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  • Springer  (2)
  • 1995-1999  (2)
  • 1
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract COMPTEL on board CGRO has observed a very strong (S[〉 0.3 MeV] = 2.03 × 10−4 erg cm−2), complex, and long lasting (162 s) gamma-ray burst on February 17, 1994 (GRB 940217). Temporal fluctuations occur on timescales as short as 100 ms. Hard-to-soft spectral evolution has been observed during the burst emission and also within individual peaks. The photon spectra obtained within the 6 peaks can be modelled by single power law spectra and by broken power laws with break energies at around 1 MeV. The best-fit power law slopes vary between 1.1 and 3.5 throughout the event. The burst is located at [α 2000,δ 2000] = [29.5°, 3.8°] with a 3σ error radius of 0.9°. COMPTEL does not detect any significant “post-burst” emission (as reported by EGRET) at low energies (〈 30 MeV), and our upper limits are marginally consistent with the EGRET detections. Using high energy spectral and temporal information, distance limits to GRB 940217 have been derived.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-946X
    Keywords: gamma-ray bursts: observations ; locations ; spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In its first three years of operation, the COMPTEL instrument on theCompton Gamma-Ray Observatory has measured the locations (mean accuracy ∼1°) and spectra (0.75-30 MeV) of 18 gamma-ray bursts and continues to observe new events at a rate of ∼1/month. With good angular resolution and sensitivity at MeV energies, the growing COMPTEL burst catalog is an important new piece of evidence in the on-going GRB mystery. The COMPTEL burst locations are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts indicates the possibility of repetition. The COMPTEL burst spectra are in most cases consistent with a single power law model with spectral index in the range 2–3. However, two bursts show evidence of a spectral break in the MeV range. Measurement of rapid variability at MeV energies in the stronger bursts provides evidence that either the sources are nearby (within the Galaxy) or the gamma-ray emission is relativistically beamed. We present an overview of analysis results obtained from the COMPTEL burst catalog concentrating on the search for burst repetition and the implications of highly variable MeV emission.
    Type of Medium: Electronic Resource
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