Matthew J. Benacquista

Gravitational Radiation from Pulsating White Dwarfs

Rotating white dwarfs undergoing quasi-radial oscillations can emit gravitational radiation in a frequency range from 0.1 to 0.3 Hz. Assuming that the energy source for the gravitational radiation comes from the oblateness of the white dwarf induced by the rotation, the strain amplitude is found to be ~10-27 for a white dwarf at ~50 pc. The Galactic population of these sources is estimated to be ~107 and may produce a confusion-limited foreground for proposed advanced detectors in the frequency band between space-based and ground-based interferometers. Nearby oscillating white dwarfs may provide a clear enough signal to investigate white dwarf interiors through gravitational wave asteroseismology.

Gravitational Radiation from Globular Clusters

Space-based gravitational wave detectors will have the ability to observe continuous low-frequency gravitational radiation from binary star systems. They can determine the direction to continuous sources with an angular resolution approaching tens of arcminutes. This resolution should be sufficient to identify binary sources as members of some nearby globular clusters. Thus, gravitational radiation can be used to determine the population of hard binaries in globular clusters. For particularly hard binaries, the orbital period may change as a result of gravitational wave emission. If one of these binaries can be identified with a globular cluster, then the distance to that cluster can be determined. Thus, gravitational radiation may provide reddening-independent distance measurements to globular clusters and the RR Lyrae stars that inhabit them.

Gravitational Radiation from Fluctuations in Rotating Neutron Stars

Undamped quasiradial fluctuations of rotating neutron stars and the gravitation radiation generated by them are discussed. Two possible sources of energy for maintaining these fluctuations are mentioned: the energy of deformation of the decelerating neutron star (spin down) and the energy released during a jump in the stars angular velocity (glitch). Expressions are derived for the intensity of the gravitational radiation and the amplitude of a plane gravitational wave for an earthbound observer. Estimates of these quantities are obtained for the Vela and Crab pulsars, for which the secular variation in the angular velocity is most often accompanied by irregular variations. It is shown that gravitational waves from these pulsars could be detected by the new generation of detectors.

Consequences of Disk Scale Height on LISA Confusion Noise from Close White Dwarf Binaries

Gravitational radiation from the Galactic population of close white dwarf binaries (CWDBs) is expected to produce a confusion-limited signal at the lower end of the sensitivity band of the Laser Interferometer Space Antenna (LISA). The canonical scale height of the disk population has been taken to be 90 pc for most studies of the nature of this confusion-limited signal. This estimate is probably too low, and the consequences of a more realistic scale height are investigated with a model of the LISA signal due to populations of CWDBs with different scale heights. If the local space density of CWDBs is held constant, increasing the scale height results in both an increase in the overall strength of the confusion-limited signal as well as an increase in the frequency at which the signals become individually resolvable. If the total number of binaries is held constant, increasing the scale height results in a reduction of the number of expected bright signals above the confusion-limited signal at low frequencies. We introduce an estimator for comparing this transition frequency that takes into account the signal spreading at higher frequencies.

Gravitational radiation from differentially rotating white dwarfs

We examine the possibility of gravitational radiation from white dwarfs undergoing self-similar oscillations which are fed by the energy of the differential rotation of the white dwarf. We consider two typical cases of angular momentum distribution. Assuming the energy of the self-similar oscillations causing gravitational wave emission is about 1% of the energy dissipated in the differentially rotating white dwarf, the strain amplitudes are found to be less than 10−27 for a white dwarf at ~50 pc. Combined with the mechanism of gravitational radiation based on deformation energy from magnetic white dwarfs, the gravitational radiation from differentially rotating white dwarfs may produce a confusion limited foreground above the stochastic cosmological background for proposed advanced detectors in the decihertz frequency band.

Preparing for LISA Data: The Testbed for LISA Analysis Project

The Testbed for LISA Analysis (TLA) Project aims to facilitate the development, validation, and comparison of different methods for LISA science data analysis by the broad LISA Science Community to meet the special challenges that LISA poses. It includes a well‐defined Simulated LISA Data Product (SLDP), which provides a clean interface between the modeling of LISA, the preparation of LISA data, and the analysis of the LISA science data stream; a web‐based clearinghouse (at 〈http://tla.gravity.psu.edu〉) providing SLDP software libraries, relevant software, papers and other documentation, and a repository for SLDP data sets; a set of mailing lists for communication between and among LISA simulator developers and LISA science analysts; a problem tracking system for SLDP support; and a program of workshops to allow the burgeoning LISA science community to further refine the SLDP definition, define specific LISA science analysis challenges, and report their results. This proceedings paper describes the TLA Pr...

A How-To for the Mock LISA Data Challenges

The LISA International Science Team Working Group on Data Analysis (LIST‐ WG1B) is sponsoring several rounds of mock data challenges, with the purpose of fostering development of LISA data‐analysis capabilities, and of demonstrating technical readiness for the maximum science exploitation of the LISA data. The first round of challenge data sets were released at this Symposium. We describe the models and conventions (for LISA and for gravitational‐wave sources) used to prepare the data sets, the file format used to encode them, and the tools and resources available to support challenge participants.The LISA International Science Team Working Group on Data Analysis (LIST-WG1B) is sponsoring several rounds of mock data challenges, with the purpose of fostering development of LISA data-analysis capabilities, and of demonstrating technical readiness for the maximum science exploitation of the LISA data. The first round of challenge data sets were released at this Symposium. We describe the models and conventions (for LISA and for gravitational-wave sources) used to prepare the data sets, the file format used to encode them, and the tools and resources available to support challenge participants.

Searching for quasi-periodic gravitational waves from low mass x-ray binaries with AURIGA

Astrophysical models indicate that low mass x-ray binaries (LMXBs) are very promising as sources of continuous, quasi-periodic gravitational waves at high frequencies, such as those at which resonant bar detectors are operating. In this preliminary paper we quickly derive the expected amplitude of the gravitational wave signals. We show that it is likely that there may be some objects emitting in the AURIGA band. We are producing a database of possible sources and identifying the most promising ones. Our preliminary result indicates that we can achieve a good sensitivity with an observation time of about 10 days thanks to the improved sensitivity of the upgraded AURIGA detector. We also show what will be possible to perform with the advanced resonant detectors (DUAL). Finally, we briefly outline the general features of the analysis method we intend to apply postponing to a future paper the detailed discussion.

Observing Globular Cluster Binaries with Gravitational Radiation

Ultracompact binaries are expected to be the best candidates for continuous gravitational radiation in the frequency range of space-based gravity wave detectors such as LISA. The dynamics of globular cluster evolution are expected to enhance the population of such binaries in globular clusters. We present the nature of the globular cluster population of binaries which will be detectable by LISA as well as the fraction of the galactic globular cluster system which can be explored by LISA.

Globular cluster distance measurements with LISA

The dynamics of globular cluster evolution is thought to favor the production of hard binary systems in the cluster core. Binaries containing two degenerate objects will be detectable by LISA with a signal to noise ratio above 10. Very short period binaries with orbital periods below about 500 s will have a measurable frequency change (or chirp) due to inspiral during a one year integration. Using the measured chirp, it is possible to determine the distance to the binary with better than 10% precision if the angular position is known. Consequently, it is shown that globular cluster distances can be measured accurately using gravitational radiation.