Engineering topics
Publications and source records attributed to Niel, M..
Between October 4, 1992, and August 1, 1993, concurrent coverage by the Compton Gamma-Ray Observatory (CGRO), Mars Observer (MO), and Ulysses spacecraft, was obtained for 78 Gamma-Ray Bursts (GRBs).
We report on the results of a search for the radio counterpart to the bright gamma-ray burst of 1994 March 1. Using the Dominion Radio Astrophysical Observatory Synthesis Telescope sensitive, wide-field radio images at 1.4 GHz and 0.4 GHz were made of a region around GRB 940301. A total of 15 separate radio images were obtained at each frequency, sampling a near-continuous range of post-burst timescales between 3 and 15 days, as well as 26, 47, and 99 days. We place an upper limit of 3.5 mJy on a fading/flaring radio counterpart at 1.4 GHz and 55 mJy at 0.4 GHz. Unlike past efforts our counterpart search maintains high sensitivity over two decades of post-burst time durations. Time-variable radio emission after the initial gamma-ray burst is a prediction of all fireball models, currently the most popular model for gamma-ray bursts. Our observations allow us to put significant constraints on the fireball parameters for cosmological models of gamma-ray bursts.
We introduce the method of 'network synthesis,' which allows the detection of very weak gamma-ray transient signals in the data of the Ulysses gamma-ray burst (GRB) experiment from repeating sources. It consists of defining a grid of alpha, delta values, and for each BATSE detection of a burst from a soft gamma repeater, predicting the arrival time of the burst at Ulysses and co-adding the Ulysses data rephased so that the burst signals are aligned in time and produce a detectable pulse. We demonstrate that this method identifies the position of the soft repeater SGR 1806-20, and apply it to the repeater B1900+14. We show that the counterpart to this burst source is probably in or in the vicinity of the Galactic supernova remnant G42.8+0.6.
We compare the characteristics of 35 gamma-ray bursts (GRBs) detected simultaneously by Phebus aboard Granat and the Ulysses GRB experiment. Phebus observes a medium to high energy range (100 keV - 100 MeV), while the Ulysses GRB detector is sensitive to lower energy photons (25 - 150 keV). Comparison of the peak counts recorded by these two instruments shows that the variation in burst intensities is more extended for Phebus (above approximately 150 keV) than for Ulysses GRB. This result confirms similar observations from other instruments (Atteia et al. 1991; Mitrofanov et al. 1992; Belli 1992). We discuss the consequences of this behavior for the statistical properties of GRBs, and for the searches for a possible cosmological redshift.
A gamma-ray burst which occurred on 1992 May 1 was observed by three spacecraft in the third interplanetary network, and rapidly localized to a small error box. The coordinates were promptly circulated to a wide astronomical community, and radio, optical, and X-ray counterpart searches were carried out. A weak X-ray source was found in the error box, and two radio sources are discovered outside the error box, but in alignment with the X-ray source. The X-ray source position contains approximately 25 optical objects down to 23d magnitude. We discuss the prospects for identifying the burster counterpart.
We have identified 28 solar flares simultaneously observed by a SIGNE detector aboard the Venera 13 and Venera 14 spacecraft and the Hard X-Ray Burst Spectrometer (HXRBS) aboard the Solar Maximum Mission (SMM), over a wide range of observing angles. Fourteen of them were also observed by the Gamma Ray Spectrometer (GRS) on SMM and were included in a study of the directivity of solar X-radiation. The SIGNE and HXRBS energy coverages overlap in the 50-500 keV range, allowing a detailed comparison of energy spectra. Using this database, we have conducted stereoscopic studies of flare hard X-ray anisotropy. It is found that the 100-500 keV directivity is less than 3, both for the entire set of 28 flares and for the 14 flares which gave evidence for directivity in the SMM GRS study. We conclude that solar flare X-ray directivity can only be marginally present in our energy/observing angle range.
We study the continuum spectral evolution of 16 gamma-ray bursts detected by the Franco-Soviet SIGNE experiment in 1981-1982 by fitting time resolved (0.5 s) spectra in count space with simple thermal bremsstrahlung and synchrotron models. We find that there is no single characteristic of spectral evolution: we see hard-to-soft, soft-to-hard, luminosity-hardness tracking, and chaotic evolution. We perform correlation studies between instantaneous burst intensity and spectral temperature for seven bursts. While we basically confirm the existence of a correlation between these variables as originally claimed by Golenetskii et al. (1983) we find higher values and a broader range of correlation indices.
We analyze duration and brightness distributions of both the SIGNE Venera 13 and 14 and Burst and Transient Source Experiment (BATSE) gamma-ray burst databases. Choosing T(sub 50) as a measure of the burst duration and using both 64 and 1024 ms peak count rates, we search for correlations between duration, peak brightness, and the ratio V identically equals C(sub 64)/C(sub 1024), proposed as a measure of variability by Lamb, Graziani, & Smith. The duration histogram for SIGNE shows a long-duration peak that is consistent with BATSE, but does not exhibit the short population, instead appearing flat below 0.6 s; the difference is presumably caused by the failure of SIGNE to detect the short, faint bursts that were observed by BATSE. Estimating the instantaneous brightness by C(sub 64), we find that SIGNE confirms the BATSE result that the long and short bursts have similar maximum instantaneous brightnesses. Scatterplots between duration, brightness, and V are consistent for both databases; we show that SIGNE confirms the BATSE observation that there is a lack of bursts that are both bright over 1024 ms and contain a short, bright spike.
Upper limits to gamma-ray fluxes produced in conjunction with a radio pulsar glitch are presented. The glitch occurred on the Vela pulsar on December 24, 1988 and was the first to be observed as it occurred. Sensitive gamma-ray burst detectors aboard the Phobos 2 spacecraft were operating at this time, but recorded no significant burst at the time of the glitch. It is concluded that if a gamma-ray burst was generated in the energy range to which the Phobos detectors were sensitive, and if it was not beamed away from the spacecraft, the efficiency of glitch energy conversion into gamma-rays could not have exceeded 10 exp -4.
The scientific objectives of the Ulysses solar X-ray/cosmic gamma-ray burst experiment, and the unique features of the Ulysses mission which will help to achieve them are described. After a discussion of the special design constraints imposed by the mission, the sensor systems, consisting of two CsI scintillators and two Si surface barrier detectors covering the energy range 5-150 keV are described. Their operating modes and inflight performance are also given.
The new interplanetary gamma-ray burst network will determine source fields with unprecedented accuracy. The baseline of the Ulysses mission and the locations of Pioneer-Venus Orbiter and of Mars Observer will ensure precision to a few tens of arc seconds. Combined with the event phenomenologies of the Burst and Transient Source Experiment on Compton Observatory, the source locations to be achieved with this network may provide a basic new understanding of the puzzle of gamma ray bursts.
Twelve short cosmic gamma-ray bursts were observed during July-December, 1983. The results of the localization of this source on the basis of Prognoz-9 and ICE data are presented. The source is situated 10 deg away from the Galactic Center. These localizations indicate that the January 7, 1979 burst originated from the same 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 kT's 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.
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.
Several short (less than 40 s) solar hard X-ray events (greater than 100 keV) have been observed simultaneously with identical instruments on the Venera 11, 12, 13, and 14 and Prognoz 7 (Franco-Soviet Signe experiments) spacecraft. High time resolution (equal to or greater than 2 ms) data were stored in memory when a trigger occurred. The observations reported here were made by Prognoz 7 and V12 which were closer to the sun at the time and provided good statistics. Observations of modulation with a period of 1.6 s for the event on 1978 December 3 are presented. Also presented is evidence for fast time fluctuations from an event on 1979 November 6, observed with Venera 12, and another on 1981 September 6, observed with the Solar Maximum Hard X-Ray Burst Spectrometer. Power spectrum analysis, epoch folding, and Monte Carlo simulation to evaluate the statistical significance of persistent time delays between features. The results are discussed in light of the MHD model proposed by Zaitsev and Stepanov (1982) and Zaitsev, Stepanov, and Chernov (1984).
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.
Preliminary results of an examination of the Ondrejov and Sonneberg plate collections for possible optical counterparts to gamma-ray bursters are presented. The investigation proceeds in three different directions: (1) time-correlated searches for gamma-ray bursts (GRB) with known positions, (2) time-correlated searches for GRB without know positions, and (3) archival searches. 3 GRB with known positions and 28 GRB without known positions were studied in this way; archival searches representing a total exposure of 2.75 yr were done for 10 GRB positions, with limiting magnitudes for a 1 s flash between 3 and 8. No evidence for true optical images associated with GRB was found. Some statistical conclusions are drawn and the results obtained are discussed.
Six Einstein observations of five gamma-ray burst sources are presented and discussed. With one possible exception, no point source was detected in any of the observations. The data are interpreted in the framework of neutron star models for gamma bursters. Upper limits are derived for the surface temperatures of the neutron stars assumed to be responsible for the bursts. It is shown that the lack of soft X-ray emission may impose stringent constraints on accretion rates onto neutron stars.