Gravitational-wave Physics & Astronomy Workshop (GWPAW) Banner
GWPAW Workshop

Quick Links

What's New

January 31, 2011

Talks available for download

January 29, 2011

Poster Prizes Awarded

January 20, 2011

Poster Information

Scientific Program: Wednesday | Thursday | Friday | Saturday

Wednesday, January 26


 9:00-10:00 Stan Whitcomb (PPT | PDF)

Gravitational-wave physics and astronomy: the next ten years

Galactic neutron-star population

10:00-10:30 Duncan Lorimer (PDF)

The galactic pulsar population

10:30-10:40 Discussion

10:40-10:45 Lightning Talks (PDF)

Miroslav Shaltev, Prabath Peiris and John Whelan, Vladimir Dergachev, Xavier Siemens

10:45-11:15   Coffee

11:15-11:45 Bruce Allen (KEYNOTE | PDF )

Studying the galactic pulsar population using gravitational waves

11:45-12:00 Discussion

12:00-12:20 Ricardo Ignacio Santiago Prieto (PDF)

Gravitational Radiation Associated with Pulsar Glitches

Pulsar glitches are a potential source of gravitational waves because the brief increase in the pulsar's angular momentum during the glitch can excite various modes in the neutron star. Using data from all known pulsar glitches, we study the possibility of gravitational wave emission at r-mode frequencies. We use a model proposed by Levin and Ushomirsky, which assumes a viscous boundary layer between the crust and the core in the neutron star, to determine the strength of gravitational wave emissions and the signal parameters. We show that r-mode emissions associated with pulsar glitches are a challenging source for detection, even for third generation gravitational wave detectors, though detectable signals are possible from some pulsars.

12:20-12:30 Miltos Vavoulidis (PDF)

Gravitational waves from oscillations of compact stars: what can we learn from current observations?

Oscillating compact stars are promising sources of gravitational radiation. Upper limits on gravitational-wave (GW) burst emission associated with a Vela timing glitch and in coincidence with electromagnetic triggers from magnetars were set recently by the LIGO and Virgo Collaborations. Those searches targeted f-modes of neutron stars with standard equations of state. Indeed, the f-modes are believed to be the principal GW emitters of conventional neutron stars; their high frequencies, though, imply that we would be able to detect only very energetic nearby events. Exotic equations of state, on the other hand, which predict elastic quark matter cores, may be much more interesting. LIGO and Virgo continuous-wave searches are already able to put constraints on the physics of such objects by comparing theoretical models with data analysis (DA) results. In this presentation, we consider this scenario from the GW burst (and not the continuous-wave) point of view. We review the properties of oscillation modes of exotic compact stars with elastic cores. We make estimates on the GW energy output after a corequake and we discuss if/how we can use the latest burst DA results to extract information about the deep interiors of compact stars and/or the underlying physical mechanisms producing glitches and/or flares.

12:30-14:00   Lunch

Neutron Stars and Black Holes

14:00-14:30 Frits Paerels (PPT | PDF)

Mass distribution of neutron stars and the measurement of stellar parameters

14:30-14:40 Discussion

14:40-15:10 Jocelyn Read (PDF)

Constraining the equation of state using advanced gravitational-wave detectors

15:10-15:20 Discussion

15:20-15:30 Lightning Talks (PDF)

Frank Herrmann, Chad Galley, Drew Keppel, Nick Tacik, Izabela Kowalska, Ilana MacDonald, Frank Ohme, Rahul Biswas and Sarah Caudill

15:30-16:00   Coffee

16:00-16:20 Francesco Pannarale (PDF)

Will the inspiral of a black hole-neutron star binary tell us about the nuclear equation of state?

We examine the gravitational-wave signals emitted during the inspiral phase of binary systems composed of a black hole and a neutron star. The influence of the internal structure of the star on the waveform may be characterized in terms of a single parameter, the tidal deformability. We consider whether or not such signals may be distinguished from the ones emitted by binary black holes and, hence, whether information about the neutron star equation of state can be deduced from their detection.

16:20-16:40 Bruno Giacomazzo (KEYNOTE | PDF)

General Relativistic Simulations of Magnetized Binary Neutron Stars

Binary neutron stars are among the most important sources of gravitational waves which are expected to be detected by the current or next generation of gravitational wave detectors, such as LIGO and Virgo, and they are also thought to be at the origin of very important astrophysical phenomena, such as short gamma-ray bursts. I will report on some recent results obtained using the fully general relativistic magnetohydrodynamic code Whisky in simulating equal-mass binary neutron star systems during the last phases of inspiral, merger and collapse to black hole surrounded by a torus. I will in particular describe how magnetic fields can affect the gravitational wave signal emitted by these sources and their possible role in powering short gamma-ray bursts.

16:40-16:55   Coffee

16:55-17:15 Brian Metzger (PDF)

Electromagnetic Counterparts of Neutron Star Mergers Powered by the Radioactive Decay of R-process Nuclei

The most promising astrophysical sources of gravitational waves (GWs) with ground-based interferometers such as LIGO are the inspiral and merger of binary neutron star (NS) and black hole systems. Maximizing the scientific benefits of a GW detection will require identifying a coincident electromagnetic counterpart. One of the most likely sources of isotropic emission from NS mergers is a supernova-like transient powered by the radioactive decay of heavy elements synthesized in the merger ejecta. I will present the first calculations of the optical transients from NS mergers that self consistently determine the radioactive heating using a nuclear reaction network and which determine the resulting light curve with a Monte Carlo radiation transfer calculation. Due to the rapid evolution and low luminosity of NS merger transients, optical counterpart searches triggered by a GW detection will require close collaboration between the GW and astronomical communities. NS merger transients may also be detectable following a short duration Gamma-Ray Burst or “blindly” with present or upcoming optical transient surveys such as the Palomar Transient Factory and Pan-STARRS.

17:15-17:30 Collin Capano (PDF)

The Search for Low Mass Compact Binary Coalescences with the LIGO and Virgo Detectors

I report on the search for gravitational waves from coalescing compact binary systems with total masses between 2 and 35 solar masses using LIGO and Virgo data. I describe the pipeline that is used by the LIGO and Virgo collaborations to search for such waveforms, and I summarize the most recent results that have been obtained using this pipeline.

17:30-17:45 Chad Hanna (PDF)

Gravitational wave search for binary black holes in the nearby Universe

We present the status of the first modeled gravitational-wave search utilizing the complete binary black hole gravitational waveform from inspiral through the merger and ringdown for binaries with negligible component spin. We searched approximately 2 years of LIGO data taken between November 2005 and September 2007 for systems with component masses of 1--99 solar masses and total masses of 25--100 solar masses.

Thursday, January 27

Transient Astronomy I

 9:00- 9:30 Robert Quimby (PDF)

Illuminating Discoveries from Transient Surveys

Wide field optical imaging surveys are uncovering new classes of never before seen (or at least previously over-looked) stellar explosions. Of particular interest are a group of outbursts dwarfing the most powerful supernovae observed in the past century. With peak luminosities in excess of 1044 erg/s and total radiative outputs greater than 1051 erg, these events push the limits of conventional supernova explosion theory. The nature of these events has yet to be established, but it is possible that some of these super-luminous supernovae are triggered by the electron-positron pair instability and they may thus represent local analogs of the first stellar explosions to shape the universe. A second possibility is that they are powered by the spin-down of a nascent magnetar. In this talk, I will highlight some of the key discoveries made by the ROTSE-III and Palomar Transient Factory surveys in this emerging class of events and others. I will present preliminary rates for the super-luminous supernovae, host galaxy constraints, and the prospects for future studies.

 9:30- 9:40 Discussion

 9:40-10:10 Peter Shawhan (PDF)

Prospects for Detection of Gravitational Waves from Supernovae

Core-collapse supernovae liberate a great deal of energy, and there are several possible mechanisms by which some of that energy can be released in the form of gravitational waves. I will discuss the prospects for receiving detectable GW signals from supernovae; search methods that can be used to find them in the GW data; how numerical modeling can help in the detection process; and what the detection (or non-detection) of GWs can tell us about supernova astrophysics.

10:10-10:20 Discussion

10:20-10:30 Lightning Talks (PDF)

Hyung Mok Lee, Sarah Caudill, Shaon Ghosh and Sukanta Bose, Satya Mohapatra, Wen-fai Fong, Daniel Hoak, Shivaraj Kandhasamy, Marc Normandin, Peter Raffai, David Kaplan

10:30-11:00   Coffee

11:00-11:20 Ernazar Abdikamalov (PPT | PDF)

The Gravitational Wave Signature of Collapsar Formation

Long gamma-ray bursts are among the most energetic phenomena in the Universe. There is strong observational evidence linking them with the death of massive stars. However, the details of this relationship and nature of the gamma-ray burst central engine remain uncertain. In this talk, I will present results from 3+1 general relativistic simulations of rotating core collapse in the context of the collapsar model for long gamma-ray bursts. We use a realistic progenitor model with rotation based on stellar evolution calculations and employ a simplified equation of state. Our simulations follow self-consistently collapse, bounce, postbounce evolution, black hole formation, and the subsequent early hyperaccretion phase. We extract gravitational waves from the spacetime curvature and identify a unique gravitational wave signature associated with the early phase of collapsar formation.

11:20-11:40 Jeremiah Murphy (PPT | PDF)

A Model for Gravitational Wave Emission from Neutrino-Driven Core-Collapse Supernovae

Gravitational Wave (GW) detection should offer an unprecedented view into the explosion mechanism of core-collapse supernovae. We investigate the GW emission from postbounce phases of neutrino-driven core-collapse supernovae and identify the most important sources of GWs. These sources are convection, SASI, and asymmetric explosion. For the stages before explosion, we propose a model for the source of GW emission in which convective sinking plumes strike the PNS"surface'' with large speeds and are decelerated by buoyancy forces. In this model, the GW amplitude is set by the magnitude of deceleration and, by extension, the plume's speed. On the other hand, the characteristic frequencies are independent of these speeds. Instead, they are determined by the deceleration timescale, which is set by the buoyancy frequency at the lower boundary of postshock convection. In turn, the buoyancy frequency is determined by the average density of the PNS. Therefore, the characteristic frequencies of GWs encode information about the PNS structure and dense matter equation of state.

11:40-12:00 Konstantin Yakunin (PPT | PDF)

Gravitational Signatures of Core-Collapse Supernova

Core collapse supernovae (CCSN) are among the most promising sources for multi-messenger astronomy. We present results on the gravitational wave (GW) emission in the post-bounce phase of non-rotating core-collapse supernovae obtained from a suite of simulations with the 2D CHIMERA code. Our simulations include the most recent pre-supernova stellar models, multi-frequency neutrino transport coupled with hydrodynamics, both with corrections for general relativistic gravity, as well as a nuclear reaction network, state-of-the-art neutrino emissivities and opacities, and an industry-standard equation of state. Given the presence of explosions in our models, we are able to present complete waveforms, through the explosion phase, based on non-parameterized, first-principles models. Analysis of the GW signature from a Galactic event shows that the signal is within the band-pass of current and future GW observatories and contains features associated with important, singular phenomena such as the Stationary Accretion Shock Instability (SASI), thought to be at the heart of the supernova mechanism. The ability to correlate an observed GW signature with phenomena such as the SASI will allow us to use such observations to diagnose and develop supernova models.

12:00-12:20 James Clark (PDF)

A Search For Gravitational Waves Associated With The August 2006 Timing Glitch Of The Vela Pulsar

The physical mechanisms responsible for pulsar timing glitches are thought to excite quasi-normal mode oscillations in their parent neutron star that couple to gravitational wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two co-located Hanford gravitational wave detectors of the Laser Interferometer Gravitational-wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational wave detection candidate was found. We place Bayesian 90% confidence upper limits of 6.3e-21 to 1.4e-20 on the peak intrinsic strain amplitude of gravitational wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0e44 to 1.3e43 erg.

12:20-12:30 Imre Bartos (PDF)

Scientific Reach and Status of Multimessenger Searches with Gravitational Waves and High-energy Neutrinos

The joint search for gravitational waves (GWs) and high-energy neutrinos (HENs) targets transient cosmic sources. Predicted GW+HEN sources include choked gamma-ray bursts, collapsars, compact binary coalescence, and soft gamma repeaters. Some of these transient sources feature weak or off axis electromagnetic emission, allowing the GW+HEN to give a complementary insight on enigmatic cosmic processes. The talk will provide a review of the status of joint searches with the IceCube-ANTARES-LIGO-GEO600-Virgo global network and will discuss its the methodology and science goals. We also consider the outlook for the science reach for future GW+HEN networks.

12:30-14:00   Lunch

Transient Astronomy II

14:00-14:30 Edo Berger (PDF)

14:30-14:40 Discussion

14:40-15:10 Frederique Marion (PDF)

Status and prospects for detecting Gravitational Waves from Compact Binary Mergers

15:10-15:20 Discussion

15:20-15:30 Lightning Talks(PDF)

Stefanos Giampanis, Lindy Blackburn, Amber Stuver, Marco Drago, Benjamin Farr, Samaya Nissanke, Linqing Wen, Shaun Hooper, Nick Fotopoulos, Satya Mohapatra, Dipongkar Talukder and Sukanta Bose

15:30-16:00   Coffee

16:00-16:20 Mansi Kasliwal (PDF)

Transients in the Local Universe

To effectively search for an electromagnetic (EM) counterpart to a gravitational wave (GW) signal, we must overcome the fundamental challenge of poor GW localization and consequent large number of EM false positives. The simplest solution is to leverage the GW sensitivity limitation to the local universe and restrict the EM follow-up to transients spatially coincident with galaxies known to be in this horizon. Therefore, first, I discuss plans to complete the rather incomplete existing catalog of nearby galaxies. Second, I discuss ongoing efforts with the Palomar Transient Factory to build a complete inventory of all types of transients in the local universe. This would enable us to unambiguously associate the physical nature of the candidate EM event with the GW signal.

16:20-16:35 Lucia Santamaria (PDF)

Multimessenger Search for Gravitational Waves from Core-Collapse Supernovae

Core-collapse supernovae (CCSNe) are considered to be among the most energetic astrophysical sources of gravitational waves (GWs), but so far there has been no dedicated multimessenger GW CCSN search. In this talk, a method for optically-triggered searches for GW bursts associated with CCSNe using ground-based GW interferometers is presented. The method uses optical observations of SNe in the local Universe (at distances of 3--10 Mpc) as triggers for an excess power search in the output of a network of GW detectors. We provide distance sensitivity estimates for GW waveforms from recent numerical simulations of CCSN as well as from three extreme analytical models. We discuss the prospects for constraining the CCSN mechanism with available optical triggers from extragalactic SNe with current and future detectors, and with a galactic event accompanied by neutrinos.

16:35-16:50   Coffee

16:50-17:02 Brennan Hughey (PDF)

Electromagnetic Follow-ups of Candidate Gravitational Wave Triggers in the Recent LIGO and Virgo Science Runs

During the recently completed LIGO-Virgo science runs, triggers produced by the gravitational wave interferometer network were sent out for follow-up observations by electromagnetic (EM) telescopes. We present a brief overview of this prototype EM follow-up program, from rapid online gravitational wave data analysis to telescope response, and highlight some of our partner telescopes.

17:02-17:14 Larry Price (KEYNOTE | PDF)

The Low-Latency Search for Gravitational Waves from Compact Binary Coalescence

During the summer of 2010, the first low-latency search for gravitational waves from compact binary coalescences was performed using the LIGO and Virgo instruments. The aim was to provide triggers for follow-up by electromagnetic telescopes. In this presentation we will describe the low-latency pipeline used to produce these triggers, including the time-delay-based procedure used to localize them on the sky.

17:14-17:26 Jonah Kanner (PDF)

Performance study of the first low latency joint EM/GW search

The LIGO and Virgo collaborations performed the first systematic EM follow-up observations guided by GW interferometers during several months in 2009 and 2010. To characterize the ability of this search to correctly identify and image source positions, we perform a Monte Carlo study with ad-hoc, or "Burst", waveforms, and the full low-latency Burst pipeline. As in the actual search, a catalog of nearby galaxies is used to reduce the search area. We investigate how position reconstruction success varies with both GW signal strength and choice of EM hardware.

17:26-17:35 Discussion

Friday, January 28

Observational Strategies and Instrumentation I

 9:00- 9:30 Sam Waldman (PDF)

Observational strategies for the next generation of gravitational-wave detectors

 9:30-10:00 Dale Frail (PDF)

Current and Future Capabilities for Radio Searches of Gravitational Wave Counterparts

10:00-10:30 Joshua Bloom (KEYNOTE | PDF)

Wide-field Surveys

10:30-11:00   Coffee

11:00-11:30 Duncan Galloway (PDF)

X-ray Observatories

11:30-12:00 Masayuki Nakahata (PDF)

Neutrino Observatories

12:00-12:20 Discussion

12:20-12:30 Lightning Talks (PDF)

Antonis Mytidis, Nickolas Fotopoulos, Thilina Dayanga and Sukanta Bose, Ting Zhang and Soma Mukherjee, Paul T Baker, Papia Rizwan and Soma Mukherjee, Tanner Prestegard, Michael Coughlin, Ayaka Shoda

12:30-14:00   Lunch

Open Data, Supermassive black holes and Data Analysis Methods

14:00-14:30Roy Williams (PDF)

Led Discussion: LIGO Open Data - what would you like?

14:30-14:50 Nicholas Stone (PDF)

Prompt Tidal Disruption of Stars as an Electromagnetic Signature of Supermassive Black Hole Coalescence

A precise electromagnetic measurement of the sky coordinates and redshift of a coalescing black hole binary holds the key for using its gravitational wave signal to constrain cosmological parameters and to test general relativity. Here we show that the merger of ~10^{6-7}M_sun black holes is generically followed over a period of years by multiple electromagnetic flares from tidally disrupted stars. The sudden recoil imparted to the merged black hole by GW emission promptly fills its loss cone and results in a tidal disruption rate of stars as high as ~0.1 per year. The prompt disruption of a single star within a galaxy provides a unique electromagnetic flag of a recent black hole coalescence event, and sequential disruptions could be used on their own to calibrate the expected rate of GW sources for pulsar timing arrays or the proposed Laser Interferometer Space Antenna.

14:50-15:10 Tanja Bode (PDF)

Electromagnetic Emissions from Merging Supermassive Black Hole Binaries

Synergistic electromagnetic (EM) and gravitational wave (GW) observations from the coalescence of supermassive black holes (SBHs), considered to be the next observational frontier, will shed light on galaxy assembly and SBH growth. Computational modeling of the dynamics and accretion processes in this last evolutionary stage of SBH binaries is central to understanding the conditions under which EM emission accompanies GWs. On scales smaller than ~0.01pc for a 10^7 solar mass binary, gravitational wave emission determines the orbital dynamics of SBH binaries and therefore EM emissions can only be studied within the context of fully relativistic simulations. We present results from fully general relativistic hydrodynamics simulations of the late inspiral and merger of SBH binaries within astrophysically relevant gaseous environments including circumbinary disks and hot, radiatively inefficient accretion flows. We find that the observability and characteristics of EM signatures are intricately connected to the physical properties of the binary and its environment. For instance, a sudden drop in EM luminosity will not only signal the merger of the SBHs but also the presence of hot, radiatively inefficient accretion flows, whereas dramatic changes in spectral emission lines close to the coalescence may signal the presence of a circumbinary disk.

15:10-15:25 Larne Pekowsky (PDF)

Status of the NINJA-2 project

Two important advances have occurred in recent years which have brought us closer to the goal of observing and interpreting gravitational waves from coalescing compact objects: the successful construction and operation of a world-wide network of ground-based gravitational-wave detectors and the impressive success of numerical relativity in successfully simulating the merger phase of Binary Black Hole (BBH) coalescence. The aim of the NINJA project is to study the sensitivity of gravitational-wave analysis pipelines to numerical simulations of waveforms and foster close collaboration between numerical relativists and data analysts. NINJA-1 was a huge success, over 75 numerical relativists and data analysis participated in the contribution of a simulated data set containing numerical waveforms, analysis of this data and interpreting the results of this analysis. We present the goals and status of the followup project, NINJA-2, which is currently ongoing.

15:25-15:35 Lightning Talks (PDF)

Valentin Necula, Chris Messenger, Jordi Burguet-Castell, Christian Roever, Cesar Costa, Kari Hodge, Nelson Christensen, Reinhard Prix

15:35-16:00   Coffee

16:00-16:15 Eric Thrane (PDF)

Stochastic Transient Algorithm Multi-detector Pipeline

I review mechanisms for the emission of long gravitational-wave (GW) transients lasting >1s, which cannot presently be modeled with matched filtering templates. Possible mechanisms for such long GW bursts include instabilities in and fragmentation of accretion discs following core-collapse supernovae, instabilities in binary inspiral remnants and in isolated neutron stars and other phenomena such as pulsar glitches and magnetar flares. I report on progress for searches for long GW transients with the Stochastic Transient Algorithm Multi-detector Pipeline (STAMP).

16:15-16:30 Ruslan Vaulin (PDF)

Detecting transient gravitational-wave signals with multiple, partially redundant searches

A variety of astrophysical sources are capable of producing transient gravitational-wave signals detectable by ground-based gravitational-wave detectors. Consequently, multiple searching techniques are used to analyze the same experimental data and typically, despite significant differences in design and responses to signals and non-Gaussian noise artifacts, are sensitive to the same sources. We discuss a problem of interpreting results of multiple, partially redundant searches for transient gravitational-wave signals. This problem may be addressed within the general framework of statistical theory of signal detection if each search is treated as a classifier for a given event. Using this approach we show how results of searches can be combined. We derive optimal statistic for the joint search and demonstrate that it improves the overall sensitivity to gravitational-wave signals and also resolves interpretational issues arising in the case of the multiple searches.

16:30-16:45 Chris Pankow (PDF)

Statistic for Combination of Results from Multiple Gravitational Wave Searches

Numerous searches for gravitational waves have been performed in recent years, covering multiple data epochs from several gravitational wave detectors. Each search may estimate detection significance and astrophysical rates in different ways, but the estimate should take into account both the background and the intrinsic search sensitivity. These measurements determine the significance of the observation and shape the upper limit on source event rates. If searches target the same source, it is important to be able to compare and combine the results of the various searches. Therefore, we propose a statistic which combines any number of searches into a single measurement by taking into account both the sensitive volume of a search and the background event rate into a "false alarm rate density". This method allows the comparison of a putative gravitational wave candidate in the context of a combined search over different epochs of data with possibly very different characteristics. We present an example of this technique using the results from simulated gravitational-wave detector networks.

16:45-17:00 Marc van der Sluys (PDF)

Using astrophysical knowledge in gravitational-wave data analysis of binary inspirals

The LIGO-Virgo collaboration has at its disposal three independent kilometre-scale gravitational-wave (GW) interferometers: the two LIGO detectors in the USA and Virgo in the EU. After upgrades and commissioning in the last two years, these interferometers are now in their enhanced stage, and roughly twice as sensitive as the initial detectors. While much effort is undertaken to search for GW signals in the data, our work focuses on the detailed follow-up analysis of candidate compact-binary coalescence (CBC) events found in such searches. Extracting astrophysically relevant data from CBC events, signals from inspiralling black-hole and/or neutron-star binaries, after detection is a time-consuming process, mainly due to the large dimensionality of the parameter space. We developed a Markov-chain Monte-Carlo code called SPINspiral that can do parameter estimation on signals detected by LIGO and Virgo. In this presentation, I will discuss the techniques we use and focus on the way we can use prior astrophysical knowledge to optimise the parameter estimation by constraining some of the parameters. I will discuss to what extent this results in a more accurate determination of the other parameters, and how this speeds up the process of parameter estimation.

17:00-17:15 Shaun Hooper (PDF)

Summed Parallel Infinite Impulse Response (SPIIR) Filters For Low-Latency and Efficient Gravitational Wave Detection

Advanced gravitational wave detectors are expected to make the first detection in the next decades. Prompt electromagnetic follow-up observations of gravitational wave (GW) events will require low-latent GW triggers. I will present a new time-domain low-latency algorithm for detecting GWs from coalescing binaries of compact objects using infinite impulse response (IIR) filters. I will show that with a good choice of filter coefficients, the summation of a bank of IIR filters can approximate the value of the signal to noise ratio up to 99% that from the optimal matched filter method, whilst maintaining similar the detection efficiency. I will also compare the computational efficiency of this method to the frequency domain matched filtering approach, and discuss the implication for advanced detectors.

17:15-17:25 Kenshi Okada (PDF)

Magnetic coupling noise in a Torsion-bar Antenna for Gravitational wave Observations

We present a new type of gravitational wave detector called torsion-bar antenna. Our detector is formed by the bar-shaped test mass that is rotated by gravitational waves and laser interferometric sensor to monitor the differential angular fluctuation. Superconducting magnetic levitation is used for the suspension of the test mass, since it has many advantages, such as zero mechanical loss and resonant frequency around its suspension axis in an ideal situation. These advantages enable us to probe low-frequency gravitational waves below 1 Hz even with the ground-based configuration. But superconducting magnetic levitation also brings about a detector noise from the coupling of external magnetic field and the magnet attached to the test mass. We developed a prototype detector and evaluated the noises including magnetic coupling noise. It is revealed that the current detector noise is determined by magnetic coupling noise below around 0.1 Hz. This result indicates that the current detector noise will be reduced if we enclose the detector by a magnetic shield. The details of these experiments will be explained in this presentation.

Saturday, January 29

Testing General Relativity

 9:00- 9:30 Ingrid Stairs (PPT | PDF)

Testing general relaltivity with relativistic binary pulsars

 9:30- 9:45 Discussion

 9:45-10:15 Nico Yunes (KEYNOTE | PDF)

Probing Strong Field Physics with Gravitational Waves

10:15-10:30 Discussion

10:30-11:00   Coffee

11:00-11:15 Carl Rodriguez (PDF)

Testing the No-Hair Theorem with Intermediate Mass Ratio Inspirals in Advanced LIGO

The inspiral of a neutron star or stellar-mass black hole into an intermediate-mass black hole (IMBH) (~50 msun to ~350 msun) promises an entirely new look at strong field gravitational physics. These intermediate mass ratio inspirals (IMRIs), which may be detectable at rates of up to a few tens per year in the advanced detector era, will encode information about the spacetime of the central body. Direct observation of the gravitational waves emitted during IMRIs will allow us to test the "no-hair" theorem of general relativity, and therefore to test if the central IMBH is a Kerr black hole. Using modified post-Newtonian waveforms, we explore the prospects for constraining the central body's mass quadrapole moment in Advanced LIGO. We use the Fisher information matrix to estimate the accuracy with which the parameters of the central body can be measured. We find that for some mass and spin combinations, the quadrupole moment can be measured to within a fraction of its Kerr value, allowing for accurate tests of deviations of the central body from a Kerr black hole.

11:15-11:30 Kazuhiro Hayama (PDF)

Test of scalar-tensor gravity theory from observations of gravitational wave bursts with advanced detector network

We consider tests of relativistic gravity theory from observations of gravitational wave bursts. Tests of gravity theory are a fundamental physics issue, and one of the plausible alternative gravity theories is scalar-tensor theory. A significant difference between the scalar-tensor theory and general relativity is the existence of a scalar field which is connected with the gravity field with coupling parameters, and a resulting scalar gravitational wave. We present a fully implemented pipeline to detect a scalar gravitational wave and discuss constraints on the coupling parameters using simulated noise of advanced LIGO, advanced Virgo, LCGT and LIGO-Australia.

11:30-11:45 Ilya Mandel (PDF)

The Distribution of Coalescing Compact Binaries in the Local Universe: Prospects for Gravitational-Wave Observations

Merging compact binaries are among the most exciting candidates for gravitational-wave (GW) detection by a network of ground-based observatories, including LIGO and Virgo. In anticipation of the first detections, the expected distribution of these GW sources in the local universe is of considerable interest. We investigate the distribution of coalescence sites for neutron-star binaries using dark matter simulations of structure formation. These binary systems may acquire large barycentric velocities at birth ("kicks"). This results in merger site distributions that are more diffusely distributed with respect to their putative hosts, with mergers occurring out to distances of a few Mpc from the host halo. Redshift estimates based solely on the nearest galaxy in projection can, as a result, be inaccurate. On the other hand, large offsets from the host galaxy could aid the detection of faint optical counterparts and should be considered when designing strategies for electromagnetic observations to follow up likely GW triggers. The degree of isotropy in the projected sky distributions of GW sources is found to be significantly enhanced if progenitor systems possess large kicks as inferred from the known population of pulsars and double compact binaries. Even in the absence of observed electromagnetic counterparts, the differences in sky distributions of binaries produced by disparate kick-velocity models could be discerned by GW observatories, within the expected accuracies and detection rates of advanced LIGO -- in particular with the addition of more interferometers, such as LIGO Australia, to the network.

11:45-12:00 Will Farr (PDF)

The Mass Distribution of Stellar-Mass Black Holes: Robust Constraints through Model Selection

Until the first gravitational wave detection involving a stellar-mass black hole, X-ray binary systems provide the only observational window on the properties of these objects. We have used a sample of fifteen low-mass X-ray binary systems and five high-mass X-ray binary systems for which dynamical measurements of the black hole mass exist to place constraints on the mass distribution of stellar-mass black holes. We fit the low-mass X-ray binary black hole masses alone and the combined sample of twenty black hole masses to five parametric and five non-parametric models for the underlying mass distribution. We can extract useful information from this plethora of models because of new techniques we developed that allow for the efficient calculation of the relative Bayesian posterior probabilities of the models. Surprisingly from a theoretical perspective, we find strong evidence in both the low-mass and combined samples for a "mass gap" between the maximum neutron star mass of ~3 solar masses and the minimum black hole mass, in agreement with studies from other groups; we find the minimum black hole mass to be 4.3 solar masses for the best-fitting model of the low-mass X-ray binaries and 4.5 solar masses for the best-fitting model of the combined sample (both at 90% confidence).

12:00-12:15 Thomas Bulik (PDF)

Observational estimate of the binary black hole coalescence rate

We investigate the future evolution of two extragalactic X-ray binaries: IC10~X-1 and NGC300~X-1. Each of them consists of a high mass BH (sim 20-30 msun) accreting from a massive WR star companion (gtrsim 20 msun), and both are located in low metallicity galaxies. We analyze the current state of the systems and demonstrate that both systems will very quickly (less than or similar to 0.3 Myr) form close BH-BH binaries with the short coalescence time (sim 3 Gyr) and large chirp mass (sim 15 msun). As there are two such immediate BH-BH progenitor systems within 2 Mpc and as the current gravitational wave instruments LIGO/VIRGO (initial stage) can detect such massive BH-BH mergers out to sim 200 Mpc, the empirically estimated detection rate of such inspirals is R=3.36^{+8.29}_{-2.92} at the 99% confidence level.

12:15-12:30 Michal Dominik (PDF)

The Effect of Metallicity on the Detection Prospects for Gravitational Waves

Data from the Sloan Digital Sky Survey (~300,000 galaxies) indicate that recent star formation (within the last 1 billion years) is bimodal: half of the stars form from gas with high amounts of metals (solar metallicity) and the other half form with small contribution of elements heavier than helium (~10%-30% solar). Theoretical studies of mass loss from the brightest stars derive significantly higher stellar-origin black hole (BH) masses (~30-80 M sun) than previously estimated for sub-solar compositions. We combine these findings to estimate the probability of detecting gravitational waves (GWs) arising from the inspiral of double compact objects. Our results show that a low-metallicity environment significantly boosts the formation of double compact object binaries with at least one BH. In particular, we find the GW detection rate is increased by a factor of 20 if the metallicity is decreased from solar (as in all previous estimates) to a 50-50 mixture of solar and 10% solar metallicity. The current sensitivity of the two largest instruments to neutron star-neutron star (NS-NS) binary inspirals (VIRGO: ~9 Mpc; LIGO: ~18) is not high enough to ensure a first detection. However, our results indicate that if a future instrument increased the sensitivity to ~50-100 Mpc, a detection of GWs would be expected within the first year of observation. It was previously thought that NS-NS inspirals were the most likely source for GW detection. Our results indicate that BH-BH binaries are ~25 times more likely sources than NS-NS systems and that we are on the cusp of GW detection.

UWM Center for Gravitation and Cosmology | |