes into arrays of
multiple telescopes significantly improves the coverage efficiency by as much
as 50% over a single large FOV telescope in 2016 localizations while scanning
around 100 sq. degrees. Finally, we studied the ability of optical counterpart
detection by various types of telescopes. In Our analysis for a range of wide
field-of-view telescopes we found improvement in detection upon sacrificing
coverage of localization in order to achieve greater observation depth for very
large field-of-view - small aperture telescopes, especially if the intrinsic
brightness of the optical counterparts are weak.Comment: Accepted for publication in A&A. 10 pages, 10 figure
Tiling strategies for optical follow-up of gravitational-wave triggers by telescopes with a wide field of view
Aims. Binary neutron stars are among the most promising candidates for joint gravitational-wave and electromagnetic astronomy. The goal of this work is to investigate various observing strategies that telescopes with wide field of view might incorporate while searching for electromagnetic counterparts of gravitational-wave triggers.
Methods. We examined various strategies of scanning the gravitational-wave sky localizations on the mock 2015−16 gravitational-wave events. First, we studied the performance of the sky coverage using a naive tiling system that completely covers a given confidence interval contour using a fixed grid. Then we propose the ranked-tiling strategy where we sample the localization in discrete two-dimensional intervals that are equivalent to the telescope’s field of view and rank them based on their sample localizations. We then introduce an optimization of the grid by iterative sliding of the tiles. Next, we conducted tests for all the methods on a large sample of sky localizations that are expected in the first two years of operation of the Laser interferometer Gravitational-wave Observatory (LIGO) and Virgo detectors. We investigated the performance of the ranked-tiling strategy for telescope arrays and compared their performance against monolithic telescopes with a giant field of view. Finally, we studied the ability of optical counterpart detection by various types of telescopes.
Results. Our analysis reveals that the ranked-tiling strategy improves the localization coverage over the contour-covering method. The improvement is more significant for telescopes with larger fields of view. We also find that while optimizing the position of the tiles significantly improves the coverage compared to contour-covering tiles. For ranked-tiles the same procedure leads to negligible improvement in the coverage of the sky localizations. We observed that distributing the field of view of the telescopes into arrays of multiple telescopes significantly improves the coverage efficiency, by as much as 50% over a single telescope with a large field of view in 2016 localizations while scanning ~100 deg2. Finally, through analyzing a range telescopes with wide field of view, we discovered that counterpart detection can be improved by sacrificing coverage of localization in order to achieve a greater observation depth for telescopes with very large field of view and small aperture, especially if the intrinsic brightness of the optical counterparts is weak
A Machine Learning Based Source Property Inference for Compact Binary Mergers
The detection of the binary neutron star (BNS) merger, GW170817, was the
first success story of multi-messenger observations of compact binary mergers.
The inferred merger rate along with the increased sensitivity of the
ground-based gravitational-wave (GW) network in the present LIGO/Virgo, and
future LIGO/Virgo/KAGRA observing runs, strongly hints at detection of binaries
which could potentially have an electromagnetic (EM) counterpart. A rapid
assessment of properties that could lead to a counterpart is essential to aid
time-sensitive follow-up operations, especially robotic telescopes. At minimum,
the possibility of counterparts require a neutron star (NS). Also, the tidal
disruption physics is important to determine the remnant matter post merger,
the dynamics of which could result in the counterparts. The main challenge,
however, is that the binary system parameters such as masses and spins
estimated from the real time, GW template-based searches are often dominated by
statistical and systematic errors. Here, we present an approach that uses
supervised machine-learning to mitigate such selection effects to report
possibility of counterparts based on presence of a NS component, and presence
of remnant matter post merger in real time.Comment: accepted in Ap
First Search for Nontensorial Gravitational Waves from Known Pulsars
We present results from the first directed search for nontensorial gravitational waves. While general relativity allows for tensorial (plus and cross) modes only, a generic metric theory may, in principle, predict waves with up to six different polarizations. This analysis is sensitive to continuous signals of scalar, vector, or tensor polarizations, and does not rely on any specific theory of gravity. After searching data from the first observation run of the advanced LIGO detectors for signals at twice the rotational frequency of 200 known pulsars, we find no evidence of gravitational waves of any polarization. We report the first upper limits for scalar and vector strains, finding values comparable in magnitude to previously published limits for tensor strain. Our results may be translated into constraints on specific alternative theories of gravity
Search for Gravitational Waves from Compact Binary Coalescence In LIGO and Virgo Data from S5 and VSR1
We report the results of the first search for gravitational waves from compact binary coalescence using data from the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo detectors. Five months of data were collected during the concurrent S5 (LIGO) and VSR1 (Virgo) science runs. The search focused on signals from binary mergers with a total mass between 2 and 35 M. No gravitational waves are identified. The cumulative 90%-confidence upper limits on the rate of compact binary coalescence are calculated for nonspinning binary neutron stars, black hole-neutron star systems, and binary black holes to be 8.7×10−3 yr−1L−1 10 , 2.2×10−3 yr−1L−1 10 , and 4.4×10−4 yr−1L−1 10 respectively, where L10 is 1010 times the blue solar luminosity. These upper limits are compared with astrophysical expectations
Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory
The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the GeV-EeV energy range using the Antares, IceCube, and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within ± 500 s around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We further carried out an extended search in the direction of the source for high-energy neutrinos within the 14 day period following the merger, but found no evidence of emission. We used these results to probe dissipation mechanisms in relativistic outflows driven by the binary neutron star merger. The non-detection is consistent with model predictions of short GRBs observed at a large off-axis angle
First Search for Gravitational Waves from the Youngest Known Neutron Star
We present a search for periodic gravitational waves from the neutron star in the supernova remnant Cassiopeia A. The search coherently analyzes data in a 12 day interval taken from the fifth science run of the Laser Interferometer Gravitational-Wave Observatory. It searches gravitational-wave frequencies from 100 to 300 Hz and covers a wide range of first and second frequency derivatives appropriate for the age of the remnant and for different spin-down mechanisms. No gravitational-wave signal was detected. Within the range of search frequencies, we set 95% confidence upper limits of (0.7-1.2) × 10 -24 on the intrinsic gravitational-wave strain, (0.4-4) × 10-4 on the equatorial ellipticity of the neutron star, and 0.005-0.14 on the amplitude of r-mode oscillations of the neutron star. These direct upper limits beat indirect limits derived from energy conservation and enter the range of theoretical predictions involving crystalline exotic matter or runaway rmodes. This paper is also the first gravitational-wave search to present upper limits on the r-mode amplitude
Systematic effects from black hole-neutron star waveform model uncertainties on the neutron star equation of state
We identify various contributors of systematic effects in the measurement of
the neutron star (NS) tidal deformability and quantify their magnitude for
several types of neutron star - black hole (NSBH) binaries. Gravitational waves
from NSBH mergers contain information about the components' masses and spins as
well as the NS equation of state. Extracting this information requires
comparison of the signal in noisy detector data with theoretical templates
derived from some combination of post-Newtonian (PN) approximants, effective
one-body (EOB) models and %analytic fits to numerical relativity (NR)
simulations. The accuracy of these templates is limited by errors in the NR
simulations, by the approximate nature of the PN/EOB waveforms, and by the
hybridization procedure used to combine them. In this paper, we estimate the
impact of these errors by constructing and comparing a set of PN-NR hybrid
waveforms, for the first time with NR waveforms from two different codes,
namely, SpEC and SACRA, for such systems. We then attempt to recover the
parameters of the binary using two non-precessing template approximants. We
find that systematic errors are too large for tidal effects to be accurately
characterized for any realistic NS equation of state model. We conclude that
NSBH waveform models must be significantly improved if they are to be useful
for the extraction of NS equation of state information or even for
distinguishing NSBH systems from binary black holes
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