Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session G4: New Eyes on the Universe I |
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Sponsoring Units: DAP Chair: Steven Barwick, University of California, Irvine Room: Plaza F |
Sunday, May 3, 2009 8:30AM - 9:06AM |
G4.00001: New Results from the Pierre Auger Observatory Invited Speaker: The Pierre Auger Observatory in Malargue, Argentina, is the world's largest detector for the study of the origin of ultrahigh energy cosmic rays. The experiment stretches over $3000\,\mathrm{km}^2$ and measures cosmic rays with energies above $10^{18}$\,eV using two complementary detector types: an array of 1600 particle detectors on the ground, and 4 fluorescence detectors overlooking the ground array from the periphery. The Observatory is now complete, and scientific data taking started already at the beginning of 2004. Among the first results is the confirmation of the so-called GZK suppression of the cosmic ray flux at the highest energies caused by the interaction of cosmic rays with the microwave background. I will review the most recent results with a special emphasis on the energy spectrum, the chemical composition of the cosmic ray flux, and the arrival direction of the highest energy cosmic rays and their possible correlation with known astrophysical sources. [Preview Abstract] |
Sunday, May 3, 2009 9:06AM - 9:42AM |
G4.00002: TIGER: Progress in Determining the Sources of Galactic Cosmic Rays Invited Speaker: The Trans-Iron Galactic Element Recorder (TIGER) is a 1-square-meter detector system composed of scintillators, Cherenkov detectors, and scintillating optical fibers, which gives excellent resolution of individual elements in the cosmic rays. With two high-altitude balloon flights over Antarctica, TIGER accumulated fifty days of data on the elemental composition of the rare galactic cosmic rays heavier than Ni, measuring the abundances of Cu, Zn, Ga, Ge, Se, and Sr, as well as the more abundant lighter elements. After accounting for fragmentation of cosmic rays as they propagate through the Galaxy and the atmosphere above the detector system, the source material appears to be a mixture of about 80{\%} ``standard'' Solar-System composition and 20{\%} ejecta from massive stars. This mixture supports a model of cosmic-ray origin in OB associations, as has previously been inferred from the isotopic composition of the more abundant elements, Ni and lighter. These TIGER data also support a cosmic-ray acceleration model in which elements present in interstellar grains are accelerated preferentially compared with those found in interstellar gas. This emerging model of cosmic-ray origin and acceleration will be further tested with a similar but much larger instrument that will give much better statistics, improve the precision of TIGER'S studies and allowing more rare elements to be studied; Super-TIGER development is beginning now, leading to its first balloon flight in December 2012. The TIGER investigation is a collaboration among scientists at Washington University in St. Louis, NASA Goddard Space Flight Center, California Institute of Technology, Jet Propulsion Laboratory, and University of Minnesota. Principal funding for this research was from NASA under grant NNG05WC04G. We also acknowledge the excellent work of the staff of the Columbia Scientific Balloon Facility, the NASA Balloon Program Office, and the NSF Office of Polar Programs. [Preview Abstract] |
Sunday, May 3, 2009 9:42AM - 10:18AM |
G4.00003: Recent Progress and New Puzzles in Cosmic Ray Physics Invited Speaker: New exciting cosmic ray data have been reported during the last two years. One of the most interesting ones was the report of the Auger collaboration on the correlation with nearby AGN at distances less than 70 Mpc. The correlation is however not seen in the Northern sky by the HiRes collaboration and many questions are asked about it most of them by the Auger collaboration itself. If confirmed the correlation starts the era of cosmic ray astronomy. Other very interesting observations are at the beginning of the high energy cosmic ray spectrum, at energies between 10 and 1000 GeV. Unexpected anisotropy of the cosmic rays of energy above 1000 GeV was reported by the MILAGRO collaboration. The ATIC experiment presented a spectrum of the cosmic ray electrons that has a peak at about 500 GeV when the flux is multiplied by the cube of the energy. The Pamela experiment presented a positron to electron ratio increasing with energy up to 100 GeV. Both results can be interpreted as indirect detection of dark matter although there are other explanations and the two results are not fully consistent. We will discuss the importance of these results and their interpretations and will spend some time pointing at the development of new experimental techniques for cosmic ray observations. [Preview Abstract] |
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