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1 Report of the Panel on High-Energy Astrophysics from Space
Pages 17-64

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From page 17...
... l Report of the Panel on -gh-~ner~ Astrophysics from Space H
From page 18...
... Still, dramatic discoveries of cosmological gamma-ray bursts, magnetars, baryon-rich clusters of galaxies, iron lines from accretion disks, and microquasars have led to a better understanding of these energetic environments and have taken us closer to a number of long-range scientific quests: finding the first light of the modern universe, elucidating relativistic gravity by directly imaging black holes, and understanding the origin of the elements that are critical for forming planets and life. The technological capability is at hand to take the next steps toward these goals.
From page 19...
... Such a program would do three things: · Lay the foundation for ultimately resolving black holes using x-ray interferometry in space. · Develop the mirror and detector technology required to create a 10-m-diameter, focusing x-ray telescope that can detect emission from the first galaxies and stars in the universe.
From page 20...
... From the almost-perfect microwave background radiation to immense clusters of galaxies; from the first quasars to the sleeping, giant black holes that they leave behind; from dense hydrogen gas clouds, where stars and their scalding planets are discreetly born, to the life-giving elements that these stars spawn we have discovered worlds more wondrous than our boldest prophecies and more subtle than our most careful predictions. This flow of enduring discovery has been sustained by applying ingenious technology to increasingly sensitive telescopes operating throughout the electromagnetic spectrum as well as by exploring the universe using cosmic rays, neutrinos, and soon, it is hoped gravitational radiation.
From page 21...
... However, even if this endeavor is brilliantly successful, it will not tell us how, when, or where the first stars and galaxies formed. Indeed, we still do not know if the first luminous objects are stars in developing dwarf galaxies, as most theory predicts, stars in normal galaxies like our own, or accreting black holes in galactic nuclei.
From page 22...
... Form an indirect image of the Gravity Power, Black Holes and Neutron Stars flow of gas around a black hole (Con-X) , Cosmic Rays (GLAST)
From page 23...
... , MeV Spectroscopy Mission, Nuclear Line X-ray Spectroscopy, Soft X-ray Surveys for three reasons. First, we do not understand how the distribution of luminous galaxies relates to that of the dark matter.
From page 24...
... However, numerical simulations suggest that the temperature ought to be closer to a few million kelvin, which is well suited to x-ray observation. Therefore, in order to describe most of the matter in the expanding universe, we need to detect local intergalactic gas and measure its density and temperature (B)
From page 25...
... This is our second quest. Black holes were predicted to swallow their gas via accretion disks, 25
From page 26...
... Infrared observations have demonstrated that there is a 2.6-million-solar-mass black hole at the dynamical center of our galaxy. This massive black hole accretes gas from its surroundings and heats it to x-ray-emitting temperatures.
From page 27...
... In addition to disks, many accreting black holes form a pair of jets that appear to flow with speeds close to that of light along opposite directions that are perpendicular to the disk (Figure 1.31. These jets were first found associated with galactic nuclei using radio astronomy.
From page 29...
... This is a second area where there are thought to be unusually good opportunities for close collaboration between observers, theorists, and laboratory astrophysicists, particularly in exploring the behavior of ultrarelativistic plasma. Neutron stars are also relativistic objects, and they permit quantitative tests of strong gravity.
From page 30...
... Several point x-ray sources, probably neutron stars and black holes that accrete gas from their companion stars, can also be discerned. Jets like those in CentaurusA are called blazers when they are pointed toward us and are also prodigious gammaray sources.
From page 31...
... All neutron stars spin, and in contrast to black holes this spin causes regular pulsations with periods that can be as short as ~ 1.5 ms. Most neutron stars are isolated and powered by their spin energy, so they slow down with time.
From page 32...
... We can also consider the global properties of AGN to understand how they operate on the average. By measuring the masses of black holes in nearby galactic nuclei, it is possible to estimate how much radiant energy was produced in forming them.
From page 33...
... . This connects strongly to our first quest, which involved understanding the role of massive black holes in the birth and evolution of galaxies.
From page 34...
... The bottom right image is of the famous Hubble Deep Field (HDF) North as observed at optical and x-ray wavelengths.
From page 35...
... , and one appears to lie in the outer parts of a nearby spiral galaxy. Some AGN are seen only through their penetrating high-energy x rays, suggesting that optical, ultraviolet, and low-energy xray photons are absorbed by gas and dust.
From page 36...
... , where the explosion is preceded by gravitational collapse and a neutron star or black hole is left behind, and those of type Ia, where there is a thermonuclear explosion of a white dwarf and no remnant. For both classes, the sudden release of energy raises the temperature to the point where violent nuclear reactions occur.
From page 37...
... Many of these lines have already been measured and, to some extent, mapped, using ASCA. However, neither the sensitivity nor the angular resolution 37 FIGURE 1.6 On the left is a Chandra x-ray image of a nearby supernova remnant, ED 102-72.3, using an emission line created by ionized neon in the hot gas formed by the explosion.
From page 38...
... . A very good example is provided by the well-studied supernova remnant Cassiopeia A, which now appears to contain a compact object, either a neutron star or a black hole.
From page 39...
... and microchannel plate detectors, it has over a hundred times better sensitivity than the Einstein Observatory, which was launched in 1978, and 10 times the angular resolution of ROSAT. It also has a strong spectroscopic capability using transmission gratings and will provide energy resolution of up to one part in a thousand (depending upon the energy)
From page 40...
... The x rays are produced by hot gas in a corona. The moderate-resolution spectrum measured using the Advanced CCD Imaging Spectrometer shows several broad features; those in the ~ 1- to 2-keV interval are contributed mainly by Si and Mg.
From page 41...
... at the expense of angular resolution (15 arcsec) , the European-led XMM-Newton3 (launched in December 1999)
From page 42...
... PROPOSED MANOR MISSION: CONSTELLATION-X MISSION DEFINITION Con-X7 (Figure 1.8) is planned as a high-throughput, x-ray facility emphasizing observations with unprecedented energy resolution, E/DE, of between about 300 and 5000 over a broad energy range, ~0.25 to 6See .
From page 43...
... G LAST and EXIST will both operate in low Earth orbit. Courtesy of NASA/Goddard Space Flight Center (GSFC)
From page 45...
... If, as numerical simulations strongly suggest, most of the mass of the intergalactic medium is now at million-kelvin temperatures, then Con-X should be able to measure its distribution and follow its dynamics by seeing absorption lines (notably those formed by oxygen ions) in the spectra of hundreds of bright, background quasars in much the same way that optical astronomers have been able to detect 30,000-K intergalactic gas from when the universe was only a few billion years old using hydrogen and carbon atoms (Figure 1.91.
From page 46...
... Detecting these elements, and their ionization states, soon after they are formed will serve as a quantitative test of our understanding of how radiation escapes from these remnants as well as of the theory of nucleosynthesis inside supernova explosions. The most abundant elements can be assayed from supernovae occurring as far away as the Virgo cluster, which should be sufficient to derive a fair average rate of element production.
From page 48...
... In this way it should be possible to inferthe physical conditions in the source. Con-X should be able to perform timeresolved spectroscopy of the inner regions of accretion disks orbiting massive black holes and to form indirect "imaging" ofthe gas flow.
From page 49...
... In another approach, it will be possible to infer whether or not our own galactic center, which is currently dormant, was active over the past few centuries by observing the x-ray photons scattered back towards us by more distant molecular gas. Analogous accretion disk studies will be possible for the stellar black holes.
From page 50...
... Images of bright, extended sources should have angular resolution of ~10 arcmin. Bright point sources can be located to 30 arcsec, which should allow the identification of some of the large number of sources that could not be located from EGRET observations.
From page 51...
... PANEL ON HIGH-ENERGY ASTROPHYSICS FROM SPACE Virgo Region (Em, ~ 1 GeV )
From page 52...
... Answering these questions should lead to a much better understanding of how jets are powered at their sources, especially whether this is due to spin of the black hole or the energy liberated by the accreting gas. Furthermore, by determining the evolution of the strengths of these jets over cosmic time, it should also be possible to check whether or not they dominate the gamma-ray background, as is widely suspected.
From page 53...
... GLAST seems to be a particularly good candidate to produce the key insight that will identify the predominant source of GRBs. Above a certain energy, gamma rays from GRBs and blazers are also subject to absorption outside their sources as they propagate through the infrared cosmological background radiation.
From page 54...
... (This is a particularly important feature because the hard x-ray sky is so variable and is enabled by having eight telescopes.) The final survey limit would be roughly 100 to 1000 times fainter than the HEAD-1 limit and roughly 10 times fainter than the anticipated Swift hard x-ray survey (with a much broader energy range and superior angular resolution)
From page 55...
... In addition, it will be possible to observe QPOs from the disk coronas around neutron stars and stellar black holes at the high energies where they are most prominent.
From page 56...
... MAXI M (E, F) The second quest, imaging a black hole, could succeed, in principle, using x-ray interferometry, as proposed for MAXIMS (Figure 1.133.
From page 57...
... These mirrors reflect the x rays onto a second spacecraft up to 1000 km away, where the interference fringes are formed. One possible intermediate goal is a pathfinder mission designed to demonstrate ~ 100 ,uarcsec resolution at ~ 1 keV, comparable to what is achieved at radio wavelengths using very long baseline interferometry (VLBI)
From page 58...
... Largeformat detectors capable of sub-eV energy resolution will also be necessary. A paced program of mirror and detector technology development directed toward these long-term goals is recommended.
From page 59...
... Continuous monitoring of large numbers of these sources at low and intermediate x-ray energies will complement the high-energy studies proposed above using EXIST and help produce an indirect image of accretion disks and their coronas. Continuous monitoring of a large 59
From page 60...
... Hard x-ray and gamma-ray missions were successfully mounted from the Southern Hemisphere and were able to confirm directly the production of radioactive nuclei within the expanding supernova remnant. Since that time the capabilities of balloons have increased considerably.
From page 61...
... Black holes, neutron stars, cosmological GRBs and relativistic blast waves, supernova nucleosynthesis, gamma-ray jets, cosmic-ray acceleration in supernova remnants, and the hot intergalactic medium were all widely discussed in the theoretical literature before observations established their reality. However, what was found was not usually exactly what had been predicted, so the theory had to be modified.
From page 62...
... Black holes, supernovae, and gamma-ray bursts have captured the public imagination like few other topics in the physical sciences and are at least as firmly established as cosmology and the search for extraterrestrial life. High-energy astrophysicists have experimented successfully with a variety of new education and outreach initiatives, including the HighEnergy Astrophysics Learning Center and the Astronomy Picture of the Day.
From page 63...
... HST Hubble Space Telescope INTEGRAL International Gamma-Ray Astrophysics Laboratory ISS International Space Station LISA Laser Interferometer Space Antenna MAXIM Microarcsecond X-ray Imaging Mission MO&'DA mission operations and data analysis (NASA) NASA National Aeronautics and Space Administration NGST Next Generation Space Telescope NSF National Science Foundation OSS Office of Space Science (NASA)
From page 64...
... RXTE Rossi X-ray Timing Explorer SAG Smithsonian Astrophysical Observatory SIM Space Interferometry Mission STScI Space Telescope Science Institute ULDB ultralong-duration balloon VERITAS Very Energetic Radiation Imaging Telescope Array System VLBI very long baseline interferometry XMM-Newton X-ray Multi-Mirror Observatory, a European collaboration x-ray space mission


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