Gravitation and Multimessenger Astrophysics

Gravitational waves originate from the most violent cosmic events, which are often hidden from traditional means of observation. Starting with the first direct observation of gravitational waves in the coming years, astronomy will become richer with a new messenger that can help unravel many of the yet unanswered questions on various cosmic phenomena. The ongoing construction of advanced gravitational wave observatories requires disruptive innovations in many aspects of detector technology in order to achieve the sensitivity that lets us reach cosmic events. We present the development of a component of this technology, the Advanced LIGO Optical Timing Distribution System. This technology aids the detection of relativistic phenomena through ensuring that time, at least for the observatories, is absolute. Gravitational waves will be used to look into the depth of cosmic events and understand the engines behind the observed phenomena. As an example, we examine some of the plausible engines behind the creation of gamma ray bursts. We anticipate that, by reaching through shrouding blastwaves, efficiently discovering off-axis events, and observing the central engine at work, gravitational wave detectors will soon transform the study of gamma ray bursts. We discuss how the detection of gravitational waves could revolutionize our understanding of the progenitors of gamma ray bursts, as well as related phenomena such as the properties of neutron stars. One of the most intriguing directions in utilizing gravitational waves is their combination with other cosmic messengers such as photons or neutrinos. We discuss the strategies and ongoing efforts in this direction. Further, we present the first observational constraints on joint sources of gravitational waves and high energy neutrinos, the latter of which is created in relativistic plasma outflows, e.g., in gamma ray burst progenitors. High energy neutrinos may be created inside a relativistic outflow burrowing its way out of a massive star from the star's collapsed core. We demonstrate how the detection of high energy neutrinos can be used to extract important information about the supernova/gamma-ray burst progenitor structure. We show that, under favorable conditions, even a few neutrinos are sufficient to probe the progenitor structure, opening up new possibilities for the first detections, as well for progenitor population studies. We present the science reach and method of an ongoing search for common sources of gravitational waves and high energy neutrinos using the initial LIGO/Virgo detectors and the partially completed IceCube detector. We also present results on the sensitivity of the search. We argue that such searches will open the window onto source populations whose electromagnetic emission is hardly detectable

Developing Tools for Multimessenger Gravitational Wave Astronomy

We present work in progress to craft open-sourced numerical tools that will enable the calculation of electromagnetic counterparts to gravitational waveforms: the {\tt GiRaFFE} (General Relativistic Force-Free Electrodynamics) code. {\tt GiRaFFE} numerically solves the general relativistic magnetohydrodynamics system of equations in the force-free limit, to model the magnetospheres surrounding compact binaries, in order (1) to characterize the nonlinear interaction between the source and its surrounding magnetosphere, and (2) to evaluate the electromagnetic counterparts of gravitational waves, including the production of collimated jets. We apply this code to various configurations of spinning black holes immersed in external magnetic field, in order to both test our implementation, and to explore the effect of strong gravitational field, high spins and of misalignment between the magnetic field lines an black hole spin, on the electromagnetic output and the collimation of Poynting jets. We will extend our work to collisions of black holes immersed in external magnetic field, which are prime candidates for coincident detection in both gravitational and electromagnetic spectra.Comment: 6 pages, 6 figures, MG15 proceeding

Multimessenger Potential of the Radio Neutrino Observatory in Greenland

The Radio Neutrino Observatory in Greenland (RNO-G) is the only ultrahigh energy (UHE, ${\gtrsim}30$~PeV) neutrino monitor of the Northern sky and will soon be the world's most sensitive high-uptime detector of UHE neutrinos. Because of this, RNO-G represents an important piece of the multimessenger landscape over the next decade. In this talk, we will highlight RNO-G's multimessenger capabilities and its potential to provide key information in the search for the most extreme astrophysical accelerators. In particular, we will highlight opportunities enabled by RNO-G's unique field-of-view, its potential to constrain the sources of UHE cosmic rays, and its complementarity with IceCube at lower energies