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3 Report of the Panel on Particle, Nuclear, and Gravitational-Wave Astrophysics
Pages 123-166

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From page 123...
... J Report of the Panel on Panicle Nuclear an] Grav~bona~ - Wave Astrophysics
From page 124...
... The Panel on Particle, Nuclear, and Gravitational-Wave Astrophysics of the Astronomy and Astrophysics Survey Committee recommends that highest priority be given to the Laser Interferometer Space Antenna (LISA) because of the fundamental and novel exploration of the gravitational-wave universe it can accomplish, including the observation of massive black holes coalescing in colliding galaxies and the study of white dwarf binaries in our own galaxy.
From page 125...
... SCIENCE OPPORTUNITIES A unifying theme of many of the projects considered by this panel is the desire to study energetic processes in the cosmos not only in all wavelength ranges but with a variety of signal carriers. The idea would be to detect gravitational waves, neutrinos, hadrons, and photons from the same source and so take advantage of the complementary information they carry: · Gravitational waves provide information on the bulk motions of matter in the most energetic events in nature, such as the coalescence of black holes.
From page 126...
... Periodic gravitational waves may originate in the coalescence of massive black holes, in the accretiondriven excitation of normal modes in neutron stars, or in the rotation of pulsars. A stochastic background of gravitational waves would result from a collection of spectrally unresolved binary stellar systems and possibly from the metric fluctuations in the primeval universe.
From page 127...
... By extending the search to cosmological distances, the improvements to the long-baseline detectors on Earth will make it likely that coalescing binary neutron stars will be detected. Lowering the frequency sensitivity of gravitational-wave detectors would open the window on an important new class of sources involving the formation and interaction of ~ 106-solar-mass black holes, which are thought to lie at the centers of many galaxies.
From page 128...
... Finally, the possibility is discussed of opening a new window on particle acceleration by detecting high-energy neutrinos produced deep inside energetic astrophysical sources. HAM MA- RAY ASTRO P HYS j C S The study of very-high-energy gamma rays is a powerful tool for understanding particle acceleration in energetic astrophysical sources in distant galaxies as well as in the Milky Way.
From page 129...
... The most important instrumental innovation for the coming decade will be stereoscopic imaging Cherenkov telescopes with greatly improved sensitivity and angular resolution. In addition to the new directions outlined above, the next-generation Cherenkov telescopes have the potential to address other exciting topics, including (1)
From page 130...
... It is widely suspected that the bulk of cosmic rays are accelerated by diffusive shock acceleration, but the evidence for this hypothesis is somewhat indirect because cosmic-ray energy spectra measured in the Galaxy (oCE-2 7) are apparently modified from the accelerated spectra (expected to be oCE-2 i)
From page 131...
... NASA's proposed Interstellar Probe mission, which would send a spacecraft beyond 200 AU, would make a broad range of measurements of matter and fields in interstellar space. As an in situ investigation, it is outside the purview of the Astronomy and Astrophysics Survey Committee, but it is mentioned here because it would include measurements of the spectra and composition of cosmic rays in the local interstellar medium (ISM)
From page 132...
... At 50 kilotons the detector is big enough to detect copious solar and atmospheric neutrinos but not the high-energy neutrinos that might be tracers of acceleration processes in distant astrophysical sources. To achieve this goal, it is believed that detector volumes on a scale of at least a cubic kilometer (1000 megatons of water)
From page 133...
... The highlights of the past decade include the first real-time, directional detection of solar neutrinos in the Kamiokande and SuperKamiokande light-water detectors; the confirmation by these detectors that the flux of neutrinos is much lower than stellar evolution calculations predict; the study of systematic errors in the pioneering 37Cl experiment, putting the experiment on a more stable foundation; and the remarkable suppression of the low-energy neutrinos observed in two calibrated 7iGa detectors, GALLEX and SAGE. In addition, a series of helioseismological measurements confirms that the temperature and density profile of the Sun are essentially as predicted by stellar-structure calculations.
From page 134...
... Completion of the solar neutrino program will require a further series of experiments that can map the solar neutrino energy spectrum, including the low-energy pp neutrinos, separately in electron neutrinos and in all types of neutrinos. Comparison of the two series of experiments will permit the mixing of neutrinos to be measured as a function of energy.
From page 135...
... N U C HEAR ASTRO P HYS j C S The cosmos is powered by gravity and by nuclear reactions. Much of what is understood about processes in the universe is learned through the study of nuclear physics and nuclear astrophysics.
From page 136...
... Thus we may learn about the equation of state of cold, dense nuclear matter from these astrophysical processes in a way that is complementary to the way we learn from collisions of relativistic heavy ions.
From page 137...
... . Interpretation of recent data on atmospheric and solar neutrinos in terms of oscillations suggests that neutrinos have a small mass, but it is unlikely that such an interpretation provides the full explanation for dark matter because it alone cannot explain structure formation.
From page 138...
... Their annihilation products could be detected by properly designed deep neutrino detectors. Finally, WIMP annihilation would also produce an anomalous flux of antiparticles that might be detected by particle detectors in space.
From page 139...
... GALACTIC COSMIC RAYS Direct measurements of the primary cosmic radiation made with detectors carried above the atmosphere by balloons and spacecraft now extend to energies of about 10~2 to 10~4 eV. Information at the top end of this range comes from balloon-borne emulsion chamber experiments and is limited to H
From page 140...
... HIGHEST-ENERGY COSMIC RAYS Japan's Akeno Giant Air Shower Array (AGASA) uses measurements of ground-level particle densities in shower cascades to infer the primaryparticle energy and arrival direction.
From page 141...
... S O MAR N EUTR. N O S The second generation of solar neutrino experiments includes the Super-Kamiokande light-water Cherenkov detector, the Sudbury Neutrino Observatory (SNO)
From page 142...
... RECOMMENDED NEW INITIATIVES The panel was able to identify several key challenges that are ripe for progress at this time: i] · To detect gravitational radiation from interacting massive objects, ncluding massive black holes; · To understand the origin of gamma rays of very high energy from sources such as AGN and SNRs; · To identify positively the sources of galactic cosmic rays and to measure the output of these cosmic accelerators; · To identify the nature and distribution of the bulk of the matter in the universe; · To understand the origin of the highest-energy particles in nature;
From page 143...
... It is hoped that LISA will be put forward as a joint mission for launch before the end of the first decade of this new century. LISA should observe, for the first time, the coalescence of supermassive black holes as distant galaxies merge.
From page 144...
... on a reference mass used to guide the motion of the spacecraft containing the optical components. The concept of surrounding a reference mass by a spacecraft shell that follows its motion and shields it from nongravitational forces was tested in the TRIAD program almost two decades ago at acceleration levels approximately 107 times greater than needed for LISA.
From page 145...
... It also has the potential to survey the Milky Way for binary systems involving white dwarfs, neutron stars, and stellar mass black holes. Courtesy of W
From page 146...
... In a stereoscopic configuration, where each air shower is viewed by multiple cameras, VERITAS achieves its best sensitivity (more than an order of magnitude improvement over existing instruments; see Figure 3.3) and its optimal energy and angular resolution (better than existing instruments by a factor of between 2 and 33.
From page 147...
... For distant sources, spectral cutoffs that are correlated with redshift will provide important information about the cosmic IR background radiation. An important theory challenge posed for VERITAS is to understand the origin and characteristics of the energetic signals from AGN and GRBs, including acceleration mechanisms, the relative importance of electrons and ions, and spectral shapes and cutoffs.
From page 148...
... TeV energies are well suited for detection of this emission, owing to the lower Galactic diffuse background and superior angular resolution of VERITAS relative to satellite-borne instruments. VERITAS should enlarge the sample of VHE pulsar nebulae by a factor of 3 or 4 and should map the emission from strong sources such as the Crab; it would, as well, provide a unique test of pulsar wind models.
From page 149...
... Further studies of solar neutrinos will be necessary to understand fully the properties of neutrinos and their role in astrophysical processes. More iThe estimated cost for VERITAS that appears in the survey committee report includes grants and operations in addition to instrumentation, as described in this report's preface.
From page 150...
... A theory challenge posed by ACCESS is to identify signatures that discriminate among models of the origin of the most energetic galactic cosmic rays. In the supernova picture, for example, this would require relating a realistic and detailed distribution of various supernova types, including characteristic spectra of particles that they accelerate, to elemental composition at PeV energies as observed locally after propagation in the galaxy.
From page 151...
... It is technologically ready and constitutes an obvious next step in the exploration of high-energy cosmic rays. Moreover, it has the potential to change the paradigm for the origin of Galactic cosmic rays if the source spectrum is significantly steeper than expected in the model of first-order diffusive shock acceleration by supernova blast waves.
From page 152...
... ) \ \ \ / \ \ 20 20.5 FIGURE 3.6 The spectrum ofthe highest-energy cosmic rays as reported by the AGASA experiment.
From page 153...
... A good understanding of the composition of cosmic rays is critical to unraveling the acceleration mechanism. For example, in a top-down process like the decay of topological defects, a large gamma/hadron ratio is expected, in contrast to the proton flux expected from AGN.
From page 154...
... A few dramatic neutrino events correlated with ORB observations would provide strong evidence that these spectacular objects are the sources of the highest-energy cosmic rays. The IceCube proposal for a kilometer-scale neutrino detector is designed to expand significantly the reach of high-energy neutrino telescopes.
From page 155...
... S O EAR N EUTRi N OS A third generation of solar neutrino experiments will be required to complete the program for measuring the energy spectrum and flux of solar neutrinos. The goal is to make a complete set of precise measurements of neutrinos from an astrophysical source.
From page 156...
... The display here depicts a large electromagnetic cascade initiated by an electron neutrino interacting nearthe center ofthe detector. A high-energy muon neutrino would appear as an elongated series of hits along the path of a highenergy muon produced when the neutrino interacts, either inside the detector or in the surrounding ice.
From page 157...
... The solar neutrino experiments will lead to an understanding of the emission spectrum of neutrinos by the Sun and the fundamental physics of neutrinos. Without this knowledge, it is not possible to make progress in other areas of astrophysics where neutrinos play an important role.
From page 158...
... 1 Figure 9 it_ ..
From page 159...
... thrive, the astronomy and astrophysics and physics communities and the funding agencies must work to overcome these boundaries and focus on using multiple approaches to solve diverse but interconnected scientific problems. The frontiers of particle and nuclear astrophysics, whether in space, on the ground, or underground, should be viewed as essential tools for answering fundamental questions of physics as well as astrophysics.
From page 160...
... Hopkins in Arizona for atmospheric Cherenkov telescopes, and the Amundsen-Scott South Pole Station for the proposed IceCube detector. NASA is currently developing an Ultralong Duration Ballooning (ULDB)
From page 161...
... Indeed, much of the evidence for physics beyond the standard model comes from particle astrophysics and cosmology, including evidence for neutrino masses from solar and atmospheric neutrinos; evidence for baryonnumber violation and CP violation from the baryon asymmetry of the universe; cosmological evidence for a nonzero cosmological constant; and indications for a new physics at an ultrahigh-energy scale associated with inflation in the very early universe. Investigations such as the search for dark matter and solar neutrino experiments address fundamental physics problems, from supersymmetry to the origin of mass.
From page 162...
... The NASA concept of missions is probably well suited to the large experiments being considered in particle and nuclear astrophysics: experiments should be of fixed duration, and their costing should include operations and the extraction of science. Various approaches to an important science theme could be coordinated by an organization set up for a fixed time.
From page 163...
... AGASA Akeno Giant Air Shower Array (Japan) AGN active galactic nuclei AMANDA Antarctic Muon and Neutrino Detector Array AMS Alpha Magnetic Spectrometer ANL Argonne National Laboratory (DOE)
From page 164...
... GLAST Gamma-ray Large Area Space Telescope, a NASA-DOE mission GRBs gamma-ray bursts GZK cutoff upper limit to the cosmic-ray energy spectrum of around 1019 eV as specified by the theory of Greisen, Zatsepin, and Kuz'min HEGRA High-energy Gamma Ray Astronomy experiment, a project that features a gamma-ray telescope in La Palma, Spain HELLAZ proposed French solar neutrino detector HERON a solar neutrino detector using superfluid helium HESS High-Energy Stereoscopic System; gamma-ray telescope in Namibia HiRes High-Resolution Fly's Eye IR infrared ISM interstellar medium ISS International Space Station LANL Los Alamos National Laboratory (DOE) LBNL La~vrence Berkeley National Laboratory (DOE)
From page 165...
... , a detector for atmospheric neutrinos and magnetic monopoles MAGIC gamma-ray telescope in La Palma, Spain MILAGRO large, water Cherenkov detector at Los Alamos, New Mexico Mir space station of the Russian Federation MPS Division of Mathematics and Physical Sciences (National Science Foundation) MSU Michigan State University NASA National Aeronautics and Space Administration NEMO Neutrino Mediterranean Observatory, an international collaboration to study double-beta decay without the emission of neutrinos NESTOR Neutrino Experimental Submarine Telescope with Oceanographic Research; a deep-sea neutrino-detector in the Mediterranean NSF National Science Foundation OGLE Optical Gravitational Lensing Experiment, a program to search for dark, unseen matter using the microlensing phenomena ORNL Oak Ridge National Laboratory (DOE)
From page 166...
... TAMA a 300-m laser-interferometer gravitational-wave antenna (Japan) TREK detector aboard Mir that probes the composition of the galactic cosmic rays TRIAD Tucson Revised Index of Asteroid Data UHE ultrahigh-energy ULDB ultralong-duration ballooning VERITAS Very Energetic Radiation Imaging Telescope Array System VHE very high energy VIRGO French-Italian gravitational-wave interferometry project WIMP weakly interactive massive particles


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