Engineering topics

Peterson, L. E.

Publications and source records attributed to Peterson, L. E..

At least 37 records · Page 2

NASA NTRS1981

The spectra and light curves of two gamma-ray bursts

Observations made by the Hard X-ray and Low Energy Gamma-Ray Experiment on board HEAO-1 of the spectra and light curves of two gamma-ray bursts for which localized arrival directions will become available are presented. The burst of October 20, 1977 is found to exhibit a fluence of 0.000031 + or - 0.000005 erg/sq cm over the energy range 0.135-2.05 MeV and a duration of 38.7 sec, while that of November 10, 1977 is found to have a fluence of 0.000021 + or - 0.000008 erg/sq cm between 0.125 and 3 MeV over 2.8 sec. The light curves of both bursts exhibit time fluctuations down to the limiting time resolution of the detectors. The spectrum of the October burst can be fit by a power law of index -1.93 + or -0.16, which is harder than any other gamma-burst spectrum yet reported. The spectrum of the second burst is softer (index -2.4 + or - 0.7), and is consistent with the upper index in the double power law fit to the burst of April 27, 1972.

Knight, F. K.↗

NASA NTRS1981

Centaurus A /NGC 5128/ at 2 keV-2.3 MeV - HEAO 1 observations and implications

The active-nucleus galaxy Centaurus A has been studied at 2 keV-2.3 MeV using data from the UCSD/MIT hard X-ray and low-energy gamma-ray instrument and the GSFC/CIT cosmic X-ray experiment on HEAO-1. It is found that an E exp -1.60 + or - 0.03 power law spectrum breaking to E exp -2.0 + or - 0.2 at 140 keV best describes the January and July 1978 data. The average intensity was 50% higher during the January observations. Upper limits to unresolved lines at 511 keV and 1.6 MeV were found to be 6.5 x 10 to the -4th photons/sq cm-s and 2.2 x 10 to the -4th photons/sq cm-s, respectively, at the 90% confidence level. The present data are consistent with the detailed calculations of the synchrotron self-Compton mechanism; they may also agree, marginally, with the predictions of emission from spherical accretion onto black holes.

Baity, W. A.↗

NASA NTRS1981

Hard X-ray structure of the Crab Nebula

Two-dimensional maps of the Crab Nebula have been synthesized in 22-64 keV range through the modulation collimator experiment. The effective angular resolution is about 15-arcmin. The result indicates that the Crab morphology is strictly controlled by the pulsar.

Makishima, K.↗

NASA NTRS1980

Hercules X-1 hard X-ray pulsations observed from HEAO 1

The 1.24-sec pulsations of Her X-1 in the energy range 13-75 keV have been analyzed in data obtained from the UCSD/MIT experiment on HEAO 1 during observations of the source on three dates in February 1978 and three in August 1978. Observational results are (1) the main pulse broadens somewhat with increasing energy; (2) the pulsation light curve undergoes pronounced changes at the leading edge of the main pulse from day to day; (3) spectral hardening within the main pulse is confirmed; (4) a 40-60 keV spectral feature in the spectrum is confirmed; (5) this feature is resolved, the pulse width broadening is greater than 20%, and its centroid varies with pulsation phase; and (6) the 13-75 keV spectrum does not noticeably vary from day to day, except for an overall intensity factor. Some implications of these results for the prevailing models of Her X-1 and the HZ Her-Her X-1 system are briefly discussed.

Gruber, D. E.↗

NASA NTRS1980

HEAO 1 observations of gamma-ray lines from a solar flare

HEAO 1 observed gamma radiation, including the 2.223 MeV line of deuterium and the 4.43 MeV line of C-12, from a white-light solar flare of 1978 July 11. Line strengths over a 4 minute integration were 1.00 + or - 0.29 and 0.18 + or - 0.07 photons/sq cm s, respectively, and the continuum in the 1-5 MeV range fitted a spectrum 10 E to the -3rd photons/sq cm s keV. The 2.2 MeV line lagged 94 + or - 30 s behind the gamma-ray continuum, which itself was delayed about 20 s from the hard X-ray (not less than 40 keV) and microwave fluxes. This is the second flare for which both MeV-range lines and continuum have been observed, and the first for which simultaneous white-light observations exist. The prompt gamma-ray line (4.43 MeV) can be directly interpreted as an energy deposition of not greater than 7 x 10 to the 26th ergs per sec by energetic protons at photospheric depths. This is insufficient to maintain the white-light continuum by normal photospheric emission mechanisms.

Hudson, H. S.↗

NASA NTRS1979

Observation of 2A1415+255 /NGC 5548/ by OSO-7

Results are reported for OSO 7 X-ray observations of the Seyfert galaxy NGC 5548, which has been positively identified with the X-ray source 2A1415+255, over the energy range from 5 to 350 keV. The best-fit power-law spectrum is found to have an index of 1.78 + or - 0.25 for the data from 5.4 to 100 keV. This best-fit model is used to calculate a 2-10-keV flux of (4.2 + or - 2.1) x 10 to the -10th erg/sq cm-sec on the assumption of no low-energy absorption. The observed variability is shown to imply an active region whose extent is of the order of a light year. This, in turn, implies that the bulk of the emission originates at the core of the galaxy, which would support a synchrotron self-Compton model.

Rothschild, R. E.↗

NASA NTRS1979

A search for gamma-ray spectral lines from the Galactic Center by HEAO-1

Preliminary results are reported for a search by HEAO 1 for gamma-ray lines from the Galactic Center in the energy range from 1.5 to 8 MeV. The hard X-ray/low-energy gamma-ray instrument aboard HEAO 1 is briefly described, and results are examined which indicate no obvious statistically significant spectral lines from the Galactic Center. It is concluded that the present observations fail to confirm the previously reported 4.4-MeV flux from the Galactic Center but that the existence of the reported 4.4-MeV feature cannot be strongly rejected on the basis of these results.

Matteson, J. L.↗

NASA NTRS1978

HEAO observations of X-ray bursts from MXB1730-335

The March 18, 1978 burst activity of the rapid burster MXB 1730-335 was studied by examining 58 minutes of quick-look data for the A2 and A4 experiments on HEAO 1. Very large, moderately sized, and small bursts are characterized. Type II bursts were found to show a spectral softening during burst decay. The existence of flux was sought in the 85-160 keV energy range, and it was found that the large type II bursts contain less than 5% of their total X-ray energy in this range. The implications of the lack of a hard X-ray flux with respect to accretion instability models of X-ray bursts are considered.

Hoffman, J. A.↗

NASA NTRS1978

Possible X-ray counterparts of gamma-ray sources

The results are presented of a survey regarding the X-ray source positions which fall within the error boxes of 10 unidentified gamma-ray sources observed with the aid of the COS-B satellite. In three cases, including CG 135-1, CG 312-1, and CG 327-0, an X-ray source was found within the gamma-ray error box. However, because of the large uncertainty regarding the gamma-ray source positions, the positional coincidence is not necessarily conclusive. It is, therefore, necessary to take into account additional information on the spectral or temporal characteristics of the X-ray sources. It is found that the X-ray source 4U 02416 plus 1 is a possible candidate as the X-ray-counterpart of CG 135 plus 1 in connection with both spectral hardness characteristics and positional coincidence.

Maraschi, L.↗

NASA NTRS1977

A search for hard X-rays from five strong extragalactic radio sources

Data from the University of California at San Diego (UCSD) hard X-ray instrument on OSO-7 have been used to search the regions containing 3C 390.3, M87, 3C 273, 3C 111, and 3C 129. We have a weak detection of 3C 390.3 and a possible detection of 3C 111. Sensitive upper limits on hard X-rays have been obtained for the other objects. The available observational data indicate a correlation between hard X-ray emission, self-absorbed gigahertz radio emission, and strong optical emission lines in extragalactic sources. Self-Compton X-ray models have been calculated for the sources observed in this paper, and the angular sizes, lifetimes, and B fields in these sources have been estimated. These model calculations agree with existing VLBI and time variability data.

Mushotzky, R. F.↗

NASA NTRS1977

OSO-7 hard X-ray observations of 3U 0352+30 = X Persei

Results are reported for OSO 7 observations of 3U 0352+30 (X Per) over the energy range from 7 to 110 keV. It is found that this source has either a hard power-law spectrum or a thermal bremsstrahlung spectrum over the observed energy range, indicating that X Per may be the prototype of a new class of weak galactic hard X-ray sources. The data are shown to be consistent with spectra calculated for accretion onto a degenerate dwarf of at least 1 solar mass. Geometrical and dynamical constraints are considered for a model in which an accreting degenerate dwarf is in a close orbit about the primary of X Per, and it is concluded that such a model is not ruled out at present. It is suggested that X-ray sources associated with Be stars may make a significant contribution to the diffuse hard X-ray background in the galactic plane.

Mushotzky, R. F.↗

NASA NTRS1976

New upper limits on Jovian X rays

The paper presents results of a comprehensive search for X-ray emission from the Jovian magnetosphere, using data obtained with an X-ray telescope aboard OSO 3. This satellite scanned Jupiter for 33 days from a distance of 4.4 AU during a maximum phase of solar activity. No transient X-ray fluxes were observed to accompany decameter-wave radio bursts, but upper limits on the steady X-ray emission over the energy range from 7.7 to 210 keV are estimated. These limits are shown to be consistent with the fluxes measured by Pioneer 10 as well as with the trapped-particle fluxes predicted by recent precise modeling of the Jovian trapped radiation. Upper limits are determined for the energy dissipated on Jupiter in bremsstrahlung-producing collisions and also for the electron loss rate. The energy limit is found to be approximately equal to the total solar radiant energy intercepted by the Jovian disk. It is concluded that Jovian X-rays are unlikely to be detected by near-earth observations with sensitivities currently conceivable.

Peterson, L. E.↗

NASA NTRS1976

Hard X-ray imaging facility for space shuttle: A scientific and conceptual engineering study

A shuttle-accommodated instrument for imaging hard X-rays in the study of nonthermal particles and high temperature particles in various solar and cosmic phenomena was defined and its feasibility demonstrated. The imaging system configuration is described as well as the electronics, aspect systems, mechanical and thermal properties and the ground support equipment.

Peterson, L. E.↗

NASA NTRS1976

UCSD OSO-7 observations of the hard X-ray spectrum and variability of Centaurus A

Results are reported for four X-ray scans of the region containing Cen A. It is found that the X-ray source had a hard number spectrum (spectral index of -1.2) during these observations and that the intensity in the range from 10 to 100 keV apparently increased by 230% with no detectable change in spectral shape between two observations 210 days apart. Either a Compton-synchrotron mechanism or thermal bremsstrahlung at any temperature greater than 200 keV is suggested as the source of the X-rays. It is noted that the present observations, together with a similar detection of another galaxy, may establish a distinct class of extragalactic X-ray objects with flat and highly absorbed spectra.

Mushotzky, R. F.↗

NASA NTRS1975

Hard X-ray observations of NGC 4151

The X-ray source 3U 1207 + 39, associated with the Seyfert galaxy NGC 4151, has been scanned repeatedly by the UCSD X-ray telescope on board the OSO-7 satellite. A weak source with a hard spectrum has been unambiguously detected in this region in October 1972, and with lesser statistical significance at other times between November 1971 and May 1973. The photon spectrum in the 7-110 keV range is best fitted by a power law of the form dN/dE = 0.012 E to the exponent negative 1.1 photons per sq cm per second per keV, consistent with the Uhuru measurement in the 2-6 keV range. The hard spectrum observed and very short electron lifetimes implied severely constrained nonthermal models for the emission. An extremely hot gas is also consistent with the observations.

Baity, W. A.↗

NASA NTRS1975

Observations of the Circinus X-1 region

The X-ray telescope on board the OSO-7 satellite has provided observations of the Cir X-1 region for over 110 days between December 1971 and March 1973. Although statistically significant fluctuations in the 7- to 11-keV flux were measured, no periodicities in the range between 5 hours and 100 days were found to an upper limit of about 40 percent amplitude. Intensities in the 7- to 57-keV range show variability by a factor of approximately 25 and changes in the spectral shape reflected by a number spectral index varying from about 1.1 to about 3.0. There is a positive correlation between intensity and spectral shape, with a steeper spectrum at times of peak intensity. Although power-law, exponential, and blackbody spectral shapes are equally good fits to these data alone, examination of all the available data appears to rule out a simple blackbody spectrum, at least at times of maximum intensity.

Baity, W. A.↗

NASA NTRS1975

Instrumental technique in X-ray astronomy

A detailed review of the development of instruments for X-ray astronomy is given with major emphasis on nonfocusing high-sensitivity counter techniques used to detect cosmic photons in the energy range between 0.20 and 300 keV. The present status of X-ray astronomy is summarized together with significant results of the Uhuru observations, and photon interactions of importance for the detection of X-rays in space are noted. The three principal devices used in X-ray astronomy (proportional, scintillation, and solid-state counters) are described in detail, data-processing systems for these devices are briefly discussed, and the statistics of nuclear counting as applied to X-ray astronomy is outlined analytically. Effects of the near-earth X-ray environment and atmospheric gamma-ray production on X-ray detection by low-orbit satellites are considered. Several contemporary instruments are described (proportional-counter systems, scintillation-counter telescopes, modulation collimators), and X-ray astronomical satellite missions are tabulated.

Peterson, L. E.↗

NASA NTRS1974

Observation of a cosmic gamma-ray burst on Apollo 16. I - Temporal variability and energy spectrum

A cosmic gamma-ray event occurring April 27, 1972 at 10.68 UT was observed by gamma-ray and X-ray spectrometers on Apollo 16 as well as by Vela 6A. Analysis has yielded a detailed time profile of the entire event, an energy spectrum covering three order of magnitude (2.0 to 7.9 KeV and 0.067 to 5.1 MeV) and a source location. A well-defined onset prior to the main impulse period and a probable precursor are reported. The total energy of the event over the observed range was 2 x 10 to the minus 4th power ergs/sq cm. The data indicate the presence of a hard component which persists during the entire event, with a softer variable component becoming dominant during the most explosive burst portion.

Metzger, A. E.↗