Scientific Uses of the Space Shuttle (1974) / Chapter Skim
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HIGH-ENERGY ASTROPHYSICS
HIGH-ENERGY ASTROPHYSICS
Pages 40-82
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From page 40... ...
Recent discoveries have revolutionized astrophysical thought: the remarkable periodic and pulsed x-ray sources such as Hercules X-l, which can only be explained in terms of compact objects such as neutron stars or black holes revolving in close contact with massive stars; x rays from galaxies and from the intergalactic medium of clusters; a multicomponent diffuse, nearly isotropic background extending over the entire x- and gamma-ray range, which clearly involves the large-scale structure of the universe; gamma rays from point sources and the galactic plane; and, finally, the detection of extremely high-Z cosmic rays, extremely high-energy electrons, the isotopic composition of the lightest elements, and spectral differences of the various components. In the early period of Shuttle use the opportunity will exist to make detailed measurements of the charge and isotopic composition of cosmic rays, the fine details of the energy spectra to 10' 4 eV, and the streaming patterns of low-energy particles outside the sphere of solar influence.
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From page 41... ...
Although we envisage a range of opportunities, only a continuing program of unmanned, long-lived automated spacecraft can provide the continuity of observations required to develop the field and to ensure a succession of new discoveries. The pallet on the Shuttle sortie missions provides opportunities for short observing programs, for development and test of instruments before commitment to longterm flight, and for involvement of many participants in the program, as in the present balloon and rocket efforts.
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From page 42... ...
The presence of neutron stars and black holes in binary systems permits us to obtain a vast amount of information on the physics of highly compressed and nuclear matter. Furthermore, we can for the first time examine dynamical properties in a very intense gravitational field -- one in which general relativity effects predominate.
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From page 43... ...
In addition, the inverse Compton reaction between cosmic rays and the microwave background, which result in high-energy photons, will allow study of the extended radio regions associated with these objects. Extending the observations to earlier epochs, i.e., greater distances, would allow the study of the evolution of active galaxies.
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From page 44... ...
HIGH-SENSITIVITY SURVEYS The present limit of 10t4 Sco X-l should be extended to 10t8 Sco X-l with a survey divided into three energy ranges, -0.1-2 keV, 2-20 keV, and 20-200 keV. In at least one of these energy ranges, the surveys must have the following capability: location of point sources to 1 sec of arc, structure of extended sources to 0.1 sec of arc, and broadband spectra (X/AX~5)
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From page 45... ...
Furthermore, highenergy electrons, wherever they exist, signal their presence by emitting gamma rays via scattering of the lower-energy radiation present in the same places. This gives knowledge of the electrons independent of assumptions about the magnetic field, on which the radio emission from these electrons depends, and indirectly about the magnetic fields as well -- in supernovae, radio galaxies, galactic nuclei or jets, and intergalactic space.
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From page 46... ...
It helps in deciphering the origins of the high-energy gamma radiation that the most interesting and likely processes leave characteristic signatures on the spectrum. The interaction of cosmicray particles with gas, producing gammas by TT° decay, yields a spectrum with a broad peak at 68 MeV, tailing off gradually to a spectral slope paralleling that of the cosmic rays.
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From page 47... ...
The discovery of unexpectedly high-intensity gamma radiation along the galactic plane in the neighborhood of the galactic center, and of possible discrete sources in this region, is one of the most remarkable outcomes of balloon flights and the few small satellite observations conducted of gamma rays thus far. In order to unfold the structure of the galactic center region, as well as to resolve the other phenomena mentioned above, the energies of high-energy gamma rays must be measured well enough to distinguish differences in the broad spectral features of the different sources; it is vital to measure angles to the smallest fraction of a degree permitted by the fundamental requirement of being able to apply these measurements to extremely small fluxes (<10t7 photon cmt2 sect1 in many important cases)
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From page 48... ...
X rays and gamma rays are produced frequently in conjunction with, or by, these high-energy particles. The energy density of cosmic rays in the galaxy, ~1 eV/cm3, is comparable with that of the containing magnetic fields, of starlight, and of the kinetic motion of interstellar matter.
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From page 49... ...
Once the particles escape from the vicinity of the sources, they are contained in the microgauss galactic magnetic fields. One sees then a superposition of many sources in which the galactic cosmic rays are largely isotropic upon reaching earth.
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From page 50... ...
At low energies, because of the ionization range requirements, we are sampling very local distributions of galactic cosmic rays (e.g., the range of a 1-MeV proton in the typical galactic magnetic fields is ~ 200 pc)
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From page 51... ...
4. To measure the energy spectra and elemental and isotopic composition of solar energetic particles and solar x rays and gamma rays.
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From page 52... ...
Of the above modes, it must be emphasized that by far the most important is the free-flying, long-life observatory. Some of the subdisciplines of high-energy astrophysics have become highly developed areas of precise measurements and sophisticated technology, in which the most significant objectives require the continuity of observations and long observing times, which are properties of the free-flying mode but not of the brief sortie missions.
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From page 53... ...
Since x-ray observations can only be carried out in space, it is imperative that permanent orbiting observatories, operated as national facilities, be provided -- a requirement that can be satisfied economically only with free-flyers. In particular cases, the capability for recovery and refurbishment will decrease operating costs.
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From page 54... ...
Their gross parameters are summarized in Table 4. Instruments for the sortie pallet and for the free-flyer are designated S and FF, respectively.
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From page 55... ...
Furthermore, this sensitivity is achieved without any sacrifice in angular resolution, which should be better than 1 sec of arc. This facility has the power to attack virtually every classical problem in astronomy -- evolution of stellar systems, the structure of the galaxy, the nature of galactic nuclei, the origin and distribution of cosmic rays, the structure and evolution of clusters of galaxies, the evolution of active galaxies, or the large-scale structure of the universe.
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From page 56... ...
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From page 57... ...
i „•:§ sa ill sio l!
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From page 58... ...
The large-area arrays are conveniently constructed in modular sections of 1 to 2 sq m area and about 3-m length. The achievement of some specific objectives outlined above can be accomplished by Shuttle sortie modes (SX-1)
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From page 59... ...
studies of a large number of objects. The first requirement can conveniently be met in a Shuttle sortie mode (S X-2)
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From page 60... ...
: S X-6, FF X-7. Studies of the angular size of extended sources such as the Crab nebula, Perseus cluster, and galactic disk at various energies provide unique information on electron distributions and distinguish between regions of thermal and nonthermal emission in the same object.
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From page 61... ...
not accessible to a focusing telescope; and a specialized crystal spectroscopy instrument will have a much greater collecting area for a given weight and volume. The observation of emission lines or absorption edges will play an extremely important role in the development of our knowledge of discrete galactic x-ray sources, the interstellar medium, and extragalactic sources.
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From page 62... ...
A 1 5 percent polarization was detected with a ~ 0.3 m2 crystal during a rocket flight of ~ 300-sec duration. The detection of faint spectral features or precise determination of polarization requires extremely long observation times.
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From page 63... ...
Larger arrays or more efficient imaging schemes would be necessary to monitor sources with resolutions of 0.1 sec as necessary to observe the pulsating characteristics of x-ray pulsars and study the variations of their orbital periods. Obviously such an instrument should be considered for small free-flyers.
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From page 64... ...
The investigations characterized below and in Table 5 include some that are recommended for the sortie mode, especially in the early part of the Shuttle era. Sortie experiment designations begin with the letter S in the table, and free-flyers with FF.
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From page 65... ...
With the high sensitivity available, exceptionally high-energy gamma rays can be used in this scan of the galactic plane to obtain fine angular resolution, avoid source confusion, and thus distinguish between diffuse origins and an extensive collection of point emitters. The instrument will also obtain a thorough survey and spectral analysis of the radiation from high galactic latitudes and find out whether much of this radiation is in fact isotropic and hence of cosmological origin.
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From page 66... ...
9 ^ ^ 3 S ^ •fit ^ *
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From page 67... ...
gamma rays h- Detailed study of partici a-ray high0energy gamma-ray sources for limited tim mma0 Precise energy speetra ot with known gamma0ray ively High sensitivity measure illation ment of low0 and medi ow- and energy gamma rays fro ;y selected areas of the sk 1 c u it *
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From page 68... ...
Determination of the intensities of gamma-ray lines from such processes as radioactivity in supernova remnants, positron annihilation in the galactic disk or in extragalactic interactions, lower-energy cosmic rays passing through dense matter, and nucleosynthesis in violent events in distant galaxies will put nuclear astrophysics on an observational basis. Detection of such lines at a sensitivity of 2 x 10t6 photon cmt2 sect1 (1/10 that of the HEAO-C'instrument)
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From page 69... ...
Many experiments in a developing scientific field, such as low-energy gamma-ray astronomy, require a close and timely interaction between technical developments and scientific discoveries. A system that has basic capabilities for mounting fairly large and massive instruments with modest pointing requirements is needed during the early Shuttle era.
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From page 70... ...
D Cosmic Rays The anticipated large payload capacities of the Shuttle sortie pallets and of Shuttle-launched free-flyers, with correspondingly large detector systems and observation times, promise major scientific advances from detailed studies of the charge, mass, and energy spectra of cosmic rays.
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From page 71... ...
A class of detector systems has been developed that measures both the energy spectra of cosmic rays over the range of 10 to ~ 106 GeV and their elemental abundances from hydrogen through iron, with typical resolution of 50.2 charge unit. These detectors include possible combinations of ionization calorimeters, superconducting magnets, and multithreshold Cerenkov counters.
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From page 72... ...
* 3 £ ^ uj01 •f o-S 3» • - ^ 1 3 •£t "> o c .1 c3« o o " iy Investigate isurement Objec tie Pallet (S)
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From page 73... ...
The study of the isotopic abundances of cosmic rays at low and at high energies is a vital but relatively unexplored new area of cosmicray astrophysics. To date only the low-energy isotopes of hydrogen and helium have been measured.
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From page 74... ...
6. Experiments on Eccentric Orbit and Deep-Space Spacecraft In addition to these requirements of high-energy cosmic-ray astrophysics, the Shuttle has an important function as launch platform for both highly eccentric satellites as well as Tug-assisted deep-space missions, which serve the studies of solar energetic particle phenomena and in situ investigations of low-energy interstellar cosmic rays.
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From page 75... ...
There should be no radiation sources on board, and no large changes of background-producing masses or release of large quantities of material should occur. External magnetic fields should be small (roughly a few gauss)
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From page 76... ...
Large national facilities require a new management/ investigator approach.
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From page 77... ...
The ability of the Shuttle to check out spacecraft in space, recover malfunctioning spacecraft, refurbish standardized spacecraft, and refly instrumentation enables an investigator to carry through from development to spacecraft flight with a single basic instrument. The PI would, under this system, carry out a complete research program over the period of a decade without the major perturbations of specific flight instrumentation construction or the long and expensive
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From page 78... ...
B National Facilities Large national facilities require major commitments in national resources.
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From page 79... ...
The Summer Study group identified approximately 60 high-energy astrophysics groups that are presently pursuing active experimental research programs and that are capable of mounting valuable scientific investigations during the period from 1980 to 1991. The mission model developed here assumes the continuation of the present NASA automated, balloon, and rocket programs as outlined in the NASA mission model through the 1970's.
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From page 80... ...
. It has been assumed that the balloon and sounding-rocket programs will continue into the TABLE 8 High-Energy Astrophysics Mission Model -- Sortie Model 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 Number of pallet elementsa a.
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From page 81... ...
3. We recommend that the HEAO program, which was recently considerably reduced, be continued and expanded, since it will extend naturally into the Shuttle era and forms the basis of our free-flyer concepts; that the developed and ready-for-construction instruments left over from the earlier HEAO program be implemented on either unmanned or Shuttle-launched missions in the late 1970's or very early 1980's.
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From page 82... ...
We recognize that in addition to the large free-flyers there must be a range of opportunities from rockets and balloons to inexpensive single-experiment spacecraft. We regard the Shuttle sortie mode pallet as at least equivalent to a one-week or longer rocket or balloon flight with considerable enhanced capabilities.
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