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Pierre Auger Observatory

The Pierre Auger Observatory is the world's largest cosmic-ray detector, aimed at the study of the most energetic particles in the Universe. These are extremely rare particles with energies from 1018eV to 1020eV and beyond (a billion to a trillion times the energy stored in the mass of a proton). How Nature accelerates particles to such enormous energies is still a mystery. To detect them with good statistical precision, physicists from 17 countries are deploying 1600 detectors (water Cherenkov counters) over a 3000km2 area of Western Mendoza Province, Argentina, as well as 24 nitrogen fluorescence telescopes that look at the sky over the large ground array on dark, moonless nights. Another similar array of detectors is planned for deployment in Colorado. Penn State faculty Stephane Coutu and Paul Sommers are involved in the project, with Sommers serving as Co-Spokesman of the international Auger Collaboration. For more information, see the official Auger Web site. You can also explore the Auger Observatory using Google Earth.




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Welcome to the Center for Particle and Gravitational Astrophysics!

The Center for Particle and Gravitational Astrophysics is engaged in a bold synergistic approach to understanding high energy processes in the universe. Our faculty at Penn State are prominent participants seven major international projects which make observations using extremely high energy protons and nuclei, neutrinos, gamma-rays, X-rays and gravitational waves. These projects are, respectively, the Pierre Auger Cosmic Ray Observatory, the IceCube Neutrino Observatory, the Swift Gamma-Ray Burst Explorer satellite, the Chandra X-ray Observatory, the XMM-Newton X-ray Observatory, the Laser Interferometric Gravitational Wave Observatory (LIGO) and the North American Nanohertz Observatory for Gravitational-waves (NANOGrav).

Our faculty are also involved in developing future facilities such as the International X-ray Observatory, the Large Synoptic Survey Telescope (LSST) and the Joint Astrophysics Nascent Universe Satellite (JANUS). Two projects in TeV gamma ray astronomy are the High Altitude Water Cherenkov (HAWC) observatory and the Advanced Gamma-ray Imaging System (AGIS). There is also ongoing work with the Fermi satellite, the VERITAS high energy gamma ray observatory, the Cosmic Ray Energetics and Mass (CREAM), the Cosmic Ray Electron Synchrotron Telescope (CREST) high-altitude balloon, and in the former Laser Interferometer Space Antenna (LISA) project, now called NGO.

Penn State is the only U.S. institution participating in both Auger and IceCube, the premier ground-based projects of high energy particle astrophysics. Potentially observable sources for both Auger and IceCube include super-massive black holes at the center of active galaxies, and the explosive phenomena that give rise to gamma ray bursts (GRBs). Some GRBs are believed to be especially violent supernova explosions, while others are probably mergers of collapsed stars in binary systems.

The Swift GRB Explorer satellite is presently providing the best gamma ray and X-ray observations of GRB explosions. Swift has been successfully operating for a number of years, its mission control center being at Penn State. Chandra and XMM have been successfully operating for over a decade and are leading to substantial advances in understanding the demography, physics, and ecology of supermassive and stellar mas black holes, active galaxies and supernovae. LIGO is undergoing a major upgrade towards achieving its ultimate sensitivity.

Commensurate with these significant experimental efforts, Penn State also plays a leading role in the theoretical and numerical modeling of fundamental high energy interactions as well as astrophysical phenomena such as black holes, gamma-ray bursts, the high energy Universe and the formation of the first objects and large scale structures in the Universe.

GRBs, and the mergers of super-massive black holes in the cores of galaxies and quasars are also likely sources of detectable gravitational waves. Our Center will be studying GRBs and active galaxies by observing strong-interaction protons and nuclei, weak-interaction neutrinos, electromagnetic radiation, and gravitational waves. Together we cover all four forces of nature. We have initiated a specific multi-messenger observational program called the Astrophysical Multimessenger Observatory Network (AMON), which aims to utilize all four forces to detect sub-threshold signals from the above described cosmic sources. This multi-force approach to high energy astrophysics is a pioneering venture in which the one-dimensional electromagnetic spectrum of conventional astronomy is supplemented with three other windows to the Universe. The discovery potential is enormous.

Together with the Center for Fundamental Theory, the Center for Theoretical and Observational Cosmology and the Institute for Gravitation and the Cosmos, the synergy between our various specialties and the breadth of knowledge to be gained through collaborations provide exciting prospects for making breakthroughs in our understanding of the Cosmos.


  • The Institute for Gravitation and the Cosmos will host the second Astrophysical Multimessenger Observatory Network (AMON) Workshop on October 24-26, 2013. For more information, please visit
  • The Center for Particle and Gravitational Astrophysics will hold a focus session from April 12 through 14 to develop detailed plans for the next phase of the Pierre Auger Observatory. It will bring together Auger leaders from Europe, South America and the U.S. It will be followed on April 15, 2013 by a special colloquium, honoring Paul Sommers, by Ralph Engel entitled "Highest Energy Cosmic Rays-First Answers and New Puzzles." All events will be held in 320 Whitmore.
  • CPA Journal Club members meet to discuss current literature in particle astrophysics each Friday at 12:30 p.m. in 318 Osmond Lab.
  • Tyler Anderson, a graduate student of Stephane Coutu, has been awarded a three-year NASA Earth and Space Science Fellowship. He was chosen as one of ten recipients from a pool of 88 applicants.
  • D.F. Cowen, T. DeYoung, M.M. Foerster, B.D. Fox, C. Ha, D.J. Koskinen, S. Lafebre, M.J. Larson, P. Meszaros, M. Prikockis, D. Rutledge, A. Slipak, G. Stephens, and P.A. Toale are co-authors of "Limits on Neutrino Emission from Gamma-Ray Bursts with the 40 String IceCube Detector", an important paper published in PRL which was also featured in Nature. arXiv:1101.1448

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