On blind searches for noise dominated signals: a loosely coherent approach

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

Loosely coherent searches for sets of well-modeled signals

We introduce a high-performance implementation of a loosely coherent statistic sensitive to signals spanning a finite-dimensional manifold in parameter space. Results from full scale simulations on Gaussian noise are discussed, as well as implications for future searches for continuous gravitational waves. We demonstrate an improvement of more than an order of magnitude in analysis speed over previously available algorithms. As searches for continuous gravitational waves are computationally limited, the large speedup results in gain in sensitivity

Loosely coherent searches for medium scale coherence lengths

The search for continuous gravitational waves demands computationally efficient algorithms that can handle highly non-linear parameter spaces. Loosely coherent algorithms establish upper limits and detect signals by analyzing families of templates as a single unit. We describe a new computationally efficient loosely coherent search intended for spotlight and all-sky searches over medium scale coherence lengths (20000-1000000 sec)

Search for continuous gravitational waves from small-ellipticity sources at low frequencies

We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 20-500 Hz range from neutron stars with ellipticity of 1e-8. This frequency region is particularly hard to probe because of the quadratic dependence of signal strength on frequency. The search employs the Falcon analysis pipeline on LIGO O2 public data. Compared to previous Falcon analyses the coherence length has been quadrupled, with a corresponding increase in sensitivity. This enables us to search for small ellipticity neutron stars in this low frequency region up to 44 pc away. The frequency derivative range is up to 3e-13 Hz/s easily accommodating sources with ellipticities of 1e-7 and a corresponding factor of 10 increase in reach. New outliers are found, many of which we are unable to associate with any instrumental cause

A frequency resolved atlas of the sky in continuous gravitational waves

We present the first atlas of the continuous gravitational wave sky, produced using LIGO O3a public data. For each 0.045 Hz frequency band and every point on the sky the atlas provides upper limits, signal-to-noise ratios (SNR) and frequencies where the search measures the maximum SNR. The results presented in the atlas are produced with the Falcon pipeline and cover nearly monochromatic gravitational wave signals in the 500-1000 Hz band, with up to +/-5e-11 Hz/s frequency derivative. Compared to the most sensitive results previously published (also produced with the Falcon pipeline) our upper limits are 50% more constraining. Neutron stars with ellipticity of 1e-8 can be detected up to 150 pc away, while allowing for a large fraction of the stars' energy to be lost through non-gravitational channels

Results from an extended Falcon all-sky survey for continuous gravitational waves

We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 200-600 Hz range and frequency derivative (spindown) from -1e-8 through 1.11e-9 Hz/s. Together with the results from [1], this search completes the all-sky survey for frequencies between 20 to 600 Hz on O1 data. It also demonstrates the scalability of our search on a parameter space 26 times larger than previously considered. The results presented here complement the LIGO O2 data results [2,3] with comparable when not better sensitivity and do not rely on data with irregularities in the noise-subtraction procedure. We establish strict upper limits which hold for worst-case signal parameters and dedicated upper limits for generic ~0 spindown signals, such as those expected from boson condensates around black holes

A chronology of the Scythian antiquities of Eurasia based on new archaeological and C-14 data

The paper is compares the chronology of the monuments of the Scythian epoch located in the east and west of the Eurasian steppe zone on the basis of both archaeological and radiocarbon data. The lists of C-14 dates for the monuments located in different parts of Eurasia are presented according to the periods of their existence. Generally, the C-14 dates are confirmed the archaeological point of view and allow us to compare the chronological position of the European and Asian Scythian monuments on the united C-14 time scale