Astrophysical Multimessenger Observatory Network Enables New Ways of Seeing Violent Cosmic Events

Among the creation gods of ancient Egypt, Ra, the Sun God, was master of the physical, concrete world. Amon represented all of the subtle or unseen elements of creation. Together they formed a composite god called Amon-Ra meaning "hidden light." That, says Penn State physicist Miles Smith, is what the AMON project seeks to reveal—subtle aspects of the universe that have never been observed before.

AMON stands for Astrophysical Multimessenger Observatory Network. Its mission is to form a network of high-energy observatories across the globe that will search for previously unseen astrophysical signals and send alerts to more traditional telescopes in order to corroborate the possible celestial events.

Until the early 20th Century, astronomers relied almost exclusively on visible light to view the sky. Their telescopes, though steadily increasing in power, were no different in this respect from the ones used by Galileo in 1610. Today we see much more of the universe by observing light from all across the electromagnetic spectrum. Gamma-ray-, x-ray-, infrared-, and radio-astronomy have revolutionized astronomical observation, as have the advent of space-based telescopes to complement those on the ground.

These new ways of seeing allowed the observation of violent cosmic events which, because of their transience, were previously undetectable, such as supernovas, gamma ray bursts, and collisions between black holes.

In addition, the past 50 years have seen tremendous progress in the sensitivity of instruments to detect cosmic rays—high-energy charged particles from outer space, such as protons and charged nuclei. Particle accelerators have enabled physicists to create, detect, and analyze other sub-atomic particles, such as neutrinos. These alternative messengers—particles that survive across vast distances in space—presented whole new avenues of exploration.

Neutrinos are useful messengers because of their tiny mass and lack of charge, which enable them to pass through normal matter relatively unimpeded. These phantom particles can be used as probes to study distant events such as supernovae, the explosions that end the lives of highly massive stars. In this instance, the only particle that is able to escape the extremely dense and energetic nature of such a collapse is the neutrino.

But it was not until 1987 that the concept of multimessenger astrophysics was born. At that time experiments deep underground detected a steady stream of neutrinos coming from the Sun. Shortly after that a burst of neutrinos was detected from a supernova in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way. Establishing the direction and location of these events gave astrophysicists the first correlation of two messenger particles—neutrinos and photons—and the promise of searching for other messengers that could be expected to be produced in such transient events, including high energy neutrons and disturbances in the fabric of spacetime, known as gravitational waves.

Penn State and the members of the AMON research consortium are engaged in a unique global collaboration, sharing resources, expertise, and data in multimessenger detection. The IceCube Observatory in Antarctica is detecting neutrinos with instruments buried deep in the ice over a broad (1 cubic kilometer) volume. In the Mediterranean Sea at the ANTARES observatory, neutrino detection is occurring deep within the sea. High energy cosmic rays are being picked up at the Auger Observatory in the plains of Argentina. Gravitational waves are the still-elusive quarry sought by the LIGO observatories in Washington State and Louisiana, and the Virgo observatory in Italy. And high energy gamma rays continue to be detected at multiple facilities, like the HAWC Observatory in Mexico and the Swift and Fermi Observatories in space.

AMON takes advantage of the ability of "triggering" telescopes at these and other observatories to collect data from broad swatches of sky (noted above) and quickly share it within the network so that a rapid response with narrow-field "follow-up" telescopes can map the event in time and space. Data collected from all the "subtle messengers" combined will greatly increase the probability of observing phenomena that have never been observed before.

"AMON serves as the connective tissue—the network that stitches these global partners together," says Derek Fox, associate professor of astronomy and astrophysics and science coordinator for the consortium. Penn State has unique advantages that make it an ideal hub for the AMON project.

The Research Computing and Cyberinfrastructure (RCC) unit of Information Technology Services enable scholars to do large-scale computations through linked services, including hardware, software, and personnel.

The High Performance Computing (HPC) system within RCC is a shared resource among dozens of researchers in a host of departmental and interdisciplinary units at Penn State that meets the dual data challenges presented by the AMON project. First, there is the need to continuously receive data from the triggering instruments. This requires computing systems with robust and consistently high "up-time." The HPC has sub-systems rated at Tier III, with 99.999 percent up-time (less than five minutes of downtime annually).

The second challenge is the need for vast amounts of computing power in "bursts" of time that can run rapid simulations on received probable coincidence data and quickly send "alerts" to narrow field-of-view follow-up instruments for confirmation. HPC has the flexibility to deliver those bursts of CPU power.

"This resource is very attractive to researchers collecting complex data," explains Doug Cowen, professor of physics and astronomy and astrophysics and a researcher with AMON and the IceCube neutrino observatory. "We are experimenting with a 'probabilistic' database that can collect disparate data, say, on neutrinos and gamma rays, and quickly determine the probability that both have come from the same source. This is cutting edge database work."

Because of the efficiency of the HPC systems the Penn State IceCube group has been able to process and rapidly deliver much more simulation data that any other similarly sized group.

Human and technical challenges remain. Getting thousands of scientists together to communicate openly across many different languages and cultures is one of the biggest. As Smith explains, "We need to build trust between the participating observatories, and this is a big part of the effort. We are asking them to share their most precious commodity—their data. Yet there is recognition among these diverse groups of scientists that only through cooperation and collaboration are we going to see the breakthroughs we seek in understanding the universe. There is a lot of incentive to work together.

"Economically, it also makes sense to create a hub at one location where information is collected and sent to all the partners, rather than going through individual relationships between each observatory," he adds. "This is a strategy of data sharing that is likely to become more common as scientists grapple with the increasingly complex data that needs to be analyzed."

"We are truly at the dawning of the age of multimessenger astronomy," adds Fox. We expect to see discoveries that will be revolutionary for our understanding of the universe, including being able to detect some of the most violent and dramatic phenomena."

Miles Smith, Ph.D., is a research associate in the Institute of Gravitation and the Cosmos in the Department of Physics and director of operations for AMON. Doug Cowen, Ph.D., is professor of physics and astronomy and astrophysics and a researcher with AMON and the IceCube neutrino observatory. Derek Fox, Ph.D., is associate professor of astronomy and astrophysics and science coordinator for AMON.

Other Penn State researchers involved in AMON include Paul Sommers, Stephane Coutu, Gordana Tesic (Physics); Peter Meszaros, Josh Fixelle (Astronomy); Jogesh Babu (Statistics), and Prasenjit Mitra (Information Science and Technology). Abhay Ashtekar (Physics) and Padma Raghavan (Computer Science and Engineering) have been active in securing funding for the project.

Funding for the initial development of AMON has come from the Office of the Vice President for Research and the Eberly College of Science.