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Vladimir Dergachev

Publications and source records attributed to Vladimir Dergachev.

At least 19 recordsLinked to original sources
arXiv2025

Early release of low-frequency atlas of continuous gravitational waves

We present the public release of the low-frequency atlas of continuous gravitational waves, covering signals with frequencies from 20 Hz to 200 Hz and frequency derivatives from -5e-11 to 5e-11 Hz/s. Compared to the previous atlas releases, this version demonstrates significant improvements in sensitivity and sky resolution. In the most sensitive region even the worst-case upper limits on gravitational wave strain are below 1e-25. The atlas data is being released ahead of the completion of the full follow-up analysis.

gr-qc↗
arXiv2025

Expanded atlas of the sky in continuous gravitational waves

We present the full release of the atlas of continuous gravitational waves, covering frequencies from 20 Hz to 1700 Hz and spindowns from -5e-10 to 5e-10 Hz/s. Compared to the early atlas release, we have extended the frequency range and have performed follow-up on the outliers. Conducting continuous wave searches is computationally intensive and time-consuming. The atlas facilitates the execution of new searches with relatively minimal computing resources.

gr-qc↗
arXiv2024

Efficient representations of upper limits and confidence intervals for experimental data

Upper limits and confidence intervals are a convenient way to present experimental results. With modern experiments producing more and more data, it is often necessary to reduce the volume of the results for convenient distribution. A common approach is to take a maximum over a set of upper limits, which yields an upper limit valid for the entire set. This, however, can result in significant sensitivity loss, because we discard more constraining data. In this paper we introduce functional upper limits and confidence intervals that allow to summarize results with small relaxation of constraints. A toy example and an application to upper limits in all-sky continuous gravitational wave searches are worked out.

gr-qc↗
arXiv2024

Early release of the expanded atlas of the sky in continuous gravitational waves

We present the early release of the atlas of continuous gravitational waves covering frequencies from 20 Hz to 1500 Hz and spindowns from -5e-10 to 5e-10 Hz/s. Compared to the previous atlas release we have greatly expanded the parameter space, and we now also provide polarization-specific data - both for signal-to-noise ratios and for the upper limits. Continuous wave searches are computationally difficult and take a long time to complete. The atlas enables new searches to be performed using modest computing power. To allow new searches to start sooner, we are releasing this data early, before our followup stages have completed.

gr-qc↗
arXiv2023

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 gravitational wave amplitude upper limits, signal-to-noise ratios (SNR) and frequencies where the search measures the maximum SNR. The approximately top 1.5% of the atlas results are reanalyzed with a series of more sensitive searches with the purpose of finding high SNR long coherence signals from isolated neutron stars. However, these searches do not reveal the presence of such signals. 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. The Falcon pipeline computes loosely coherent power estimates to search data using a succession of coherence lengths. For this search we used 6 months of data, started with a 12 hour coherence length and progressed to 6 days. 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. These results are within an order of magnitude of the _minimum_ neutron star ellipticity of 1e-9 suggested in [33].

gr-qc↗
arXiv2021

Characterizing the sensitivity of isolated continuous gravitational wave searches to binary orbits

Broadband all-sky searches for continuous gravitational waves (CW) from isolated neutron stars typically yield a number of significant candidates that are discarded through hierarchical semi-coherent and coherent follow-up searches. However, these searches target purely isolated sources and do not take into account possible phase modulations to the signals due to companion objects in binary orbits. If the source object is in a binary orbit, the signal-to-noise ratio (SNR) of a signal will diminish due to the mismatch between the signal waveform and the template waveform used in the search. In this paper, we investigate the sensitivity of CW searches to signals from sources in binary systems over an exhaustive range of binary orbits. We use Monte-Carlo simulations to constrain the ranges of binary orbital parameters that leave a CW signal from a source in a binary orbit visible in a search for signals from an isolated source (isolated searches), and consequently tighten the parameter space explorable with dedicated searches for signals from sources in binary systems (binary searches).

gr-qc↗
arXiv2021

The 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.

gr-qc↗
arXiv2021

Results from high-frequency all-sky search for continuous gravitational waves from small-ellipticity sources

We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 1700-2000 Hz range from neutron stars with ellipticity of 1e-8. The search employs the Falcon analysis pipeline [citation 5] on LIGO O2 public data. Our results improve by a factor greater than 5 over [citation 11]. This is a huge leap forward: it takes an entirely new generation of gravitational wave detectors to achieve a 10-fold sensitivity increase over the previous generation [citation 12]. Within the probed frequency range and aside from the detected outliers, we can exclude neutron stars with ellipticity of 1e-8 within 65 pc of Earth. We set upper limits on the gravitational wave amplitude that hold even for worst-case signal parameters. New outliers are found, some of which we are unable to associate with any instrumental cause. If any were associated with a rotating neutron star, this would likely be the fastest neutron star today.

gr-qc↗
arXiv2020

Results from the first all-sky search for continuous gravitational waves from small-ellipticity sources

We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 500-1700 Hz range targeting neutron stars with ellipticity of 1e-8. The search is done on LIGO O2 data using the Falcon analysis pipeline. The results presented here double the sensitivity over any other result on the same data. The search is capable of detecting low ellipticity sources up to 170 pc. We establish strict upper limits which hold for worst-case signal parameters. We list outliers uncovered by the search, including several which we cannot associate with any known instrumental cause.

gr-qc↗
arXiv2020

Search for Continuous Gravitational Waves from the Central Compact Objects in Supernova Remnants Cassiopeia A, Vela Jr. and G347.3-0.5

We perform a sub-threshold follow-up search for continuous nearly-monochromatic gravitational waves from the central compact objects associated with the supernova remnants 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.

astro-ph.HE↗
arXiv2019

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.

gr-qc↗
arXiv2019

Sensitivity improvements in the search for periodic gravitational waves using O1 LIGO data

We demonstrate a breakthrough in the capabilities of robust, broad-parameter space searches for continuous gravitational waves. With a large scale search for continuous gravitational waves on the O1 LIGO data, we prove that our Falcon search achieves the sensitivity improvements expected from the use of a long coherence length, while maintaining the computational expense within manageable bounds. On this data we set the most constraining upper limits in the gravitational wave amplitude in the band 100-200 Hz. We provide full outlier lists and upper limits near 0-spindown band suitable for analysis of signals with small spindown such as boson condensates around black holes.

gr-qc↗
arXiv2019

Astrophysical science metrics for next-generation gravitational-wave detectors

The second generation of gravitational-wave detectors are being built and tuned all over the world. The detection of signals from binary black holes is beginning to fulfill the promise of gravitational-wave 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.

astro-ph.HE↗
arXiv2019

Loosely coherent search in LIGO O1 data for continuous gravitational waves from Terzan 5 and the galactic center

We report results of a search for continuous gravitational waves from a region covering the globular cluster Terzan 5 and the galactic center. Continuous gravitational waves are expected from fast-spinning, slightly non-axisymmetric isolated neutron stars as well as more exotic objects. The regions that we target are believed to be unusually abundant in neutron stars. We use a new loosely coherent search method that allows to reach unprecedented levels of sensitivity for this type of search. The search covers the frequency band 475-1500 Hz and frequency time derivatives in the range of [-3e-8, +1e-9] Hz/s, which is a parameter range not explored before with the depth reached by this search. As to be expected with only a few months of data from the same observing run, it is very difficult to make a confident detection of a continuous signal over such a large parameter space. A list of parameter space points that passed all the thresholds of this search is provided. We follow-up the most significant outlier on the newly released O2 data and cannot confirm it. We provide upper limits on the gravitational wave strength of signals as a function of signal frequency.

gr-qc↗
arXiv2019

Results from an Einstein@Home search for continuous gravitational waves from Cassiopeia A, Vela Jr. and G347.3

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 $[1/ {\sqrt{\textrm{Hz}}}]$ and 83 $[1/ {\sqrt{\textrm{Hz}}}]$, 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 $h_0^{90\%}\approx 10^{-25}$, probing ellipticity values for Vela Jr. as low as $3\times 10^{-8}$, assuming a distance of 200 pc.

gr-qc↗
arXiv2019

Efficient Estimation of Barycentered Relative Time Delays for Distant Gravitational Wave Sources

Accurate determination of gravitational wave source parameters relies on transforming between the source and detector frames. All-sky searches for continuous wave sources are computationally expensive, in part, because of barycentering transformation of time delays to a solar system frame. This expense is exacerbated by the complicated modulation induced in signal templates. We investigate approximations for determining time delays of signals received by a gravitational wave detector with respect to the solar system barycenter. A highly non-linear conventional computation is transformed into one that has a pure linear sum in its innermost loop. We discuss application of these results to determination of the maximal useful integration time of continuous wave searches.

astro-ph.IM↗
arXiv2019

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 all-sky searches over medium scale coherence lengths (3-300 hours).

astro-ph.IM↗