Current understanding of coalescing binary black holes and neutron stars suggests that Advanced LIGO (AdvLIGO) should detect somewhere between a few to several of these systems per year, thus, ushering in the age of gravitational-wave astronomy. Some of these systems are expected to be visible to electromagnetic observatories as well. Smart hardware and software tools will be developed so that an astrophysical signal observed in AdvLIGO and the advanced Virgo detector can be followed-up rapidly by pointing the electromagnetic observatories at its source, while it is still active. The complete characteristics of the signal, as made available recently through a combination of analytical solutions and numerical-relativity breakthroughs, will be used in the search for these binaries.
Together, these multi-messenger observations, which use complementary gravitational-wave and electromagnetic data, promise to resolve some outstanding puzzles in astronomy, such as the origin of the short duration gamma-ray bursts and the nature of dark energy. This quest will be aided by the establishment of an experimental effort at the main campus of the Washington State University (WSU) in Pullman, and could foster the growth of Physics and Astronomy education at WSU-Tri-Cities (WSU-TC), located near the site of the LIGO Hanford Observatory. That campus community has a large Hispanic population with nearby Native American communities. The co-placement of LIGO and WSU-TC in this community offers a rare setting for integrating university education with cutting edge research.
This award supported multiple projects related to the characterization of the detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) and the analysis of their data for detecting gravitational-wave (GW) signals. First, we contributed to the search for GW signals from binaries of compact objects, i.e., black holes and neutron stars, in the data of ground-based detectors LIGO and Virgo. One search focused on signals from binary mergers with a total mass between 2 and 35 solar masses. While no GW signals were detected, upper limits on the rate of mergers was obtained: The cumulative 90%-confidence upper limits on the rate of compact binary coalescence were found for non-spinning binary neutron stars, black hole-neutron star systems, and binary black holes to be 8.7e-3, 2.2e-3 and 4.4e-4 per year per L_10, respectively, where L_10 is 10 billion times the blue solar luminosity. We also searched approximately 2 years of LIGO data taken between November 2005 and September 2007 for binary systems with component masses of 1-99 solar masses and total masses of 25-100 solar masses. We constrain the rate of mergers for binary black hole systems with component masses between 19 and 28 solar masses and negligible spin to be no more than 2.0 per megaparsec-cubed per million-year at 90% confidence. Second, we also contributed to the search for a stochastic GW background in a frequency band of 600-1000 Hz of the LIGO-Virgo detectors. We obtained a 95% upper limit on the amplitude of the frequency (f) dependent GW density parameter, Omega(f) = Omega_3 (f/900Hz)^3, of Omega_3 < 0.33, assuming a value of the Hubble parameter of h_100=0.72. These new limits are a factor of seven better than the previous best in this frequency band. Third, we developed techniques for improving the performance of the data analysis methods for searching GW signals from compact binary coalescences in LIGO-Virgo data and implemented them on the data taken during the last few science runs (namely, LIGO's fifth and sixth science runs S5 and S6 and Virgo's first three science runs VSR1, VSR2, and VSR3) conducted by those observatories. We also developed a targeted search for a stochastic gravitational-wave background from a population of neutron stars in the Virgo cluster. We expect to publish the results from those searches in about a year from now. Fourth, we contributed to the commissioning of the Advanced LIGO detectors. Those detectors are expected to be ten times more sensitive to GW signals from coalescing binary neutron stars than Initial LIGO. We also analyzed the causes in the past science runs of the LIGO detectors losing 'lock', which is the resonant condition that allows a detector to operate. Lessons learned there may reduce lock-loss in the Advanced LIGO detectors as well. Finally, we continued to engage in public outreach activities in Pullman and the Tri Cities, WA, through the Washington State University planetarium and the Jewett Observatory and science exhibits located in LIGO Hanford. We also gave Public Talks and lectures in international Schools and Workshops in Gravitational Wave Astronomy.
