Engineering topics

White, R. S.

Publications and source records attributed to White, R. S..

At least 19 records

NASA NTRS1997

Few arc-minute and keV resolutions with the TIGRE Compton telescope

The tracking and imaging gamma ray experiment (TIGRE) Compton telescope concept can provide an angular resolution of a few arcmin, an energy resolution of a few keV and high sensitivity, while providing the wide field of view necessary for surveying and monitoring observations. Silicon and CdZnTe strip detectors are used to detect Compton pair events and determine their incident directions and energies. Above 400 keV, Compton recoil electrons are tracked through successive layers of thin silicon strip detectors. Compton scattered photons are detected with CdZnTe strip detectors. Pair electrons and positrons are tracked to provide high sensitivity observations in the 10 to 100 MeV range. Polarization studies are performed with large angle Compton scatter events. The TIGRE concept and development status are described.

Zych, A.↗

NASA NTRS1992

The spatial distribution of gamma-ray bursts from Pioneer Venus Orbiter

The homogeneity of the burst source population in space with the log N(greater than P sub c)-log P sub c and log (dN/dP sub c)-log P sub c relations is studied on the basis of a sample of 225 observed gamma-ray bursts between September 1978 and July 1988 from the Pioneer Venus Orbiter. The relations N(greater than P sub c) is approximately equal to P sub c exp -1.5 and dN/dP sub c is approximately equal to P sub c exp -2.5 are expected if the gamma bursters are uniformly distributed in space. The Kolmogorov-Smirnov statistic gives a probability of 0.93 that the observed integral distribution N(greater than P sub c) is drawn from the expected uniform distribution P sub c exp -1.5. A least-squares 1 standard deviation fit to the observed differential distribution yields dN/dP sub c of about P sub c -2.42 +/- 0.07. Both are consistent with a uniform distribution in space of the parent population of burst sources.

Chuang, K. W.↗

NASA NTRS1992

Compton telescope observations of gamma rays from SN 1987A

Results are reported of observations of a significant excess of gamma rays at energies of 1.0-2.5 MeV from the direction of SN 1987A, 418 days after detonation. Two features at 1.21 and 1.88 MeV are attributed to the 1.238 MeV and the combined 1.771, 2.015, and 2.035 MeV line emissions from the decay of Co-56 in the expanding ejecta with respective fluxes of (4.6 +/-1.4 +/-1.2) x 10 exp -4 and (3.5 +/-0.9 +/-0.9) x 10 exp -4 gamma/sq cm s, where the first error is statistical and the second systematic. The obtained energy resolution of 11 percent did not permit a definite separation of the 1.771-MeV line from the two other lines at 2.015 and 2.035 MeV that form the group at 1.88 MeV. The line fluxes were obtained after correcting for the north-south effect and the continuum.

Ait-Ouamer, Farid↗

NASA NTRS1992

Method of separation of celestial gamma-ray bursts from solar flares

We recently discovered 217 'new' celestial gamma-ray burst candidates from the 'new' burst search of the PVO real time data base. The burst search covered the time period from September 1978 to July 1988. Sixty were confirmed by at least one other spacecraft, e.g., ISEE-3, V-II, V-12, etc. None triggered the PVO high time resolution memory. In this paper we describe a new algorithm based on the relationship between time width T(w) and hardness ratio HR, to distinguish cosmic gamma-ray bursts from solar flares without knowing the directions of the events. The algorithm was tested with 83 triggered and 60 nontriggered confirmed gamma-ray bursts and 30 confirmed solar flares from PVO.

Chuang, K. W.↗

NASA NTRS1991

On the influence of the magnetization of a modal solar wind on a laboratory magnetosphere

The interaction of a magnetized plasma beam with a stationary dipole field, analogous to the interaction of the solar wind with the earth's magnetosphere, is explored in a laboratory experiment. Experimental parameters are chosen to scale qualitatively similar to the parameters in the earth's magnetosphere. It is found that the magnetization of the laboratory 'solar wind', generated by injecting a plasma across a preexisting magnetic field, requires a certain minimum magnetic field strength. Differences between the resulting magnetospheres for northward and southward 'solar wind' or 'interplanetary' magnetic fields (IMF) are demonstrated by global pictures and by magnetic field measurements above the north polar region. These measurements show patterns of the variation of the transverse field component which are similar to those found by satellite measurements above the earth. This indicates the presence of similar field-aligned current systems. Particularly, the presence (for northward IMF) and absence (for southward IMF) of the pattern attributed to the 'NBZ' (northward Bz) current system are demonstrated.

Rahman, H. U.↗

NASA NTRS1989

Laboratory simulation of cometary neutral gas ionization

The laboratory simulation of the interaction of the solar wind with a comet is used to study the cometary neural gas ionization. The experiment is carried out in the UCR T-1 facility with an ice ball as the comet model. Photographs and data are taken with a variety of values of the solar wind velocity, interplanetary magnetic field (IMF), and comet configurations. The results show that the cometary neutral gas ionization depends on both the velocity of the solar wind and the interplanetary magnetic field. The plasma cloud surrounding the comet is visible only when the solar wind velocity and IMF are both above certain minimum values. This velocity dependent phenomena is explained by Alfven's critical ionization velocity effect. The critical magnetic field may be explained by assuming two stream lower hybrid instability as a triggering mechanism for the ionization of the neutral gas by plasma flow. Critical upper and lower limits for the magnetic field, required by anomalous ionization, are also derived that satisfy the experimental observations.

Chang, Tsuey-Fen↗

NASA NTRS1988

The gamma ray north-south effect

Theoretical calculations are presented that explain the balloon observations by O'Neill et al. (1987) of a strong north-south anisotropy of atmospheric gamma rays over the Southern Hemisphere, and to predict the north-south ratios. It is shown that the gamma rays that originate at the longest distances from the telescopes give the largest north-south ratios. Comparisons are made of the experimental north-south ratios measured on balloons launched from Alice Springs, Australia, and from Palestine, Texas, U.S., and predictions are made for ratios at other geomagnetic latitudes and longitudes. It is pointed out that observers who measure backgrounds for celestial sources may be misled unless they correct for the north-south effect.

White, R. S.↗

NASA NTRS1988

The UCR gamma ray telescope data acquisition system

A description is given of an electronics system based on the DEC Falcon SBC-11/23+, which has been designed and built to support a balloon-borne double Compton gamma-ray telescope. The system provides support for commands, data acquisition, data routing and compression, and photomultiplier tube gain control. The software consists of a number of interrupt-driven routines of differing priorities to handle each system task. This includes two circular buffers for onboard processing and bit encoding before transmission of the information to the ground computer. Acquisition of gamma-ray events at rates above the 200-Hz telemetry constraint is easily achieved.

O'Neill, T. J.↗

NASA NTRS1986

An acceleration mechanism for cometary plasma tails

Cometary plasma tail formation by the interaction between the solar wind plasma flow and the plasma at the head of the coma is discussed using the unipolar electric generation theory. The plasma in the 'plasma tail' is almost directly accelerated from the cometary ionopause along the sun-nucleus line where the tail current flows. For steady state solar wind conditions, the cometary 'plasma tail' velocity distribution is obtained self-consistently. The solution of a kinetic equation gives the velocity of the cometary plasma as a function of the cometary tail position. The characteristic length is 3 x 10 to the 6th km when the plasma density near the nucleus of the comet is 10 to the 6th/cu cm and the component of the interplanetary magnetic field perpendicular to the solar wind flow is 3 nT. The tailward cometary plasma is finally accelerated to the speed of the solar wind. The theory is compared with the observational plasma velocities in the tails of comet Bennett (1970II) and Comet Halley (1985).

Minami, S.↗

NASA NTRS1986

Laboratory formation of a simulated comet

A laboratory simulation experiment to study the interaction between a cometary plasma and the solar wind has been performed using the UCR-T1 space simulation facility (dia. 1.3 m, length 11 m). Intense plasma flow simulating the solar wind interacts with another light-emitting plasma composed of Ba, Sr, and/or C by a plasma emitter which simulates a cometary coma. The purposes of this experiment are to investigate how the solar wind parameters contribute to the formation of the cometary ion tail and to determine the magnetic field structure of a comet. In order to estimate the solar wind parameters by ground-based observations of actual comets, knowledges of such relationships are essential. The experimental results show that the interplanetary magnetic field of the solar wind is very important in forming the cometary tail.

Minami, S.↗

NASA NTRS1985

Low-energy and medium-energy gamma rays from PSR 0531 + 21

Results are presented from the Crab Pulsar PSR 0531 + 21 for energies of 0.3-30 MeV. For energies of 1-30 MeV, the absolute phase and separation of the first and second pulses 12.9 + or - 0.3 ms, widths of the pulses 2.2 + or - 0.5 ms FWHM, and 1.6 + or - 0.4 ms FWHM, ratio of the counts in the second to the first pulse 0.64 + or - 0.33 and ratio of counts in the interpulse region to the total pulsed counts 0.17 + or - 0.30 are compared to te results vor energies, E greater than 50 MeV and their variations with time. Values from the phase plots for E greater than 0.3 MeV are compared with low-energy gamma rays during 1970 through 1980 from several experiments with energies from about 20 to 360 keV. The above suggest different production mechanisms for low- and high-energy gamma rays with a transition at about 1 MeV. Derived fluxes from 0.3 to 30 MeV confirm a previously derived power law.

White, R. S.↗

NASA NTRS1985

Gamma rays of 0.3 to 30 MeV from PSR 0531+21

Pulsed gamma rays from the Crab Pulsar PSR 0531+21 are reported for energies of 0.3 to 30 MeV. The observations were carried out with the UCR gamma ray double Compton scatter telescope launched on a balloon from Palestine, Texas at 4.5 GV, at 2200 LT, September 29, 1978. Two 8 hr observations of the pulsar were made, the first starting at 0700 UT (0200 LT) September 30 just after reaching float altitude of 4.5 g/sq cm. Analysis of the total gamma ray flux from the Crab Nebula plus pulsar using telescope vertical cell pairs was published previously. The results presented supersede the preliminary ones. The double scatter mode of the UCR telescope measures the energy of each incident gamma ray from 1 to 30 MeV and its incident angle to a ring on the sky. The time of arrival is measured to 0.05 ms. The direction of the source is obtained from overlapping rings on the sky. The count rate of the first scatter above a threshold of 0.3 MeV is recorded every 5.12 ms. The Crab Pulsar parameters were determined from six topocentric arrival times of optical pulses.

White, R. S.↗

NASA NTRS1985

Measured performance of the new University of California gamma ray telescope

The design of the new medium energy balloon-borne gamma ray telescope is discussed. This telescope is sensitive to 1-30 MeV gamma rays. The results of the initial calibration are described. The position and energy resolutions of 32 plastic and NaI(Tl) scintillator bars, each 100 cm long are discussed. The telescope's measured angular and energy resolutions as a function of incident angle are compared with detailed Monte Carlo calculations at 1.37, 2.75 and 6.13 MeV. The expected resolutions are 5 deg FHWM and 8% at 2.75 MeV. The expected area-efficiency is 250 cm.

Zych, A. D.↗

NASA NTRS1985

Neutron-induced 2.2 MeV background in gamma ray telescopes

Neutron-induced gamma ray production is an important source of background in Compton scatter gamma ray telescopes where organic scintillator material is used. Most important is deuteron formation when atmospheric albedo and locally produced neutrons are thermalized and subsequently absorbed in the hydrogenous material. The resulting 2.2 MeV gamma ray line radiation essentially represents a continuous isotropic source within the scintillator itself. Interestingly, using a scintillator material with a high hydrogen-to-carbon ratio to minimize the scintillator material with a high hydrogen-to-carbon ratio to minimize the neutron-induced 4.4 MeV carbon line favors the np reaction. The full problem of neutron-induced background in Compton scatter telescopes has been previously discussed. Results are presented of observations with the University of California balloon-borne Compton scatter telescope where the 2.2 MeV induced line emission is prominently seen.

Zanrosso, E. M.↗

NASA NTRS1984

Gamma rays of 0.3-30 MeV from PSR0833 - 45

Pulsed gamma rays from the Vela pulsar PSR0833 - 45 are reported for the first time over the medium energy range 0.3-30 MeV. They were observed with a double scatter gamma-ray telescope flown on a balloon over Australia on Nov. 10, 1981, 31 days after a large glitch in the pulsar period. The first and second pulses were detected from single scatters in the top scintillators at energies over 0.3 MeV with statistical significances of 1.6 sigma each, and by double scatters from all detector cell pairs at energies of 1-30 MeV with significance of 4.8 sigma and 3.8 sigma. The phase separation of the two pulses is 0.43 + or - 0.02 at the same absolute phases previously found by SAS2 and COS B for energies over 35 MeV.

Tumer, O. T.↗

NASA NTRS1983

Gamma rays of 1-30 MeV from the Vela Pulsar PSR 0833-45

Results are reported for observations of gamma rays of 1-30 MeV from the Vela Pulsar PSR 0833 - 45 carried out with the UCR double scatter gamma ray telescope on a balloon launched from Alice Springs, Australia on November 10, 1981. An integrated flux of (5.3 + or - 1.3) x 10 to the -4th photons/sq cm/s is found for the Vela region above 2 MeV. This value, together with those for the energy intervals of 2-4, 4-7, and 7-15 MeV are in reasonable agreement with the power law found by COS-B at energies above 50 MeV. A sky contour map of the fluxes is shown.

Tumer, T.↗

NASA NTRS1983

Gamma rays from the Crab Pulsar 0531+21

Results are reported for observations of PSR 0531 + 21 performed with a gamma ray double Compton scatter telescope launched on a balloon. The operation of the telescope and the handling of the data are described. Phase diagrams for the pulsar and energy distributions for gamma rays from the primary and secondary pulses are shown and discussed. The results indicate that these observations are the first of gamma ray lines from neutrons captured on protons or iron in pulsars. Arguments supporting this interpretation are given.

Long, J. L.↗

NASA NTRS1983

Gamma rays of 1-30 MeV from the Galactic Center Region

Preliminary results are reported for gamma rays from the Galactic Center Region at 1-30 MeV made with a balloon-borne double Compton scatter gamma ray telescope. The Compton scatter angle, energy, and arrival time of the incident gamma ray and direction of the Compton scattered secondary for downward-moving gamma rays were measured. The handling of the data is described, and the results of Monte Carlo simulation angular resolutions and absolute efficiencies for different zenith angles of incident gamma rays are given. A contour sky map of the weighted fluxes for a southern sky region is shown whose primary feature is a significant enhancement in the Galactic Center Region. It is concluded that several discrete sources contribute to broaden the maximum in the horizontal or RA direction. Less broadening is indicated along the galactic plane.

Oneill, T.↗