Engineering topics

Norris, J. P.

Publications and source records attributed to Norris, J. P..

41 records · Page 3

NASA NTRS1986

Spectral evolution in gamma-ray bursts

The Hard X-ray Burst Spectrometer (HXRBS) and the Gamma-Ray Spectrometer (GRS) on NASA's Solar Maximum Mission satellite have independently monitored cosmic gamma-ray bursts since launch in February 1980. Several bursts with relatively simple pulse structure and sufficient intensity have been analyzed for evidence of spectral variability on time scales shorter than the pulse durations. In many of these bursts pulse structures are found, ranging in duration from 1 to 10 seconds, which exhibit a trend of hard-to-soft spectral evolution. No significant evidence for soft-to-hard evolution has been found. The HXRBS data above 100 keV and the GRS data above 1 MeV indicate that the spectral evolution generally is not due to time-varying absorption features at energies below 100 keV.

Norris, J. P.↗

NASA NTRS1984

Frequency of fast, narrow gamma-ray bursts

A duration histogram for 24 gamma-ray burst events detected by an ISEE-3 experiment is presented which suggests the existence of two gamma-ray burst populations. A distribution is also shown of 123 Venera 13 and 14 events which suggests two such populations in each experimental sample, the domains separated with a minimum near 1 or 2 sec. It is pointed out that the results of the Goddard ISEE-3 gamma-ray burst spectrometer actually enhance the appearance of two burst populations suggested in the Venera data.

Norris, J. P.↗

NASA NTRS1983

Frequency of Fast, Narrow Gamma-ray Bursts and Burst Classification

Evidence from the Vela satellites that very brief, approximately 0.1 s, gamma-ray bursts constitute a class distinct from the longer, highly structured bursts has been strengthened by the results of the Venera 11 and 12 KKONUS experiments. The Goodard ISEE-3 gamma-ray burst spectrometer, utilizing a trigger criterion which is more likely to be independent of duration than previous experiments, detected a sample of events which enhances this bimodal distribution. The ISEE-3 result is corroborated by an increase in the frequency of detection of short bursts in the KONUS 13/14 database over KONUS 11/12, an effect attributable to the use of a shorter trigger integration time in the later experiments. Considerations such as repeating bursters complicate a simple dichotomous classification of gamma-ray bursts.

Norris, J. P.↗

NASA NTRS1983

Gamma-ray burst high time-resolution spectral observations made with the Solar Maximum Mission

The gamma-ray bursts of April 19 and 21, 1980, and March 1, 1981, are characterized on the basis of observations obtained at 25-500 keV and time resolution 128 msec using the hard-X-ray-burst spectrometer of the SMM satellite. The data are presented graphically, and the parameters determined by fitting three theoretical models to the data for each phase (rising phase, decay phase, and valleys between pulses) are given in tables. Models used are thin thermal bremsstrahlung with or without absorption lines, thermal synchrotron with or without absorption lines, and power law with exponential cutoff.

Desai, U. D.↗

NASA NTRS1982

Search for time variations in 511 keV flux by ISEE-3 gamma-ray spectrometer

Upper limits to the variation of galactic 511 keV flux as observed by the ISEE-3 gamma-ray spectrometer for 500 days of nearly continuous observation are reported. It is pointed out that if sources similar to the galactic center source were distributed uniformly throughout the Galaxy, a source within 2-3 kpc could have been detected by the ISEE-3 spectrometer. The lack of detection is evidence that the galactic center source is unique within the Galaxy. The galactic center observations made with the HEAO-3 gamma-ray spectrometer are seen as supporting the contention that a time-varying source is 511 keV emission lies near the galactic center.

Norris, J. P.↗