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Target-based optimization of advanced gravitational-wave detector network operations

Journal Paper
Szölgyén, Á., Dálya, G., Gondán, L., and Raffai, P.
Classical and Quantum Gravity, Vol. 34, p. 7
Publication year: 2017

We introduce two novel time-dependent figures of merit for both online and offline optimizations of advanced gravitational-wave (GW) detector network operations with respect to (i) detecting continuous signals from known source locations and (ii) detecting GWs of neutron star binary coalescences from known local galaxies, which thereby have the highest potential for electromagnetic counterpart detection. For each of these scientific goals, we characterize an N-detector network, and all its (N  −  1)-detector subnetworks, to identify subnetworks and individual detectors (key contributors) that contribute the most to achieving the scientific goal. Our results show that aLIGO-Hanford is expected to be the key contributor in 2017 to the goal of detecting GWs from the Crab pulsar within the network of LIGO and Virgo detectors. For the same time period and for the same network, both LIGO detectors are key contributors to the goal of detecting GWs from the Vela pulsar, as well as to detecting signals from 10 high interest pulsars. Key contributors to detecting continuous GWs from the Galactic Center can only be identified for finite time intervals within each sidereal day with either the 3-detector network of the LIGO and Virgo detectors in 2017, or the 4-detector network of the LIGO, Virgo, and KAGRA detectors in 2019–2020. Characterization of the LIGO-Virgo detectors with respect to goal (ii) identified the two LIGO detectors as key contributors. Additionally, for all analyses, we identify time periods within a day when lock losses or scheduled service operations could result with the least amount of signal-to-noise or transient detection probability loss for a detector network.

Parameter Estimation for Gravitational-wave Bursts with the BayesWave Pipeline

Journal Paper
Bécsy, B., Raffai, P., Cornish, N. J., et al. (+6 authors)
The Astrophysical Journal, Vol. 839, Number 1
Publication year: 2017

We provide a comprehensive multi-aspect study on the performance of a pipeline used by the LIGO-Virgo Collaboration for estimating parameters of gravitational-wave bursts. We add simulated signals with four different morphologies (sine-Gaussians, Gaussians, white-noise bursts, and binary black hole signals) to simulated noise samples representing noise of the two Advanced LIGO detectors during their first observing run. We recover them with the BayesWave (BW) pipeline to study its accuracy in sky localization, waveform reconstruction, and estimation of model-independent waveform parameters. BW localizes sources with a level of accuracy comparable for all four morphologies, with the median separation of actual and estimated sky locations ranging from 25.1 to 30.3. This is a reasonable accuracy in the two-detector case, and is comparable to accuracies of other localization methods studied previously. As BW reconstructs generic transient signals with sine-Gaussian wavelets, it is unsurprising that BW performs the best in reconstructing sine-Gaussian and Gaussian waveforms. BW’s accuracy in waveform reconstruction increases steeply with network signal-to-noise ratio (SNRnet), reaching a 85% and 95% match between the reconstructed and actual waveform below SNRnet20 and SNRnet50, respectively, for all morphologies. BW’s accuracy in estimating central moments of waveforms is only limited by statistical errors in the frequency domain, and is affected by systematic errors too in the time domain as BW cannot reconstruct low-amplitude parts of signals overwhelmed by noise. The figures of merit we introduce can be used in future characterizations of parameter estimation pipelines.

A Statistical Method for Detecting Gravitational Recoils of Supermassive Black Holes in Active Galactic Nuclei

Conference Paper
Raffai, P., Bécsy, B., Haiman, Z., Frei, Z.
New Frontiers in Black Hole Astrophysics, Proceedings of the International Astronomical Union, IAU Symposium, Volume 324, pp. 227-230
Publication year: 2017

We propose an observational test for gravitationally recoiling supermassive black holes in active galactic nuclei, based on a positive correlation between the velocities of black holes relative to their host galaxies, |Δv|, and their obscuring dust column densities, Σdust, both measured along the line of sight. Our findings using a set of toy models implemented to a Monte Carlo simulation imply that models of the galactic centre and of recoil dynamics can be tested by future observations of the potential Σdust-|Δv| correlation. We have also found that the fraction of obscured quasars decreases with |Δv|, for which the predicted trend can be compared to the observed fraction of type II quasars, and can further test combinations of models we may implement.

Interferométerekkel a gravitációs hullámok nyomában

Outreach Paper
Bécsy Bence, Dálya Gergely, Raffai Péter
Természet Világa, Vol. 147., Issue 3.
Publication year: 2016

Einstein 1915-ben közölte korszakalkotó elméletét, az általános relativitáselméletet. Ezt a gravitáció újszerű leírását adó elméletet az elmúlt egy évszázad alatt számtalan alkalommal tesztelték különböző kísérletekkel, és mindmáig helyesnek bizonyult. Az elmélet utolsónak bizonyított olyan jóslata, amit maga Einstein tett, az a gravitációs hullámok létezése. A gravitációs hullámok első közvetlen detektálása éppen száz évvel az általános relativitáselmélet megszületése után, 2015 szeptemberében történt, amelyet 2016. február 11-én jelentett be sajtótájékoztatóján a felfedezést jegyző LIGO és VIRGO kollaboráció. Jelen cikkben betekintést nyújtunk a gravitációs hullámok világába.

GW150914: először hallottuk az Univerzum zenéjét

Outreach Paper
Dálya Gergely, Bécsy Bence, Raffai Péter
Meteor, Vol. XLVI., Issue 3. (480.)
Publication year: 2016

A LIGO-Virgo nemzetközi kollaboráció 2015. február 11-én tartott sajtótájékoztatóján bejelentette, hogy sikerült gravitációs hullámokat detektálniuk. Ebben a cikkben áttekintjük, hogy hogyan történt a felfedezés, mit is detektáltak pontosan, és hogy mi ennek a jelentősége.

All-sky search for long-duration gravitational wave transients with initial LIGO

LSC Paper
Abbott, B. P., … Raffai, P., et al. (+934 authors)
Physical Review D, Vol. 93, Issue 4, id. 042005
Publication year: 2016

We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4 ×1 0-5 and 9.4 ×1 0-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves.

A statistical method to search for recoiling supermassive black holes in active galactic nuclei

Journal Paper
Raffai, P., Haiman, Z., and Frei Z.
Monthly Notices of the Royal Astronomical Society, Vol. 455, p. 484
Publication year: 2016

We propose an observational test for gravitationally recoiling supermassive black holes (BHs) in active galactic nuclei, based on a correlation between the velocities of BHs relative to their host galaxies, |Δv|, and their obscuring dust column densities, Σdust (both measured along the line of sight). We use toy models for the distribution of recoil velocities, BH trajectories, and the geometry of obscuring dust tori in galactic centres, to simulate 2.5 × 105 random observations of recoiling quasars. BHs with recoil velocities comparable to the escape velocity from the galactic centre remain bound to the nucleus, and do not fully settle back to the centre of the torus due to dynamical friction in a typical quasar lifetime. We find that |Δv| and Σdust for these BHs are positively correlated. For obscured (Σdust > 0) and for partially obscured (0 < Σdust ≲ 2.3 g m-2) quasars with |Δv| ≥ 45 km s-1, the sample correlation coefficient between log10(|Δv|) and Σdust is r45 = 0.28 ± 0.02 and r45 = 0.13 ± 0.02, respectively. Allowing for random ± 100 km s– 1 errors in |Δv| unrelated to the recoil dilutes the correlation for the partially obscured quasars to r45 = 0.026 ± 0.004 measured between |Δv| and Σdust. A random sample of ≳ 3500 obscured quasars with |Δv| ≥ 45 km s-1would allow rejection of the no-correlation hypothesis with 3σ significance 95 per cent of the time. Finally, we find that the fraction of obscured quasars, {F_obs} (|Δv|), decreases with |Δv| from {F_obs} (<10 km s-1) ≳ 0.8 to {F_obs} (>103 km s-1) ≲ 0.4. This predicted trend can be compared to the observed fraction of type II quasars, and can further test combinations of recoil, trajectory, and dust torus models.

Global Optimization for Future Gravitational Wave Detectors' Sites

Journal Paper
Hu, Y., Raffai, P., Gondán, L., et al. (+5 authors)
Classical and Quantum Gravity, Vol. 32, p. 105010
Publication year: 2015

We consider the optimal site selection of future generations of gravitational wave (GW) detectors. Previously, Raffai et al optimized a two-detector network with a combined figure of merit (FoM). This optimization was extended to networks with more than two detectors in a limited way by first fixing the parameters of all other component detectors. In this work we now present a more general optimization that allows the locations of all detectors to be simultaneously chosen. We follow the definition of Raffai et al on the metric that defines the suitability of a certain detector network. Given the locations of the component detectors in the network, we compute a measure of the network’s ability to distinguish the polarization, constrain the sky localization and reconstruct the parameters of a GW source. We further define the ‘flexibility index’ for a possible site location, by counting the number of multi-detector networks with a sufficiently high FoM that include that site location. We confirm the conclusion of Raffai et al, that in terms of the flexibility index as defined in this work, Australia hosts the best candidate site to build a future generation GW detector. This conclusion is valid for either a three-detector network or a five-detector network. For a three-detector network, site locations in Northern Europe display a comparable flexibility index to sites in Australia. However, for a five-detector network, Australia is found to be a clearly better candidate than any other location.

Concepts and research for future detectors

Conference Paper
Acernese F., …, Raffai P., et al.
General Relativity and Gravitation, Vol. 46, p. 1700
Publication year: 2014

Technologies, design aspects and recent progresses for future gravitational wave (GW) detectors are mentioned in this summary of the C4 session of the Amaldi 10 conference.

Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts

LSC Paper
Aasi, J., … Raffai, P., et al. (+875 authors)
Physical Review D, Vol. 88, Issue 12, p. 122004
Publication year: 2013

Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (˜10-1000s) GW emission associated with the accretion disk of a collapsed star or with its protoneutron star remnant. Using data from LIGO’s fifth science run, and GRB triggers from the Swift experiment, we perform a search for unmodeled long-lived GW transients. Finding no evidence of GW emission, we place 90% confidence-level upper limits on the GW fluence at Earth from long GRBs for three waveforms inspired by a model of GWs from accretion disk instabilities. These limits range from F<3.5ergscm-2 to F<1200ergscm-2, depending on the GRB and on the model, allowing us to probe optimistic scenarios of GW production out to distances as far as ≈33Mpc. Advanced detectors are expected to achieve strain sensitivities 10× better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs.

Optimal networks of future gravitational-wave telescopes

Journal Paper
Raffai, P., Gondán, L., Heng, I. S., et al. (+4 authors)
Classical and Quantum Gravity, Vol. 30, p. 155004
Publication year: 2013

We aim to find the optimal site locations for a hypothetical network of 1-3 triangular gravitational-wave telescopes. We define the following N-telescope figures of merit (FoMs) and construct three corresponding metrics: (a) capability of reconstructing the signal polarization; (b) accuracy in source localization; and (c) accuracy in reconstructing the parameters of a standard binary source. We also define a combined metric that takes into account the three FoMs with practically equal weight. After constructing a geomap of possible telescope sites, we give the optimal 2-telescope networks for the four FoMs separately in example cases where the location of the first telescope has been predetermined. We found that based on the combined metric, placing the first telescope to Australia provides the most options for optimal site selection when extending the network with a second instrument. We suggest geographical regions where a potential second and third telescope could be placed to get optimal network performance in terms of our FoMs. Additionally, we use a similar approach to find the optimal location and orientation for the proposed LIGO-India detector within a five-detector network with Advanced LIGO (Hanford), Advanced LIGO (Livingston), Advanced Virgo, and KAGRA. We found that the FoMs do not change greatly in sites within India, though the network can suffer a significant loss in reconstructing signal polarizations if the orientation angle of an L-shaped LIGO-India is not set to the optimal value of ~58.2°( + k × 90°) (measured counterclockwise from East to the bisector of the arms).

Detecting long-duration narrow-band gravitational wave transients associated with soft gamma repeater quasiperiodic oscillations

Journal Paper
Murphy, D., Tse, M., Raffai, P., et al. (+6 authors)
Physical Review D, Vol. 87, Issue 10, p. 103008
Publication year: 2013

We have performed an in-depth concept study of a gravitational wave data analysis method which targets repeated long quasimonochromatic transients (triggers) from cosmic sources. The algorithm concept can be applied to multitrigger data sets in which the detector-source orientation and the statistical properties of the data stream change with time, and does not require the assumption that the data is Gaussian. Reconstructing or limiting the energetics of potential gravitational wave emissions associated with quasiperiodic oscillations observed in the x-ray lightcurve tails of soft gamma repeater flares might be an interesting endeavor of the future. Therefore we chose this in a simplified form to illustrate the flow, capabilities, and performance of the method. We investigate performance aspects of a multitrigger based data analysis approach by using O(100s) long stretches of mock data in coincidence with the times of observed quasiperiodic oscillations, and by using the known sky location of the source. We analytically derive the probability density function of the background distribution and compare to the results obtained by applying the concept to simulated Gaussian noise, as well as off-source playground data collected by the 4-km Hanford detector during LIGO’s fifth science run (S5). We show that the transient glitch rejection and adaptive differential energy comparison methods we apply succeed in rejecting outliers in the fifth science run background data. Finally, we discuss how to extend the method to a network containing multiple detectors, and as an example, tune the method to maximize sensitivity to soft gamma repeater 1806-20 flare times.

The Advanced LIGO Timing System Timing Comparator/Radio Frequency Counter Module

LIGO Document
Raffai, P., Belopolski, I., Countryman, S., et al. (+2 authors)
LIGO Document T1200331
Publication year: 2012

Swift Follow-up Observations of Candidate Gravitational-wave Transient Events

LSC Paper
Evans, P. A., … Raffai, P., et al. (+814 authors)
The Astrophysical Journal Supplement, Vol. 203, Issue 2, p. 14
Publication year: 2012

We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors (within less than 10 minutes) and their candidate sky locations were observed by the Swift observatory (within 12 hr). Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a “blind injection challenge.” With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime, multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.

Multimessenger Sources of Gravitational Waves and High-energy Neutrinos: Science Reach and Analysis Method

Conference Paper
Baret, B., I. Bartos, B. Bouhou, E. Chassande-Mottin, A. Corsi, I. Di Palma, C. Donzaud, M. Drago, C. Finley, G. Jones, S. Klimenko, A. Kouchner, S. Márka, Z. Márka, L. Moscoso, M. A. Papa, T. Pradier, G. Prodi, P. Raffai, V. Re, J. Rollins, F. Salemi, P. Sutton, M. Tse, V. Van Elewyck and G. Vedovato
Journal of Physics: Conference Series, Vol. 363, Issue 1, p. 012022
Publication year: 2012

Sources of gravitational waves are often expected to be observable through several messengers, such as gamma-rays, X-rays, optical, radio, and/or neutrino emission. The simultaneous observation of electromagnetic or neutrino emission with a gravitational-wave signal could be a crucial aspect for the first direct detection of gravitational waves. Furthermore, combining gravitational waves with electromagnetic and neutrino observations will enable the extraction of scientific insight that was hidden from us before. We discuss the method that enables the joint search with the LIGO-Virgo-IceCube-ANTARES global network, as well as its methodology, science reach, and outlook for the next generation of gravitational-wave detectors.

Multimessenger science reach and analysis method for common sources of gravitational waves and high-energy neutrinos

Journal Paper
Baret, B., Bartos, … Raffai, P., et al. (+23 authors)
Physical Review D, Vol. 35, Issue 10, p. 103004
Publication year: 2012

We present the baseline multimessenger analysis method for the joint observations of gravitational waves (GW) and high-energy neutrinos (HEN), together with a detailed analysis of the expected science reach of the joint search. The analysis method combines data from GW and HEN detectors, and uses the blue-luminosity-weighted distribution of galaxies. We derive expected GW+HEN source rate upper limits for a wide range of source parameters covering several emission models. Using published sensitivities of externally triggered searches, we derive joint upper limit estimates both for the ongoing analysis with the initial LIGO-Virgo GW detectors with the partial IceCube detector (22 strings) HEN detector and for projected results to advanced LIGO-Virgo detectors with the completed IceCube (86 strings). We discuss the constraints these upper limits impose on some existing GW+HEN emission models.

Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

LSC Paper
Abadie, J., … Raffai, P., et al. (+813 authors)
Astronomy & Astrophysics, Vol. 539, p. A124
Publication year: 2012

Aims: A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations.
Methods: During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline’s ability to reconstruct source positions correctly.
Results: For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.

Application of interferometric gravitational-wave detectors in astrophysics and gravity research

Thesis
Raffai, P.
(in Hungarian), Ph.D. thesis, Eötvös Loránd University, Budapest
Publication year: 2012

Opportunity to Test non-Newtonian Gravity Using Interferometric Sensors with Dynamic Gravity Field Generators

Journal Paper
Raffai, P., Szeifert, G., Matone, L., et al. (+5 authors)
Physical Review D, Vol. 84, Issue 8, p. 082002
Publication year: 2011

We present an experimental opportunity for the future to measure possible violations to Newton’s 1/r2 law in the 0.1-10 m range using dynamic gravity field generators (DFG) and taking advantage of the exceptional sensitivity of modern interferometric techniques. The placement of a DFG in proximity to one of the interferometer’s suspended test masses generates a change in the local gravitational field that can be measured at a high signal to noise ratio. The use of multiple DFGs in a null-experiment configuration allows us to test composition-independent non-Newtonian gravity significantly beyond the present limits. Advanced and third-generation gravitational-wave detectors are representing the state-of-the-art in interferometric distance measurement today, therefore, we illustrate the method through their sensitivity to emphasize the possible scientific reach. Nevertheless, it is expected that due to the technical details of gravitational-wave detectors, DFGs shall likely require dedicated custom-configured interferometry. However, the sensitivity measure we derive is a solid baseline indicating that it is feasible to consider probing orders of magnitude into the pristine parameter well beyond the present experimental limits significantly cutting into the theoretical parameter space.

Long gravitational-wave transients and associated detection strategies for a network of terrestrial interferometers

Journal Paper
Thrane, E., Kandhasamy, S., … Raffai, P., et al. (+10 authors)
Physical Review D, Vol. 83, Issue 8, p. 083004
Publication year: 2011

Searches for gravitational waves (GWs) traditionally focus on persistent sources (e.g., pulsars or the stochastic background) or on transients sources (e.g., compact binary inspirals or core-collapse supernovae), which last for time scales of milliseconds to seconds. We explore the possibility of long GW transients with unknown waveforms lasting from many seconds to weeks. We propose a novel analysis technique to bridge the gap between short O(s) “burst” analyses and persistent stochastic analyses. Our technique utilizes frequency-time maps of GW strain cross power between two spatially separated terrestrial GW detectors. The application of our cross power statistic to searches for GW transients is framed as a pattern recognition problem, and we discuss several pattern-recognition techniques. We demonstrate these techniques by recovering simulated GW signals in simulated detector noise. We also recover environmental noise artifacts, thereby demonstrating a novel technique for the identification of such artifacts in GW interferometers. We compare the efficiency of this framework to other techniques such as matched filtering.

Bounding the time delay between high-energy neutrinos and gravitational-wave transients from gamma-ray bursts

Journal Paper
Baret, B., Bartos, I., … Raffai, P., et al. (+16 authors)
Astroparticle Physics, Vol. 35, Issue 1, p. 1-7
Publication year: 2011

We derive a conservative coincidence time window for joint searches of gravitational-wave (GW) transients and high-energy neutrinos (HENs, with energies ≳100 GeV), emitted by gamma-ray bursts (GRBs). The last are among the most interesting astrophysical sources for coincident detections with current and near-future detectors. We take into account a broad range of emission mechanisms. We take the upper limit of GRB durations as the 95% quantile of the T90‘s of GRBs observed by BATSE, obtaining a GRB duration upper limit of ˜150 s. Using published results on high-energy (>100 MeV) photon light curves for 8 GRBs detected by Fermi LAT, we verify that most high-energy photons are expected to be observed within the first ˜150 s of the GRB. Taking into account the breakout-time of the relativistic jet produced by the central engine, we allow GW and HEN emission to begin up to 100 s before the onset of observable gamma photon production. Using published precursor time differences, we calculate a time upper bound for precursor activity, obtaining that 95% of precursors occur within ˜250 s prior to the onset of the GRB. Taking the above different processes into account, we arrive at a time window of tHEN – tGW ∈ [-500 s, +500 s]. Considering the above processes, an upper bound can also be determined for the expected time window of GW and/or HEN signals coincident with a detected GRB, tGW – tGRB ≈ tHEN– tGRB ∈ [-350 s, +150 s]. These upper bounds can be used to limit the coincidence time window in multimessenger searches, as well as aiding the interpretation of the times of arrival of measured signals.

User’s manual for the Infrasonic Microphone System developed by the Eötvös Gravity Research Group

LIGO Document
Gelencsér, G., Szeifert, G., Raffai, P., et al. (+3 authors)
LIGO Document E1000282
Publication year: 2010

This manual describes the usage of the Infrasonic Microphone System (IsMS), that was developed by the Eötvös Gravity Research Group (EGRG) at Eötvös Loránd University, Budapest, Hungary.

Search for gravitational-wave bursts associated with gamma-ray bursts using data from LIGO Science Run 5 and Virgo Science Run 1

LSC Paper
Abbott, B. P., … Raffai, P., et al. (+664 authors)
The Astrophysical Journal, Vol. 715, p. 1438
Publication year: 2010

We present the results of a search for gravitational-wave bursts (GWBs) associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO-Virgo sites. We find no evidence for GWB signals associated with this sample of GRBs. Using simulated short-duration (<1 s) waveforms, we set upper limits on the amplitude of gravitational waves associated with each GRB. We also place lower bounds on the distance to each GRB under the assumption of a fixed energy emission in gravitational waves, with a median limit of D ~12 Mpc(E iso GW/0.01 M sun c 2)1/2 for emission at frequencies around 150 Hz, where the LIGO-Virgo detector network has best sensitivity. We present astrophysical interpretations and implications of these results, and prospects for corresponding searches during future LIGO-Virgo runs.

Recovering a spinning inspiralling compact binary waveform immersed in LIGO-like noise with spinning templates

Conference Paper
L. Veréb, Z. Keresztes, P. Raffai, S. Mészáros, L. Á. Gergely
Journal of Physics: Conference Series, Vol. 228, p. 012003
Publication year: 2010

We investigate the recovery chances of highly spinning waveforms immersed in LIGO S5-like noise by performing a matched filtering with 106 randomly chosen spinning waveforms generated with the LAL package. While the masses of the compact binary are reasonably well recovered (slightly overestimated), the same does not hold true for the spins. We show the best fit matches both in the time-domain and the frequency-domain. These encompass some of the spinning characteristics of the signal, but far less than what would be required to identify the astrophysical parameters of the system. An improvement of the matching method is necessary, though may be difficult due to the noisy signal.

LUMIN Expert Shifter Manual

LIGO Document
Raffai, P.
LIGO Document M1000224
Publication year: 2010

The LUMIN Expert shifts started on 11th August 2010. This document provides an overview on the Expert tasks during the shift, useful links, contact info, and hints.

Compact binary waveform recovery from the cross-correlated data of two detectors by matched filtering with spinning templates

Conference Paper
L. Veréb, Z. Keresztes, P. Raffai, Zs. Udvari, M. Tápai, L. Á. Gergely
Journal of Physics: Conference Series, Vol. 243, p. 012008
Publication year: 2010

We investigate whether the recovery chances of highly spinning waveforms by matched filtering with randomly chosen spinning waveforms generated with the LAL package are improved by a cross-correlation of the simulated output of the L1 and H1 LIGO detectors. We find that a properly defined correlated overlap improves the mass estimates and enhaces the recovery of spin angles.

An X-ray source catalog for joint gravitational wave and X-ray observations

LIGO Document
Raffai, P., Handbauer, P.
LIGO Document T1000305
Publication year: 2010

We present a catalog of X-ray radiation sources that are also possible candidates for producing gravitational waves. The purpose of this work is to support X-ray background studies for joint observations using current and future X-ray telescopes (in particular the Swift telescope) and gravitational wave detectors, such as LIGO and Virgo.

Concept Study of Yukawa-like Potential Tests Using Dynamic Gravity Gradients with Interferometric Gravitational Wave Detectors

Conference Paper
P. Raffai, S. Márka, L. Matone and Z. Márka
Proceedings of the Eleventh Marcel Grossmann Meeting on General Relativity, edited by H. Kleinert, R.T. Jantzen and R. Ruffini, World Scientific, Singapore, p. 2382-2385
Publication year: 2008

We present a technique to measure possible violations to Newton’s 1/r2 law using a pair of matched Dynamic gravity Field Generators (DFGs) in a null-experiment and taking advantage of the exceptional sensitivity of modern suspended mass interferometric gravitational wave detectors. The correct placement of the DFGs, i.e. rotating symmetrical two-body masses, in proximity to one of the interferometer’s suspended test masses, allows future tests of composition independent non-Newtonian gravity beyond the present limits. We give our calculation and simulation results in context ofYukawa-like potentials in the 0.5 – 10 meter range.

Inverted Pendulum as Low Frequency Pre-Isolation for Advanced Gravitational Wave Detectors

Journal Paper
Takamori, A., Raffai, P., Márka, S., et al. (+9 authors)
Nuclear Instruments & Methods in Physics Research A, Vol. 582, Issue 2, p. 683-692
Publication year: 2007

We have developed advanced seismic attenuation systems for Gravitational Wave (GW) detectors. The design consists of an Inverted Pendulum (IP) holding stages of Geometrical Anti-Spring Filters (GASF) and pendula, which isolate the test mass suspension from ground noise. The ultra-low-frequency IP suppresses the horizontal seismic noise, while the GASF suppresses the vertical ground vibrations. The three legs of the IP are supported by cylindrical maraging steel flexural joints. The IP can be tuned to very low frequencies by carefully adjusting its load. As a best result, we have achieved an ultra low, ~12 mHz pendulum frequency for the system prototype made for Advanced LIGO (Laser Interferometer Gravitational Wave Observatory). The measured quality factor, Q, of this IP, ranging from Q~2500 (at 0.45 Hz) to Q~2 (at 12 mHz), is compatible with structural damping, and is proportional to the square of the pendulum frequency. Tunable counterweights allow for precise center-of-percussion tuning to achieve the required attenuation up to the first leg internal resonance (~60 Hz for advanced LIGO prototype). All measurements are in good agreement with our analytical models. We therefore expect good attenuation in the low-frequency region, from ~0.1 to ~50 Hz, covering the micro-seismic peak. The extremely soft IP requires minimal control force, which simplifies any needed actuation.

How to find long narrow-band gravitational wave transients with unknown frequency evolution?

Journal Paper
Raffai, P., Frei, Z., Márka, Z., et al. (+1 author)
Classical and Quantum Gravity, Vol. 24, p. S457-S468
Publication year: 2007

We present two general methods, the so-called Locust and the generalized Hough algorithm, to search for narrow-band signals of moderate frequency evolution and limited duration in datastreams of gravitational wave detectors. Some models of long gamma-ray bursts (e.g. van Putten et al 2004 Phys. Rev. D 69 044007) predict narrow-band gravitational wave burst signals of limited duration emitted during the gamma-ray burst event. These types of signals give rise to curling traces of local maxima in the time frequency space that can be recovered via image processing methods (Locust and Hough). Tests of the algorithms in the context of the van Putten model were carried out using injected simulated signals into Gaussian white noise and also into LIGO-like data. The Locust algorithm has the relative advantage of having higher speed and better general sensitivity; however, the generalized Hough algorithm is more tolerant of trace discontinuities. A combination of the two algorithms increases search robustness and sensitivity at the price of execution speed.

Benefits of Artificially Generated Gravity Gradients for Interferometric Gravitational Wave Detectors

Journal Paper
Matone, L., Raffai, P., Márka, S., et al. (+5 authors)
Classical and Quantum Gravity, Vol. 24, p. 2217-2229
Publication year: 2007

We present an approach to experimentally evaluate gravity gradient noise, a potentially limiting noise source in advanced interferometric gravitational wave (GW) detectors. In addition, the method can be used to provide sub-percent calibration in phase and amplitude of modern interferometric GW detectors. Knowledge of calibration to such certainties shall enhance the scientific output of the instruments in case of an eventual detection of GWs. The method relies on a rotating symmetrical two-body mass, a Dynamic gravity Field Generator (DFG). The placement of the DFG in the proximity of one of the interferometer’s suspended test masses generates a change in the local gravitational field detectable with current interferometric GW detectors.

Searching for quasi-monochromatic gravitational-wave signals in time-frequency space

Thesis
Raffai, P.
diploma thesis, Eötvös Loránd University, Budapest
Publication year: 2006

The diploma thesis is in Hungarian.

Gravitációs hullámok kutatása

Outreach Paper
Raffai Péter, Bartos Imre
Középiskolai Matematikai és Fizikai Lapok, 2006. május
Publication year: 2006

Az elektromágneses mérések legígéretesebb kiegészítője, s ezzel a jövő asztrofizikájának legfontosabb, mindezidáig kiaknázatlan információszerzési lehetősége a gravitációs kölcsönhatás kísérleti vizsgálata lehet. Az einsteini általános relativitáselmélet ugyanis már évtizedekkel napjaink előtt megjósolta egy, az elektromágneses hullámokhoz hasonló, ám gravitációs kölcsönhatásból származtatható sugárzás létezését. Hasonlóan az EM-hullámokhoz, e gravitációs hullámok is nagy hatótávolságúak, ami biztosítja, hogy detektálásukkal távoli objektumok, vagy a korai Univerzum tulajdonságait is képesek legyünk feltérképezni. Jóllehet létezésük közvetett úton már bizonyított, direkt kimutatásuk a mai napig várat magára.