Gamma-ray Burst Experiments Research Articles

Kevin C. Hurley (1942–2021)

Hurley was known for his discovery of transient repeating gamma ray bursts, which are now identified as Magnetars. He also was the principal investigator for the solar and cosmic gamma-ray burst experiment aboard NASA’s Ulysses mission.

The Ulysses Catalog of Solar Hard X-Ray Flares

Ulysses was launched in October 1990, and its Solar X-ray/Cosmic Gamma-Ray Burst Experiment (GRB) has provided more than 13 years of uninterrupted observations of solar X-ray flare activity. Due to the large variation of the relative solar latitude and longitude of the spacecraft orbit with respect to the Earth, the perspective of the GRB instrument often differed significantly from that of X-ray instruments on Earth-orbiting satellites. During extended periods the GRB experiment made direct observations of flares on the hidden face of the Sun, providing a unique record of events not visible to other instruments. The small detector area of GRB and its optimization for very high counting rates minimized the effects of pulse pile-up. We interpret the spectra, time histories, and occurrence distribution patterns of GRB data in terms of “thermal feed-through”, the confusion of thermal soft X-rays and non-thermal hard X-rays. This effect is a systematic problem for scintillation-counter spectrometers observing the solar hard X-ray spectrum. This paper provides a definitive catalog of the Ulysses X-ray flare observations and discusses various features of this unique database. For the equivalent GOES range X2 – X25, we find a power-law fit for the (differential) occurrence frequency at >25 keV with slope −1.61±0.04, with no evidence for a downturn at the highest event magnitudes (for the relatively small sample of such events available in this study). If the nine most intense events are excluded because of concerns about the effects of pulse pile-up, the slope steepens to −1.75±0.08.

A broad energy range wide field monitor for next generation gamma-ray burst experiments

A coded mask instrument based on Silicon Drift Detectors coupled to scintillators operated with a pulse shape discrimination technique is presented as a candidate wide field monitor for forthcoming gamma-ray burst (GRB) search missions. Such an instrument would allow an energy range extended from 1keV to 1MeV, in a single compact device, providing both a significant detection efficiency for the softest GRB (X-ray flashes), and the sensitivity to high energy necessary to constrain GRB spectral parameters.

Stereoscopic observations of the giant hard X-ray/gamma-ray solar flare on 1991 June 30 at 0255 UT

The hard X-ray/gamma-ray (HXR/GR) impulsive burst on 1991 June 30 (0255 UT) was associated with a flare which occured between 2 and 12 behind the east limb of the Sun. The partially occulted HXR/GR emission from this flare was detected at up to 100 MeV by three instruments on Earth-orbiting spacecraft: the Burst and Transient Source Experiment (BATSE) and the Energetic Gamma-Ray Experiment (EGRET) on CGRO and by the Payload for High Energy Burst Spectroscopy (PHEBUS) on GRANAT. As seen from the two spacecraft in Earth orbit, the size of the burst corresponds to that of a moderate electron-dominated GR event (Dingus et al. 1994; Vilmer et al. 1999). However, this event is one of the giant flares reported by Kane et al. (1995). It was observed by the Solar X-ray/Cosmic Gamma-Ray Burst Experiment (GRB) on Ulysses, located 135 east of the Earth-Sun line. GRB measured the total>28 keV HXR emission from the flare. In this paper we combine HXR observations by GRB and BATSE in order to determine the time evolution of the power-law index of the photon spectrum of the partially occulted HXR emission seen by BATSE and of the fraction R of the partially occulted to the total>28 keV emission. decreased from 5.4 to 2.6 and R varied from 20% at the beginning of the event down to<1% at its maximum. These results indicate that the spatial distribution of the HXR sources was complex, and evolved in the course of the event. While the HXR emission detected by GRB was almost entirely produced at the footpoints of loops by thick-target interactions, a fraction of the HXR emission seen by BATSE likely originated in the unocculted, low density, portion of the HXR emitting loops. The data also show that a small fraction (10%) of the HXR emission detected by BATSE in Earth orbit was radiated by a thick-target source on the visible disk.

Konus Catalog of Soft Gamma Repeater Activity: 1978 to 2000

Observational data on the bursting activity of all five known soft gamma repeaters (SGRs) are presented. This information was obtained with Konus gamma-ray burst experiments on board Venera 11-14, Wind, and Kosmos 2326 in the period from 1978 to 2000. These data on rates, time histories, and energy spectra of repeated soft bursts, obtained with similar instruments and collected together in a comparable form, should be useful for further studies of SGRs.

Present and future gamma-ray burst experiments

Gamma-ray burst counterpart studies require small, prompt error boxes. Today, there are several missions which can provide them: BeppoSAX, the Rossi X-Ray Timing Explorer, and the 3rd Interplanetary Network. In the near future, HETE-II, a possible extended Interplanetary Network, and INTEGRAL will operate in this capacity. In the longer term future, a dedicated gamma-ray burst MIDEX mission may fly. The capabilities of these missions are reviewed, comparing the number of bursts, the rapidity of the localizations, and the error box sizes.

Stereoscopic Observations of Solar Hard X‐Ray Flares Made byUlyssesandYohkoh

The Solar X-Ray/Cosmic Gamma-Ray Burst Experiment aboard the interplanetary spacecraft Ulysses has provided extensive observations of solar hard X-ray flares from a variety of angles with respect to the Sun-Earth line. During the period 1991 October-1993 June, Ulysses observed 13 flares that were also observed by the X-ray instruments aboard the Japanese satellite Yohkoh located near Earth. At least 12 flares were in full view of both the spacecraft. Eight flares, for which hard X-ray spectra were available, are examined to determine the directivity of the 20-125 keV hard X-ray sources in solar flares. They include one flare for which the view angles of Ulysses and Yohkoh were 80° and 25°, respectively. No evidence of systematic directivity was found within the uncertainty (a factor of ~2) of these measurements. These and other observations of directivity at higher energies are consistent with a nearly isotropic distribution of energetic electrons in most solar flares.

Energy Release and Dissipation during Giant Solar Flares

view Abstract Citations (46) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Energy Release and Dissipation during Giant Solar Flares Kane, S. R. ; Hurley, K. ; McTiernan, J. M. ; Sommer, M. ; Boer, M. ; Niel, M. Abstract The Solar X-Ray/Cosmic Gamma-Ray Burst Experiment aboard Ulysses has observed 11 solar hard X-ray flares with effective peak counting rates greater than 4 × 105 counts s-1. We have estimated the energy dissipated during these "giant" flares (GOES class > X12). The flare on 1991 June 1, probably the largest flare of the present solar activity cycle (cycle 22), may represent energy dissipation by greater than 20 keV electrons at a rate of ∼1032 ergs s-1, a rate of energy release ∼1000 times larger than that in the well-studied flares in 1972 August. The total energy released during the flare would then have been ∼1034 ergs carried by ∼1041 electrons with energies above 20 keV, assuming a nonthermal interpretation, or ≲ 2 × 1033 ergs assuming a thermal interpretation. The energy release rate in the other giant flares could have been 1030-1031 ergs s-1. The resources of an active region seem to be inadequate for the production of these energies. It is suggested that the instability that triggers the energy release during a solar flare may affect the corona globally (rather than only locally). Although our energy estimates are subject to large uncertainties, they may be confirmed by future Ulysses observations. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/187927 Bibcode: 1995ApJ...446L..47K Keywords: SUN: FLARES; SUN: X-RAYS; GAMMA RAYS; ACCELERATION OF PARTICLES full text sources ADS |

Upper limits to Jovian hard X radiation from the Ulysses Gamma Ray Burst Experiment

We describe the first in situ search for Jovian X radiation with a dedicated X ray instrument. Upper limits to Jupiter's X ray power in the 27‐48 keV range are presented using data taken by the gamma ray burst experiment on the inbound Ulysses trajectory, at distances between 163 and 110 RJ. The data were analyzed using three methods for detection of (1) a steady flux, (2) a flux linked to System III rotation, and (3) a sporadic flux. The 3σ upper limits lie between 1.1 × 108 and 5.6 × 108 W. The results are consistent with the idea that the bulk of the Jovian UV auroral emissions are due to energetic electrons, while the previously observed low‐energy X radiation is due to ion precipitation.

Initial results from the solar flare X-ray observations with ulysses

The Solar X-Ray/Cosmic Gamma-Ray Burst Experiment aboard the Ulysses spacecraft measures hard X-ray spectra in the nominal energy range 15–150 keV, which can be changed by ground command. Since the experiment turn-on on 11 November 1990, it has recorded hard X-ray emission from ∼100 solar flares of GOES soft X-ray class > M and several hundred smaller flares. Some of these flares were also observed by comparable instruments aboard other interplanetary and near-Earth spacecraft such as Pioneer Venus Orbiter (PVO), Yohkoh and Compton Observatory (formerly GRO), thus providing a stereoscopic view of the hard X-ray sources in those flares. This paper presents a brief description of the Ulysses instrument and some early observational results.

Are repeaters responsible for gamma-ray burst average V/V(max) less than 0.5?

We show that gamma-ray bursts, observed by the Konus experiment on Venera 11 and Venera 12, from the three identified sources of short-term repeating bursts have a very low average V/V(max) of only 0.17 +/- 0.10 and are very important contributors to the low average V/V(max) of 0.43 +/- 0.03 found from the entire Konus burst sample. We further point out that the expected number of additional, as yet unidentified, repeating sources is quite sufficient to account for the low Konus average V/V(max), assuming that the average V/V(max) for bursts from all other sources is 0.5. Thus we suggest that the class of short-term repeating gamma-ray burst sources, as yet only partially identified, are a high-luminosity population that could be responsible for the values of average V/V(max) less than 0.5 also found by the BATSE, SMM, and other gamma-ray burst experiments. We note, however, that repeating bursts cannot as yet be identified solely by their spectral and temporal properties.