R. W. Klebesadel

Observations of gamma-ray bursts of cosmic origin

Sixteen short bursts of photons in the energy range 0.2-1.5 MeV have been observed between 1969 July and 1972 July using widely separated spacecraft. Burst durations ranged from less than 0.1 s to ~30 s, and time-integrated flux densities from ^10~ ergs cm to ~2 X 10 ergs cm“ in the energy range given. Significant time structure within bursts was observed. Directional information eliminates the Earth and Sun as sources. Subject headings: gamma rays — X-rays — variable stars

Detection of a fast, intense and unusual gamma ray transient

An unusual transient pulse of greater than approximately 50 keV photons was detected on March 5, 1979 by the gamma-ray burst sensor network using nine space probes and satellites. Its characteristics are unlike those of the known variety of gamma-ray bursts and therefore suggest that it was formed either by a completely different origin species or in a very different manner. In a companion Letter it is identified with the LMC supernova remnant N49.

Precise source location of the anomalous 1979 March 5 gamma ray transient

Refinements in the source direction analysis of the observations of the unusual 1979 March 5 gamma-ray transient are presented. The final results from the interplantary gamma-ray burst network produce a 0.1 arcmin/sup 2/ error box. It is nested inside the initially determined 2 arcmin/sup 2/ source region of Evans et al. that identified the supernova remnant N49 in the Large Magellanic Cloud as a possible source. This smaller source location is within both the optical and X-ray contours of N49 although not positioned at either contour center.

A new type of repetitive behavior in a high-energy transient

The high-energy burster GB 790107 has been observed to repeat, on the order of 100 times, between August 13, 1978 and June 27, 1986, with most repetitions occurring in the latter part of 1983. Here, these activities are described, discussing intensity and time-of-occurrence information covering a seven-year span of International Cometary Explorer (ICE) data. Arguments for the reality of this activity and its association with the GB 790107 source are presented. A moderately precise location derived from ICE, SMM, Pioneer Venus Orbiter, and Venera 13 Signe data is given and related to the published GB 790107 location. 9 references.

Localization, time histories, and energy spectra of a new type of recurrent high-energy transient source

The detection of a recurrent high-energy transient source which is neither a classical X-ray nor a gamma-ray burster, but whose properties are intermediate between the two, is reported. The energy spectra of 12 recurrent events are found to be soft, characterized by kTs of 34-56 keV. The time histories are short with rise and fall times as fast as about 10 ms. The source location is a 0.12 sq deg region about 10 deg from the Galactic center. 21 references.

A second catalog of gamma-ray bursts - 1978-1980 localizations from the interplanetary network

A catalog of 84 gamma-ray bursts which occurred between September 14, 1978 and February 13, 1980 is presented. The data presented consist of earth crossing times, given to about the nearest second, and time histories, in the tens of keV to MeV range, for all 84 events, as well as localizations for 80 of the events. The localizations, derived from arrival-time analysis, are given as single error boxes, double error boxes, or annuli of location, and, where possible, have been compared to the Konus localizations. They range in size from less than a square arcminute to over 1000 square degrees. The fluences of the bursts cataloged are in the range 3 x 10 to the -7th ergs/sq cm and above.

Spatial structure of greater than 100 keV X-ray sources in solar flares

Steroscopic X-ray observations of the 1979 November 5 solar flares permitted the first measurements of the altitude structure of the impulsive and gradual sources of > or approx. = 100 keV X-rays. It is found that the brightness of the impulsive as well as the gradual hard X-ray sources decreases rapidly with increase in altitude above the photosphere. Most of the X-ray emission seems to originate at altitudes < or approx. =2500 km, indicating the models of hard X-ray sources with low (< or approx. =10/sup 10/ cm/sup -3/) ion density are not consistent with the observations.

Observation of an impulsive solar X-ray burst from a coronal source

New observations of the spatial, spectral, and temporal structure of an impulsive hard X-ray source in a behine-the-limb solar flare have been made with high time resolution, hard X-ray detectors aboard two spacecraft, the International Sun Earth Explorer 3 (ISEE 3) and the Pioneer Venus Orbiter (PVO), which were separated in heliographic longitude by approx.12/sup 0/.5. The principal findings are that (1) the coronal part of the X-ray source is approx.600 times less intense than the lower-altitude part of the source; and (2) the coronal X-ray observations are consistent with a power-law electron spectrum which extends down to approx.5 keV.

Stereoscopic observations of a solar flare hard X-ray source in the high corona

The vertical structure of the impulsive and gradual hard X-ray sources in high coronae and the characteristics of the impulsive soft X-ray emission are investigated on the basis of PVE, ICE, and GOES observations of the energetic flare on February 16, 1984. The average photon spectra observed by these instruments during the impulsive and gradual hard X-ray bursts are summarized. A comparison of these unocculted and partially occulted spectra shows that the sources of the impulsive hard X-ray (greater than about 25 keV) and impulsive soft X-ray (2-5 keV) emissions in this flare extended to coronal altitudes greater than about 200,000 km above the photosphere. At about 100 keV, the ratio of the coronal source brightness to the total source brightness was 0.001 during the impulsive phase and less than about 0.01 during the gradual hard X-ray burst. The sources of the gradual hard X-ray burst and gradual soft X-ray burst were almost completely occulted, indicating that these sources were located at heights less than 200,000 km above the photosphere. 47 refs.

Directivity of 100 keV-1 meV photon sources in solar flares

Stereoscopic observations of 0.1-1.0 MeV photon sources in solar flares made with spectrometers aboard the ISEE 3 (Third International Sun Earth Explorer) and PVO(Pioneer Venus Orbiter) were analyzed to determine the directivity of the photon sources and its possible dependence on photon energy. During the period 1978 October 1-1980 October 31, a total of 44 solar flares were observed simultaneously by the two instruments. Of these, 39 flares were in full view of both the instruments, the remaining five being partially occulted by the photosphere from the line of sight of at least one instrument. The view angles theta and theta of the PVO and ISEE 3 instruments with respect to the outward solar radius at the flare site varied from one flare to another and were in the range 9-88. The difference theta - theta 1 between the two view angles varied from 1 to 66. The observations of differential photon energy spectra averaged over > or = 16 s do not indicate any systematic directivity. In most flares the directivity j (theta = 90)/j(theta = 0) of 0.1-1.0 MeV photon sources is found to be < or = 2.5.