Engineering topics

Gilman, D. A.

Publications and source records attributed to Gilman, D. A..

4 records

NASA NTRS1986

An upper limit to X-ray emission from Saturn

X-rays are produced in auroral discharges, and their measurement can serve to characterize the interaction processes responsible for the aurora itself. The existence of auroral activity on Saturn was suggested by the observation of a magnetosphere by Pioneer 11 and confirmed by UV measurements during the Voyager encounters. The detection of X-rays from Jupiter with the Einstein Observatory (HEAO 2) satellite provided the impetus for a subsequent observation of Saturn. No emission was detected. This article presents the upper limit established by the observation and derives an expected emission level assuming X-ray production to be the result of bremsstrahlung from keV electrons precipitating into Saturn's atmosphere. The difference is a factor of 100.

Gilman, D. A.↗

NASA NTRS1983

The detection of X rays from Jupiter

X rays in the energy band 0.2-3.0 keV have been detected coming from both polar regions of Jupiter. The observations were made in 1979 and 1981 by using the imaging proportional counter and high resolution imaging detectors on the Einstein X-ray astronomy satellite. The measured flux density of approximately 0.0006/sq cm-sec at earth corresponds to an X ray luminosity of approximately 4 x 10 to the 9th W in the 0.2- to 3.0-keV energy band. The energy spectrum of the X rays is extremely soft and can be characterized by a power law with an exponent of approximately 2.3. Detector energy resolution is insufficient to distinguish a soft line spectrum from a continuum. However, the shape of the response and the observed X ray power indicate that the source of this auroral emission is not electron bremsstrahlung as on the earth, but is most probably line emission from O and S ions with energies between 0.03 and 4.0 MeV/nucleon precipitating from the outer boundary of the Io plasma torus at L approximately 8.

Metzger, A. E.↗

NASA NTRS1978

The galactic gamma-ray flux in the 0.06 to 5 MeV range

Gamma ray emission from the longitude range -50 deg less than or equal to lambda less than or equal to 22 deg recorded by the Apollo gamma-ray spectrometer and by individual observers is discussed. Agreement of the galactic emission spectra near 1 MeV with hard X-ray observations of the galactic central regions suggests that an ensemble of point sources is responsible for the emissions. Apollo 16 upper limits to the cosmic 4.4 MeV line flux imply that the ratio of line strength to continuum emission for the region observed by Haymes et al is higher than the galactic average.

Gilman, D. A.↗

NASA NTRS1974

A cosmic gamma ray burst measured by Apollo 16

A cosmic gamma ray burst at about 1058:21 UT on April 27, 1972, was detected with an omnidirectional scintillation counter on Apollo 16. The event whose energy was approximately 0.0002 erg/sq cm, was pulse height analyzed in 512 channels over the 0.067 less than or equal to E less than or equal to 5 MeV range, and shows a complex, multipeak structure on a 300 msec time scale. The burst was also measured by a collimated X-ray detector on Apollo 16, giving spectral data in the 2 to 8 keV range which, together with a simultaneous observation by Vela 6A, allows a directional determination.

Matteson, J. L.↗