The Advanced LIGO detectors have achieved the long-sought goal of directly detecting gravitational waves, in line with a century-old prediction of Einstein's general theory of relativity. The dramatic detection of the first few signals in late 2015 also opened our ears to the existence of black holes with up to about 36 times the mass of our sun, in binary orbits close enough to merge with a huge release of energy in the form of gravitational waves. However, this has only scratched the surface of what gravitational-wave signals may be out there and what we can learn from them. The research supported by this award will take full advantage of the new capabilities as the Advanced LIGO detectors improve and are joined by similar facilities in Italy, Japan and eventually India. The goal is to enhance communication and cooperation with the broader astronomy community so that the astronomical community can use all the modern tools of astronomy, from optical and radio telescopes on the ground to X-ray and gamma-ray detectors on spacecraft, to find and study the sources of LIGO's gravitational-wave signals through the electromagnetic energy and/or neutrinos that they may also emit. Specifically, this effort will help to improve the analysis software and procedures to select promising events more rapidly and reliably, with better monitoring, and to produce prompt public alerts for strong, clear events. This group will collaborate on searches for gamma-ray, X-ray and radio bursts matching up with gravitational-wave events, as well as explore how best to use the growing network of gravitational-wave detectors to search for "scalar" gravitational-wave bursts, which would be a distinctive sign that Einstein's theory is not the whole story about gravity. Finally, the PI will share his expertise and develop fun and educational hands-on activities for children and their parents to learn about science through a Family Discovery Days outreach program.
The LIGO-Virgo "EM follow-up program" has enlisted over 90 partner groups who have shown a strong response to the gravitational-wave events and candidates shared with them so far, but several technical aspects of the program need improvement. Building on this group's experience with the current event selection and alert generation software and procedures, the PI will help re-implement the system to be faster, more robust, easier to monitor, and ready to generate both public and private alerts during the future observing runs of the advanced gravitational-wave detector network. This group is currently discussing with LIGO and Virgo collaborators how best to manage the system design, software development and testing which will be needed. In parallel, they are working with the Fermi mission science team and LWA radio observatory users to search for gamma-ray bursts and radio transients that may be the counterparts of gravitational-wave signals, in both triggered and un-triggered search modes. According to various models, binary mergers involving at least one neutron star are likely to produce emissions across the electromagnetic spectrum, although they may be challenging to detect and to definitively identify as the counterpart. It remains an open question whether binary black hole mergers, like the events detected by LIGO so far, produce detectable emissions. To test whether general relativity (GR) is the correct theory of gravity, the PI will use a modified version of the WaveBurst algorithm to search for gravitational-wave bursts with a scalar strain polarization, distinct from the tensor polarization states which are the hallmark of GR. The group will investigate both all-sky and position-constrained (when a possible counterpart has been identified) searches; the latter can also enable a test of whether the waves travel at the speed of light (as predicted by GR) or not.
