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Fichtel, C. E.

Publications and source records attributed to Fichtel, C. E..

At least 127 records · Page 7
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NASA NTRS1975

Observations of low energy gamma-ray bursts with SAS-2

The present paper reports on the low-energy gamma-ray bursts observed by the plastic scintillator anticoincidence dome of the Small Astronomy Satellite-2 (SAS-2) gamma-ray telescope. SAS-2 detected two events observed by other satellites and discovered one which was subsequently confirmed by other satellite observations. Two events seen by other satellites were not detected by SAS-2, probably due to earth occultation. The event detection threshold for SAS-2 was almost two orders of magnitude lower than that of the Vela satellites.

Oegelman, H.↗
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 NTRS1975

SAS-2 High energy gamma-ray observations of the Vela pulsar

The second Small Astronomy Satellite high-energy (35 MeV) gamma-ray telescope detected pulsed gamma-ray emission at the radio period from PSR 0833-45, the Vela pulsar, as well as an unpulsed flux from the Vela region. The pulsed emission consists of two peaks, one following the radio peak by about 13 msec, and the other 0.4 period after the first. The luminosity of the pulsed emission above 100 MeV from Vela is about 0.1 that of the pulsar NP0532 in the Crab nebula, whereas the pulsed emission from Vela at optical wavelengths is less than 0.0004 that from the Crab. The relatively high intensity of the pulsed gamma-ray emission and the double peak structure, compared to the single pulse in the radio emission, suggests that the high energy gamma-ray pulsar emission may be produced under different conditions from those found at lower energies.

Thompson, D. J.↗
NASA NTRS1975

Primary gamma-rays

Within our Galaxy, cosmic rays can reveal their presence in interstellar space and probably in source regions by their interactions with interstellar matter which lead to gamma-rays with a very characteristic energy spectrum. From the study of the intensity of the high energy gamma radiation as a function of galactic longitude, it is already clear that cosmic rays are almost certainly not uniformly distributed in the Galaxy and are not concentrated in the center of the Galaxy. The galactic cosmic rays appear to be tied to galactic structural features, presumably by the galactic magnetic fields which are in turn held by the matter in the arm segments and the clouds. On the extra-galactic scale, it is now possible to say that cosmic rays are probably not at the density seen near the earth.

Fichtel, C. E.↗
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

Distribution of cosmic gamma rays in the galactic anticenter region as observed by SAS-2

The high energy (above 35 MeV) gamma ray telescope flown on the second Small Astronomy Satellite has collected over one thousand gamma rays from the direction of the galactic anticenter. In addition to the diffuse galactic emission the distribution indicates a strong pulsed contribution from the Crab nebula with the same period and phase as the NP0532 pulsar. There also seems to be an excess in the direction of (gal. long. ? 195 deg; gal. lat ? +5 deg) where there is a region containing old supernova remnants. Search for gamma ray pulsations from other pulsars in the region do not show any statistically significant signal. The general intensity distribution of the gamma rays away from the plane appear to be similar to nonthermal radio emission brightness contours.

Kniffen, D. A.↗
NASA NTRS1975

Gamma ray astronomy

A review is given of recent papers in the field of gamma-ray astronomy. It is mentioned that the strongest feature of the gamma ray sky is the general radiation from the galactic plane which is superimposed on what appears to be a general diffuse radiation, whose properties are not yet defined. The observation of high-energy galactic gamma radiation by the SAS-2 satellite is considered as is the observation of point and localized sources (the Crab Nebula, Vela, etc.). The observation of diffusive gamma radiation is discussed.

Fichtel, C. E.↗
NASA NTRS1974

High energy galactic gamma radiation from cosmic rays concentrated in spiral arms

A model for the emission of high energy ( 100 MeV) gamma rays from the galactic disk was developed and compared to recent SAS-2 observations. In the calculation, it is assumed that (1) the high energy galactic gamma rays result primarily from the interaction of cosmic rays with galactic matter; (2) on the basis of theoretical and experimental arguments the cosmic ray density is proportional to the matter density on the scale of galactic arms; and (3) the matter in the galaxy, atomic and molecular, is distributed in a spiral pattern consistent with density wave theory and the experimental data on the matter distribution.

Bignami, G. F.↗
NASA NTRS1974

SAS-2 observations of celestial diffuse gamma radiation above 30 MeV

The small astronomy satellite, SAS-2, used a 32-deck magnetic core digitized spark chamber to study gamma rays with energies above 30 MeV. Data for four regions of the sky away from the galactic plane were analyzed. These regions show a finite, diffuse flux of gamma rays with a steep energy spectrum, and the flux is uniform over all the regions. Represented by a power law, the differential energy spectrum shows an index of 2.5 + or - 0.4. The steep SAS-2 spectrum and the lower energy data are reasonably consistent with a neutral pion gamma-ray spectrum which was red-shifted (such as that proposed by some cosmological theories). It is concluded that the diffuse celestial gamma ray spectrum observed presents the possibility of cosmological studies and possible evidence for a residual cosmic ray density, and supports the galactic superclusters of matter and antimatter remaining from baryon-symmetric big bang.

Thompson, D. J.↗
NASA NTRS1974

SAS-2 observations of gamma rays from the galactic plane

Preliminary data are given for the SAS-2 high energy galactic gamma ray observation. These data include both latitude and longitude distributions. The longitude distribution shows a high density region. The latitude distributions toward the center and the anti-center are markedly different, the former showing a two-component structure of half-widths of approximately 3 and 6 deg. The energy spectrum in the range 35 to 200 MeV is hard, consistent with cosmic ray interactions with interstellar matter, including neutral pions decay and emission from energetic electron interactions. The data is consistent with an interpretation in terms of the confinement of the cosmic rays in the spiral arms.

Thompson, D. J.↗
NASA NTRS1974

Observations of discrete gamma ray sources with SAS-2

Compact gamma ray sources centered on the Crab nebula and the Vela X supernova remnant are considered. An excess in the galactic radiation was observed in both regions. Data indicate that a large fraction of this flux is pulsed. The excess from the Vela region could reflect either a large-scale galactic feature, such as a superposition of spiral arm segments, or it could be associated with the Vela supernova remnant. Low-energy gamma ray bursts were observed in the SAS-2 anticoincidence shielding.

Thompson, D. J.↗
NASA NTRS1974

High energy gamma ray results from the second small astronomy satellite

A high energy (35 MeV) gamma ray telescope employing a thirty-two level magnetic core spark chamber system was flown on SAS 2. The high energy galactic gamma radiation is observed to dominate over the general diffuse radiation along the entire galactic plane, and when examined in detail, the longitudinal and latitudinal distribution seem generally correlated with galactic structural features, particularly with arm segments. The general high energy gamma radiation from the galactic plane, explained on the basis of its angular distribution and magnitude, probably results primarily from cosmic ray interactions with interstellar matter.

Fichtel, C. E.↗
NASA NTRS1974

Gamma radiation from the Crab nebula above 35 MeV

Electromagnetic radiation from the Crab nebula were observed, showing that the Crab is unique among strong X-ray sources in that major component in the low energy range (1 to 10 KeV) shows little or no temporal variation. Observations of the Crab above 35 MeV were made with the high energy gamma ray telescope flown on SAS-2. The detector and technique are described in detail.

Kniffen, D. A.↗
NASA NTRS1974

High energy gamma ray astronomy

The SAS-2 gamma ray experiment and its detection of celestial gamma rays are described. Data also cover intensity of high energy gamma rays, gamma ray distribution, gamma ray origin, and diffuse radiation.

Fichtel, C. E.↗
NASA NTRS1974

Galactic arm structure and gamma-ray astronomy

In an attempt to explain the observed unexpectedly high-energy gamma-radiation over a broad region of the galactic plane in the general direction of the galactic center, a model is proposed wherein the galactic cosmic rays are preferentially located in the high-matter-density regions of galactic arm segments, as a result of the weight of the matter in these arms tying the magnetic fields and hence the cosmic rays to these regions. The presently observed longitudinal distribution of galactic gamma-rays can be explained with the current estimate of the average galactic matter density, if the average ratio of arm to interarm matter is 5:1 for the major arm segments toward the galactic center from the sun, and if the cosmic-ray density normalized to its local value is assumed to be directly proportional to the matter density.

Bignami, G. F.↗