SELECTED PROJECTS FROM THE PAST
EGRG has been a member of the LSC since 2007. This page gives an overview on a few selected projects from the past carried out by various EGRG members.
To see the list of currently ongoing projects EGRG members work on, please click on the project links in the sidebar to the left.
DATA ANALYSIS PROJECTS
Towards searching for gravitational-wave signals from eccentric binary black holes
Gondan, Raffai, and Frei, in coordination with the Burst and EBBH Working Groups
We investigate the astrophysically allowed ranges of parameters of eccentric binary black holes (EBBHs) in galactic nucleus and in globular cluster environments [D11]. These parameters include initial eccentricity, masses, and initial pericenter distance. The aim of this project is to identify the maximum volume and the source distributions within the parameter space that need to be covered with a search for EBBH signals. We take into account how much the ranges of parameters are bound by the fact that stable binaries must form in presence of many other black holes in the environment, which could disrupt the formation process. This effect has so far remained uninvestigated in previous EBBH studies.
We also study the simulated waveforms of EBBH signals, with the main focus of modelling the arrival times and durations of GW-bursts in the repeated burst phase of the EBBH waveform evolution [D11]. The aim of this study is to explore the possibility of reducing the parameter space to be covered in a search process for EBBH repeated bursts with a simplified but still sufficiently accurate model of burst timing data. With such a model, we could directly apply techniques such as the one introduced in Murphy+ 2013 [R39] developed to aim repeated bursts from a given astrophysical source.
We have developed an algorithm that can automatically extract the arrival times and durations of repeated bursts from EBBH waveforms. Using an extensive set of waveforms produced by EBBH waveform simulators, we perform statistical studies on the peak durations of the individual burst events, and on their distances in time. As the different waveform simulators produce robust timing data for the repeated bursts, we have an opportunity to develop a search technique that is practically independent from the exact EBBH models.
Cartoon of the formation process of an eccentric binary black hole
Searching for repeated gravitational-wave transients
Raffai in coordination with the Burst Working Group
While working as a postdoc member of the LIGO group at Columbia University, New York, Peter Raffai participated in the development of a detection method that aims to find any type of repeated gravitational-wave burst (GW-burst) signals emitted by the same astrophysical source. Examples for such astrophysical sources include soft gamma-repeaters (SGRs) and eccentric binary black holes (EBBHs).
The detection method was introduced in a paper published in Physical Review D [R39]. The paper also introduced a data quality veto method, and presented sensitivity test results with simulated S5 data, where, as an example, the simulated repeated GW-bursts were associated with SGR quasi-periodic oscillations.
Members of EGRG have also investigated the possibility of applying the search technique in future searches for SGR and EBBH repeated bursts. As part of this project, we have produced a software tool [T9] that projects simulated signals to the output data stream of any chosen existing (or even hypothetical) GW-detectors. The tool uses the physical parameters of a simulated GW-source and the GPS time of arrival of the signal, and calculates the h(t) output for any given GW-detector, using time-dependent antenna factors (that are necessary to be taken to account for these long GW-transients). The tool also calculates the antenna factor corrected projections of individual bursts, providing an opportunity to optimize the number of such bursts taken to account in the search process in terms of maximizing signal-to-noise ratio.
Detector background with and without a simulated data quality step [R39]
An X-ray source catalog for the LIGO X-ray Follow-up Program
Raffai and Frei, in coordination with the Burst and EM Follow-up Working Groups
We have constructed a catalog of ~750 000 X-ray sources that are also possible candidates for producing gravitational waves in the LIGO-Virgo band (XGWC Catalog) [D7]. The XGWC catalog is based on public data resources, such as the Master X-ray Catalog of the HEASARC Data Archive and the Gravitational Wave Galaxy Catalog. The purpose of this work is to support X-ray background studies for joint observations (such as in the LIGO Swift Follow-up project), using current and future X-ray telescopes and GW detectors.
We have also developed a software tool that is capable of browsing among the catalog elements using various search parameters [T8]. The tool allows source background investigations within proposed observational tiles of an X-ray telescope. An on-line public version of the catalog and the search tool is available HERE. The XGWC and the on-line search tool has already been used in background studies for Swift observations triggered by LIGO-Virgo GW events [L35], doing prompt searches for known X-ray sources within the reconstructed Swift tiles.
Sky distribution of the XGWC X-ray sources and GWGC galaxies.
Developing a new software for spinning waveform generation
Tapai and Gergely, in coordination with the CBC and Spinning Working Groups
The formerly applied algorithm used for spinning waveform generation, called SpinTaylor, generates precessing spinning waveforms using the fourth order Runge-Kutta method with adaptive stepsize. We have developed a similar program, called SpinQuadTaylor, which includes all spin effects (spin-orbit, spin-spin, self-spin) and the mass quadrupolar effects up to 2PN in the phase. Thus it is more accurate, and also faster than SpinTaylor, and has a Doxygen generated documentation, such that any potential users can have access to the information about the functions and the parameters it uses. The software produces inspiral waveforms both for equal and IMR masses, and they can be trusted also for mass ratios <0.1.
Spinning waveforms generated by the SpinQuadTaylor algorithm.
Developing the new waveform family of Spin Dominated Waveforms
Tapai and Gergely, in coordination with the CBC and Spinning Working Groups
We have developed a new waveform family for gravitational waves emitted by binary black holes with the larger component having a mass of 30 to 140 times the mass of the smaller one. In this mass ratio regime the spin of the larger component dominates over the orbital angular momentum of the system throughout the inspiral. Hence the name spin-dominated waveform (SDW) has been introduced [R38].
We started to develop an SDW generating code, to be implemented in LALsimulation. The time scale of SDW being in the sensitive band of Advanced LIGO is several seconds, hence it qualifies as a long GW-transient. We propose to study whether the STAMP algorithm [R34] is an effective detection method when searching for SDWs.
Time scale of SDWs in the aLIGO band, as function of total mass and mass ratio [R38]
DETECTOR CHARACTERIZATION PROJECTS
First sound at GEO600
Frei, Gelencsér, Szeifert, and Szokoly, in coordination with the DetChar Working Group and the GEO600 Collaboration
Although the critical components of the detectors are protected by vacuum against vibrations due to sound waves, several others are not. In March 2009 we successfully demonstrated at the GEO600 gravitational-wave (GW) detector site in Hannover, Germany, that sound waves generated outside the detector chamber indeed show up in the GW detector output [D1][D8]. This so called "coupling" between the acoustic and gravitational-wave data was later confirmed by other experiments at GEO600 and at LIGO Hanford. In our experiments, we used an off-the-shelf subwoofer to generate sound waves, and monitored the GW data output. The same patterns due to our injections not only showed up systematically in the GW channel, but also in the data of two independent microphone devices we used. Although our measurements only proved that acoustic coupling exists for the GEO600 detector, since other detectors have very similar design, we concluded that similar results on coupling are suspected for other detectors as well.
Our group members taking measurements at the GEO600 detector site.
Spectral densities of the GW detector output during sound injections, relative to the background data, where there was no injection. The effect of the 42 Hz (solid) and 137 Hz (dashed) injections are clearly visible in the spectra, as well as some harmonics.
Studying infrasound effects in GW detectors
Szeifert, Raffai, and Gelencsér, in coordination with the DetChar Working Group
In 2009 we have carried out a series of experiments at the GEO600 detector site in Hannover, Germany, that proved that acoustic excitations show up in the gravitational-wave detector output. As a theoretical follow-up of these experiments, we have studied the effects of sound waves on ground-based interferometric gravitational-wave detectors [D8]. In particular, we put an emphasis on low-frequency sound, based on the fact that at infrasonic frequencies (a) the environmental noise background in higher due to a huge number of sources and larger propagation distances; (b) possible coupling mechanisms have remained uninvestigated in this frequency region; (c) the low-frequency acoustic noise has not been monitored at the detector sites; (d) there are recent theoretical models predicting noise sources (e.g. airplane sonic booms) directly affecting the interferometer test masses, causing an increased level of the noise background (see Creighton, T., 2008.).
Therefore we have overviewed all infrasound sources possibly affecting the detectors, and developed a general model of acoustic coupling to detector components. Theoretically, the vacuum in current and advanced detectors suppresses the direct effect of sound waves below the seismic noise level, however several detector components are outside the vacuum and can directly be affected. Also, for future instruments, where the seismic noise level is reduced, there is a chance that sound waves remain the major limiting factor of noise reduction at low frequencies. Third generation instruments will be even more affected due to the fact that underground tunnels, where they are proposed to be built, could amplify sound waves at infrasound frequencies. We have designed a complex system of infrsound detectors, that could be used to continuously monitor the on-site acoustic noise background, while being protected against the effects of local wind noise. We propose to carry out on-site measurements, experimentally investigating the coupling mechanisms, and characterizing the on-site acoustic noise.
Theoretically modeled transmission curves of sound pressure waves affecting the interferometer test masses in a low-pressure gaseous medium. The transmission curves are given for various sound frequencies and for a propagation distance of 1 m.
Development of an infrasound microphone
Gelencsér, Szeifert, Raffai, Szokoly, and Marton, in coordination with the DetChar Working Group
We have developed an infrasound microphone device to monitor on-site low-frequency acoustic noise around gravitational-wave detectors. Although LIGO is expected to detect gravitational waves at higher frequencies, possible coupling of infrasound noise to the h(t) channel so far has not been studied. The basic concept of our device is quite simple: ambient pressure is measured relative to a pressure reference inside a small volume. The heart of the system is a completely self-designed very sensitive differential pressure sensor [D1] with resolution better than 1 mPa. We tested our infrasonic microphone with a commercial subwoofer for sound generation to measure the noise background and its effects to the h(t) channel at the GEO600 detector site. We propose to use multiple IS microphones for detector characterization as part of the Physical Environment Monitoring (PEM) system of currently operating and future detectors [D8].
The heart of our infrasound microphone: the differential pressure sensor.
Exploring acoustic coupling at LIGO Hanford
Gelencsér, Raffai, and Szeifert, in coordination with the DetChar Working Group
To explore and study the possible infrasound coupling to the gravitational-wave data channel, one of our infrasound microphones was installed in the LIGO Hanford Observatory in August 2010. Since then, it has been continuously gathering data, monitoring the on-site acoustic background. We have developed a complex software tool capable extracting data from various data channels, and looking for correlations between them and the microphone data. Correlations are currently being studied at various times and for various environmental conditions. We propose to model and report any correlations found between the chosen channels, in order to understand the underlying mechanisms responsible for the acoustic coupling we demonstrated previously at the GEO600 site.
Our self-designed infrasound microphone at the LIGO Hanford Observatory.
Next generation Physical Environment Monitoring
Szokoly, Szeifert, Gelencsér, Molnár, Imrek, Marton, in coordination with the DetChar Working Group
We have developed an alternative data collecting system for the Physical Environment Monitoring (PEM) system [D1]. It is based on several different equipments such as DAC boxes, ADC boxes, and universal data collecting and data transfering embedded computer nodes. The new design is fully modular, thus, any number of sensors can be easily integrated without any major effort. This system gives us freedom to use any kind of sensor with both digital and analog output, or any actuator or servo. The nodes are connected via 100Base-TX ethernet to the central data collecting sytem. The nodes are commercial embedded low power boards (NGW100) running linux. The sensors, DAC boxes, and ADC boxes are connected with RS-485 bus to a node. In this system the analog voltages are converted to digital values as near as possible to the source, thus, the effect of EM and RF noise is minimized beacause the data travels in digital form. In the future, we propose to implement our board to the existing PEM system of the LIGO detectors to provide support for the environment monitoring during the Advanced LIGO era.
Daughterboard for the NWG100: provides 8 analog or 4 differential analog input channels and an RS-485 interface.
A spectrum comparison tool for PEM
Szeifert, Gelencsér, and Raffai, in coordination with the DetChar Working Group
We have developed a detector characterization software tool, which is capable of comparing the spectra of the same Physical Environment Monitoring (PEM) channel or any other LIGO data at different times. This allows an easy and practical way for tracking changes in the data, focusing on noise peaks that might appear, changes in correlation properties or shifts in the data DC level. The tool is proposed to be included among the standard functions of the LIGO Data Viewer software package, but an LVC protected on-line version of the tool is also available HERE, where one can use it directly by downloading data with given parameters from the Network Data Server (Sigg, D 1999, LIGO Document T990124-D). The on-line tool is suitable for providing prompt information on spectral changes to science monitors or operators working at different detector sites. We are also planning to use our software tool for monitoring the spectral changes in the data of our self-developed infrasound microphone device.
Amplitude spectral densities of a PEM data channel at different times.
|(c) Eötvös Gravity Research Group 2007|