We introduce a 'loosely coherent' method for detection of continuous gravitational waves that bridges the gap between semi-coherent and purely coherent methods. Explicit control over accepted ...families of signals is used to increase the sensitivity of a power-based statistic while avoiding the high computational costs of conventional matched filters. Several examples as well as a prototype implementation are discussed.
We perform a sub-threshold follow-up search for continuous nearly monochromatic gravitational waves from the central compact objects associated with the supernova remnants (SNRs) Vela Jr., Cassiopeia ...A, and SNR G347.3−0.5. Across the three targets, we investigate the most promising 10,000 combinations of gravitational-wave frequency and frequency derivative values, based on the results from an Einstein@Home search of the LIGO O1 observing run data, dedicated to these objects. The selection threshold is set so that a signal could be confirmed using the newly released O2 run LIGO data. In order to achieve best sensitivity we perform two separate follow-up searches, on two distinct stretches of the O2 data. Only one candidate survives the first O2 follow-up investigation, associated with the central compact object in SNR G347.3−0.5, but it is not conclusively confirmed. In order to assess a possible astrophysical origin we use archival X-ray observations and search for amplitude modulations of a pulsed signal at the putative rotation frequency of the neutron star and its harmonics. This is the first extensive electromagnetic follow-up of a continuous gravitational-wave candidate performed to date. No significant associated signal is identified. New X-ray observations contemporaneous with the LIGO O3 run will enable a more sensitive search for an electromagnetic counterpart. A focused gravitational-wave search in O3 data based on the parameters provided here should be easily able to shed light on the nature of this outlier. Noise investigations on the LIGO instruments could also reveal the presence of a coherent contamination.
Abstract
We conduct an all-sky search for continuous gravitational waves in the LIGO O2 data from the Hanford and Livingston detectors. We search for nearly monochromatic signals with frequency ...20.0 Hz ≤
f
≤ 585.15 Hz and spin-down
Hz s
−1
. We deploy the search on the Einstein@Home volunteer-computing project and follow-up the waveforms associated with the most significant results with eight further search stages, reaching the best sensitivity ever achieved by an all-sky survey up to 500 Hz. Six of the inspected waveforms pass all the stages but they are all associated with hardware injections, which are fake signals simulated at the LIGO detector for validation purposes. We recover all these fake signals with consistent parameters. No other waveform survives, so we find no evidence of a continuous gravitational wave signal at the detectability level of our search. We constrain the
h
0
amplitude of continuous gravitational waves at the detector as a function of the signal frequency, in half-Hz bins. The most constraining upper limit at 163.0 Hz is
h
0
= 1.3 × 10
−25
, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 10
−7
closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models.
The Antarctic is a highly connected system with nonlinear interactions between the atmosphere, ocean, ice, and biota, as well as complex connections to the rest of the Earth system. Antarctica and ...the Southern Ocean make up the most important part of the Earth system. Antarctica is the coldest, driest, and most remote continent and is undergoing a variety of environmental changes in response to climate change, in particular modern warming, which is the subject of intense scientific debate. Almost all of Antarctica is located south of the Antarctic Circle (66°33′ S). The question remains as to whether the recent and accelerating warming trend is part of natural climate variability or the result of anthropogenic activities. We may not get an unambiguous answer if we do not decipher how climate processes changed in the distant past. Long-term trends (ups and downs) in continental ice deposits in the Antarctic region and in carbon dioxide content can be distinguished over the interval of approximately the last 500 Ma. Nearly 60–50 million years ago there was a long trend of decreasing carbon dioxide concentration, average temperature and lowering of the ocean level. Over the last million and hundreds of thousands of years, the history of the Earth has been characterized by alternating cycles of cold (glacial) and warm (interglacial) climatic fluctuations, which led to a number of large-scale environmental and atmospheric changes, in particular, the formation and melting of huge ice sheets, dramatic changes in global sea level, etc. This article examines long-term trends in climate change in various regions of Antarctica in the past, climate change since the end of the last ice age, and current climate change, and the relationship of these changes with the causes that give rise to them. The main attention is drawn to the changes in climatic characteristics during the Holocene and the features of changes in recent decades. The results we obtained are important for understanding past and future climate variability.
The second generation of gravitational-wave (GW) detectors are being built and tuned all over the world. The detection of signals from binary black holes is beginning to fulfil the promise of GW ...astronomy. In this work, we examine several possible configurations for third-generation laser interferometers in existing km-scale facilities. We propose a set of astrophysically motivated metrics to evaluate detector performance. We measure the impact of detector design choices against these metrics, providing a quantitative cost-benefit analyses of the resulting scientific payoffs.
The temperature of the ocean waters and the heat content of the active layer of the ocean, sea currents and ice, salinity, and the characteristics of the water column are climatically important ...parameters of the World Ocean, between which there is a relationship. The ocean is in constant interaction with the atmosphere and the Earth’s crust, which is manifested by the exchange of heat, moisture, and momentum. In turn, the atmosphere also influences the ocean, through the circulation of waters. Changes in the state of the continental ice and fluctuations in ocean levels lead to the key consequences of climate change in most regions of the world. The main global causes of the impact on climate should be noted: changes in the period of the Sun’s revolution, solar activity, including solar radiation, volcanic emissions, and the greenhouse effect of the planet. This article considers the roles of the three oceans (Arctic, Atlantic, and Pacific) connected with the Arctic region and the role of ocean currents in the process of interlatitudinal heat transfer. The results of the analysis of both long-term and short-term ocean surface temperature variability covering different time intervals from the end of the last glacial period to the present and the connection of these changes with the causes generating them are presented. It is concluded that there is significant natural climate variability in the Arctic region over the studied time interval.
The direct detection of continuous gravitational waves from pulsars is a much anticipated discovery in the emerging field of multimessenger gravitational wave (GW) astronomy. Because putative pulsar ...signals are exceedingly weak large amounts of data need to be integrated to achieve desired sensitivity. Contemporary searches use ingenious ad hoc methods to reduce computational complexity. In this paper we provide analytical expressions for the Fourier transform of realistic pulsar signals. This provides description of the manifold of pulsar signals in the Fourier domain, used by many search methods. We analyze the shape of the Fourier transform and provide explicit formulas for location and size of peaks resulting from stationary frequencies. We apply our formulas to analysis of recently identified outlier at 1891.76 Hz.
New research methods are being developed to get a broad picture of the temperature changes throughout the World Ocean. A permanent global network of oceanographic stations based on Argo profiling ...buoys was created about 20 years ago. The main purpose of Argo profiling buoys is to measure the vertical profiles of the water temperature and salinity as they rise from the depth of the ocean to the surface. A fundamentally new method to determine changes in the mean temperature in the ocean began to be developed in the early 2000s. It is based on the use of the elemental and isotopic ratios of Ar with N
2
and the heavy inert (noble) gases Kr and Xe with N
2
contained in ice cores captured from the atmosphere by air bubbles. The use of these new methods gives scientists unique opportunities for the continuous monitoring of the state of the World Ocean. The work focuses on estimates of ocean temperature changes based on the available direct, historical data and indirect, experimental data, as well as data obtained with the aforementioned new methods. The reconstructions of temperatures for different time intervals are analyzed, and reconstructions of the global surface temperatures and ocean temperatures after the retreat of the last ice age, which were obtained from model and indirect experimental data, are compared.
Rapidly rotating neutron stars are promising sources of continuous gravitational wave radiation for the LIGO and Virgo interferometers. The majority of neutron stars in our galaxy have not been ...identified with electromagnetic observations. All-sky searches for isolated neutron stars offer the potential to detect gravitational waves from these unidentified sources. The parameter space of these blind all-sky searches, which also cover a large range of frequencies and frequency derivatives, presents a significant computational challenge. Different methods have been designed to perform these searches within acceptable computational limits. Here we describe the first benchmark in a project to compare the search methods currently available for the detection of unknown isolated neutron stars. The five methods compared here are individually referred to as the PowerFlux, sky Hough, frequency Hough, Einstein@Home, and time domain F-statistic methods. We employ a mock data challenge to compare the ability of each search method to recover signals simulated assuming a standard signal model. We find similar performance among the four quick-look search methods, while the more computationally intensive search method, Einstein@Home, achieves up to a factor of two higher sensitivity. We find that the absence of a second derivative frequency in the search parameter space does not degrade search sensitivity for signals with physically plausible second derivative frequencies. We also report on the parameter estimation accuracy of each search method, and the stability of the sensitivity in frequency and frequency derivative and in the presence of detector noise.
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 1/Hz and 83 1/Hz, depending on the target and the frequency range. At the frequency of best strain sensitivity, near 172 Hz, we set 90% confidence upper limits on the gravitational wave intrinsic amplitude of h090%≈10−25, probing ellipticity values for Vela Jr. as low as 3×10−8, assuming a distance of 200 pc.
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