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At least 199 records · Page 11
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NASA NTRS1975

X-ray and gamma-ray astronomy

Accomplishments in the fields of X-ray and gamma ray astronomy are discussed. Data obtained from IMP and OGO satellites are analyzed to determine the sources of interplanetary radiation bursts. The energy spectrum of cosmic gamma ray bursts as observed by IMP-6 is described. The application of cooling blackbody techniques as a method for examining cosmic gamma ray bursts is reported. The experimental results and theoretical interpretation of high energy diffuse gamma rays are investigated. The structure of the SAS-2 satellite is depicted and the accomplishments are examined. Other sources of gamma radiation to include galactic fermi, Cygnus X-1, supernovae, and the planet Jupiter are proposed. Data obtained from the Pioneer 10 space probe are presented in graph form.

Source record↗
NASA NTRS1974

The distribution of cosmic rays in the galaxy and their dynamics as deduced from recent gamma ray observations

Data from SAS-2 on the galactic gamma ray line flux as a function of longitude is examined. It is shown that the gamma ray emissivity varies with galactocentric distance and is about an order of magnitude higher than the local value in a toroidal region between 4 and 5 kpc from the galactic center. This enhancement is accounted for in part by first-order Fermi acceleration, compression, and trapping of cosmic rays consistent with present ideas of galactic dynamics and galactic structure theory. Calculations indicate that cosmic rays in the 4 to 5 kpc region are trapped and accelerated over a mean time of the order of a few million years or about 2 to 4 times the assumed trapping time in the solar region of the galaxy on the assumption that only an increased cosmic ray flux is responsible for the observed emission. Cosmic ray nucleons, cosmic ray electrons, and ionized hydrogen gas were found to have a strikingly similar distribution in the galaxy according to both the observational data and the theoretical model discussed.

Puget, J. L.↗
NASA NTRS1974

Radio and gamma ray evidence for a molecular-arm feature at 5 kpc from the galactic centre

Recent measurements of the galactic CO distribution as evidenced from 2.6 mm radio observations of the CO emission line intensity are correlated with the SAS-2 measurements of galactic gamma ray emission. Both distributions are indicative of a ring-shaped distribution or arm consisting of cool clouds of molecular hydrogen at a galactocentric distance of approximately 5 kpc. The mean density of H2 in this region is estimated to be between 1 and 5 cu cm. Both a galactic and extra-galactic origin of cosmic rays are consistent with the observations, although the presence of dynamical effects and increased star formation at 5 kpc in the dense molecular clouds may be connected with an increase in cosmic-ray production.

Solomon, P. M.↗
NASA NTRS1975

Selected Theoretical Studies Group contributions to the 14th International Cosmic Ray conference

The galactic distribution of H2 was studied through gamma radiation and through X-ray, optical, and infrared absorption measurements from SAS-2 and other sources. A comparison of the latitude distribution of gamma-ray intensity with reddening data shows reddening data to give the best estimate of interstellar gas in the solar vicinity. The distribution of galactic cosmic ray nucleons was determined and appears to be identical to the supernova remnant distribution. Interactions between ultrahigh energy cosmic-ray nuclei and intergalactic photon radiation fields were calculated, using the Monte Carlo method.

Source record↗
NASA NTRS1974

Burst-error characteristics of the equatorial transionospheric channel

Analyses of AGC analog data from the Small Astronomy Satellite (SAS) at VHF (136 MHz) have shown amplitude fluctuations in the signals received at several equatorial tracking sites operated by NASA. Errors in data are shown to increase markedly for nighttime satellite passes around the periods of the two equinoxes as compared to the errors observed during other periods. Qualitative and quantitative correlations are established between the ionospheric scintillation phenomenon and the occurrence of errors. Strong time and geographic cause-and-effect relationships are established by determining the statistical correlation between scintillation indices and bit error rates. Detailed analyses of the AGC fading statistics and the fine grain error statistics, such as the block-error distribution and the bit-error autocorrelation function, establish the strong correlation between deep fades and their effects on the burst error structure associated with the transionospheric channel and the communication receiver being employed.

Blank, H. A.↗
NASA NTRS1975

Upper limits of hard gamma-ray emission from six X-ray sources

The Cornell 100-inch gamma-ray telescope has been used to set upper limits for the gamma-ray flux above 400 MeV from the X-ray sources Cyg X-1, Cyg X-2, Cyg X-3, Cas A, Cas B, and Per X-1. An upper limit for the diffuse flux of the galactic disk was set which is consistent with OSO-3 and SAS-2 data. A new measurement of the atmospheric gamma-ray generation rate is presented.

Campbell, M.↗
NASA NTRS1975

High-energy gamma-ray results from the second small astronomy satellite

Data are reported which were obtained with a high-energy (exceeding 35 Mev) gamma-ray telescope flown on the second Small Astronomy Satellite (SAS-2). The high-energy galactic gamma radiation is observed to dominate over the general diffuse radiation along the entire galactic plane, and its longitudinal and latitudinal distributions appear to be generally correlated with galactic structural features, particularly with arm segments. Principally on the basis of its angular distribution and magnitude, it is suggested that this radiation results primarily from cosmic-ray interactions with interstellar matter. A uniform celestial gamma radiation appears to have been detected; the form of its differential spectrum over the energy range from about 35 to 170 MeV is obtained, and a cosmological origin is suggested for this radiation. In addition to the general galactic emission, high-energy gamma radiation was detected from the Crab Nebula, Vela X, a general region toward the galactic center, and a region located a few degrees north of the galactic plane. Upper limits to the high-energy gamma ray fluxes are set for a number of localized sources.

Fichtel, C. E.↗
NASA NTRS1976

Gamma-rays, cosmic rays, and galactic structure

The relation of SAS-2 observations of galactic gamma-rays to the large scale distribution of cosmic rays and interstellar gas in the galaxy is reviewed. Starting with a discussion of production rates, the case for pion decay being the predominant production mechanism in the galactic disk above 100 MeV is reestablished, and it is also pointed out that Compton gamma-rays can be a significant source near l = 0. The concepts of four distinct galactic regions are defined, viz. the nebulodisk, ectodisk, radiodisk and exodisk. Bremsstrahlung and pion decay gamma-rays are associated with the first two (primarily the first) regions, and Compton gamma-rays and synchrotron radiation are associated with the latter two regions. On a large scale, the cosmic rays, interstellar gas (primarily H2 clouds in the inner galaxy) and gamma-ray emissivity all peak between 5 and 6 kpc from the galactic center. This correlation is related to correlation with other population I phenomena and is discussed in terms of the density wave concept of galactic structure.

Stecker, F. W.↗
NASA NTRS1976

The structure and content of the galaxy and galactic gamma rays

Papers are presented dealing with galactic structure drawing on all branches of galactic astronomy with emphasis on the implications of the new gamma ray observations. Topics discussed include: (1) results from the COS-B gamma ray satellite; (2) results from SAS-2 on gamma ray pulsar, Cygnus X-3, and maps of the galactic diffuse flux; (3) recent data from CO surveys of the galaxy; (4) high resolution radio surveys of external galaxies; (5) results on the galactic distribution of pulsars; and (6) theoretical work on galactic gamma ray emission.

Fichtel, C. E.↗
NASA NTRS1976

COS-B observations of localised sources of gamma-ray emission

In October 1975 the high energy gamma ray flux from the Vela pulsar was measured by COS-B to be 1.6 to 2.1 times higher than the flux measured by SAS-2 in 1973. The existence is confirmed of a second region of enhanced radiation in the galactic anticenter in addition to that from the Crab pulsar.

Mayer-Hasselwander, H.↗
NASA NTRS1976

Gamma rays, cosmic rays and galactic structure

Working primarily from the recent SAS-2 observations of galactic gamma rays, the relation of these observations to the large scale distribution of cosmic rays and interstellar gas in the galaxy is reviewed and reexamined. Starting with a discussion of production rates, the case for pion decay being the predominant production mechanism in the galactic disk above 100 MeV is reestablished and it is also pointed out that Compton gamma rays can be a significant source. To facilitate discussion, the concepts of four distinct galactic regions are defined, viz. the nebulodisk, ectodisk, radiodisk and exodisk. Bremsstrahlung and pion decay gamma rays are associated with the first two (primarily the first) regions, and Compton gamma rays and synchrotron radiation are associated with the latter two regions. On a large scale, the cosmic rays, interstellar gas (primarily H2 clouds in the inner galaxy) and gamma ray emissivity all peak in a region between 5 and 6 kpc from the galactic center. This correlation is related to correlation with other population I phenomena and is discussed in terms of the density wave concept of galactic structure. The singular nature of the HI distribution appears to follow the supernova remnant and pulsar distributions in the galaxy.

Stecker, F. W.↗
NASA NTRS1976

Design of a control configured tanker aircraft

The benefits that accrue from using control configured vehicle (CCV) concepts were examined along with the techniques for applying these concepts to an advanced tanker aircraft design. Reduced static stability (RSS) and flutter mode control (FMC) were the two primary CCV concepts used in the design. The CCV tanker was designed to the same mission requirements specified for a conventional tanker design. A seven degree of freedom mathematical model of the flexible aircraft was derived and used to synthesize a lateral stability augmentation system (SAS), a longitudinal control augmentation system (CAS), and a FMC system. Fatigue life and cost analyses followed the control system synthesis, after which a comparative evaluation of the CCV and conventional tankers was made. This comparison indicated that the CCV weight and cost were lower but that, for this design iteration, the CCV fatigue life was shorter. Also, the CCV crew station acceleration was lower, but the acceleration at the boom operator station was higher relative to the corresponding conventional tanker. Comparison of the design processes used in the CCV and conventional design studies revealed that they were basically the same.

Walker, S. A.↗
NASA NTRS1976

B-52 stability augmentation system reliability

The B-52 SAS (Stability Augmentation System) was developed and retrofitted to nearly 300 aircraft. It actively controls B-52 structural bending, provides improved yaw and pitch damping through sensors and electronic control channels, and puts complete reliance on hydraulic control power for rudder and elevators. The system has experienced over 300,000 flight hours and has exhibited service reliability comparable to the results of the reliability test program. Development experience points out numerous lessons with potential application in the mechanization and development of advanced technology control systems of high reliability.

Bowling, T. C.↗
NASA NTRS1976

Observation of gamma rays with a 4.8 hour periodicity from CYG X-3

Energetic (E35 MeV) Gamma rays were observed from Cyg X-3 with the SAS-2 Gamma ray telescope. They are modulated at the 4.8 sup h period observed in the X-ray and infrared regions, and within the statistical error are in phase with this emission. The flux above 100 MeV has an average value of (4.4 + or - 1.1)x 10 to the -6 power/sq cm/sec. If the distance to Cyg X-3 is 10 kpcs, this flux implies a luminosity of more than 10 to the 37th power ergs/s if the radiation is isotropic and about 10 to the 36th power ergs/s if the radiation is restricted to a cone of one steradian, as it might be in a pulsar.

Lamb, R. C.↗
NASA NTRS1975

Recent observations of cosmic gamma-ray bursts

The paper summarizes current knowledge of cosmic gamma ray bursts obtained from recent spaceborne observations. Three facts lie at the basis of interpreting gamma ray burst observations: (1) all measured event differential energy spectra appear to be alike, (2) there is no evidence that the event integral size spectrum departs from a -1.5 power law, and (3) the temporal structures of most events are consistent with a continuous flutter down to at least 30 msec throughout the event histories. Event-average spectra of 9 bursts observed with IMP-7 are presented, and the Vela size spectrum is compared with IMP-7 points, SAS-2 events, and balloon experiment limits.

Cline, T. L.↗
NASA NTRS1976

The transient periodic X-ray source in Taurus, A0535+26

Eighteen X-ray light curves of the 104-sec periodicity in the Taurus X-ray nova A 0535+26 are analyzed which were obtained by SAS-3 in six energy intervals between 1 and 35 keV during the period from May 30 to June 2, 1975. It is shown that the pulse structure is relatively simple at energies above 19 keV, but develops a complex series of five irregularly spaced maxima at lower energies. The energy spectrum averaged over the 104-sec period is found to be extremely hard, with a best-fit temperature of about 30 keV for the exponential spectrum, an excess at about 15 keV, and a steepening above 20 keV. It is suggested that A 0535+26 may be a compact object in a binary system containing the peculiar Be star HDE 245770. The transient behavior could arise due to episodic mass loss by the primary or because the compact object is in a highly eccentric orbit about the companion, with appreciable mass transfer occurring only at periastron.

Bradt, H.↗
NASA NTRS1975

Galactic gamma radiation from cosmic rays concentrated in spiral arms

Extending the model proposed by Bignami et al. (1975), and by Fichtel et al. (1975a) for the production of the galactic high energy gamma ray distribution observed by SAS-2 to lower energies indicates the radiation is dominated by the bremsstrahlung emission of cosmic ray electrons traversing the interstellar gas. Although secondary electrons contribute only about 15% to the 10-30 MeV gamma ray emission in the solar vicinity, their contribution in the model is proportional to the third power of N, where N(r, gal. long., gal. lat.) is the total interstellar gas density, as compared to the square of N for the case of the primary components, and hence their relative importance increases in high density regions. Gamma-ray observations at these energies when compared to those at high energies (above 100 MeV) may provide a means for mapping the ratio of cosmic ray electrons to nucleons throughout the galaxy without the necessity of invoking models for the galactic magnetic field.

Kniffen, D. A.↗
NASA NTRS1975

Interstellar reddening and gamma-ray emission as tracers of interstellar matter

It is shown that the gas to dust ratio in our galaxy is almost constant, even in regions of very different densities. The detailed comparison of the latitude distribution of the gamma-ray intensity with reddening data shows that in the solar vicinity the latter gives the best estimate of the total amount of interstellar gas. This conclusion is used to compute the nearby contributions to the gamma-rays longitude distribution observed by SAS II. Some implications for the large scale structure of the galaxy are examined.

Puget, J. L.↗