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  • ASTRONOMY  (4)
  • Astronomy  (3)
  • Spacecraft Instrumentation  (1)
  • locations  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    Analysis of COMPTEL gamma-ray burst locations and spectra (1995)
    Springer
    Astrophysics and space science 231 (1995), S. 231-234 
    Details
    ISSN: 1572-946X
    Schlagwort(e): gamma-ray bursts: observations ; locations ; spectra
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00658622
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  • 2
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    The INTEGRAL scatterometer SPI (1997)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: The INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL) mission's onboard spectrometer, the INTEGRAL spectrometer (SPI), is described. The SPI constitutes one of the four main mission instruments. It is optimized for detailed measurements of gamma ray lines and for the mapping of diffuse sources. It combines a coded aperture mask with an array of large volume, high purity germanium detectors. The detectors make precise measurements of the gamma ray energies over the 20 keV to 8 MeV range. The instrument's characteristics are described and the Monte Carlo simulation of its performance is outlined. It will be possible to study gamma ray emission from compact objects or line profiles with a high energy resolution and a high angular resolution.
    Schlagwort(e): Spacecraft Instrumentation
    Materialart: ; 591-598
    Format: text
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  • 3
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    New COMPTEL results on pulsar studies at MeV energies (1997)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The Compton telescope (COMPTEL) onboard the Compton Gamma Ray Observatory (CGRO) detected the pulsar PSR B1951-32 at MeV energies, and found indications of a signal from PSR B0656+14. In the combined spectra from COMPTEL and the energetic gamma ray experiment telescope (EGRET) onboard CGRO, it can be seen that the maximum luminosities of these objects are reached in the COMPTEL energy range. These spectra can be compared with those from four other pulsars observed in MeV energies with COMPTEL. The spectral properties of five of the six pulsars, Vela, PSR B1509-58, PSR B1951-32 and PSR B0656+14, require breaks and bends at MeV energies. The sixth pulsar, the Crab pulsar, approximately follows a power law flux relation from keV to GeV energies. It is concluded that this spectral behavior may play a role in the discrimination between current gamma ray emission models.
    Schlagwort(e): Astronomy
    Materialart: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 287-290; ESA-SP-382
    Format: text
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  • 4
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    COMPTEL observations of GRO J1655-40 (1997)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The transient black hole candidate GRO J1655-40 was shown elsewhere to eject matter at apparently superluminal velocities. The oriented scintillation spectrometer experiment (OSSE) spectra, measured during the X-ray outbursts, are consistent with a single power law up to 600 keV, with no evidence of a high energy cutoff. The detection of the flaring behavior of this source up to 10 MeV was claimed elsewhere. The Compton telescope (COMPTEL) observations in the 0.75 to 30 MeV band of this source are analyzed. The upper limits on the time averaged emission are presented and gamma ray flares are searched for. It is concluded that the COMPTEL data can neither confirm nor refute the claimed detection of a large gamma ray flare from this source. The gamma ray flare search in five years' worth of data did not reveal evidence for the occurrence of strong flares on timescales of two days.
    Schlagwort(e): Astronomy
    Materialart: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 225-228; ESA-SP-382
    Format: text
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  • 5
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    New COMPTEL results on the Orion/Monoceros region (1997)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Results from recent observations of the Orion/Monoceros region, acquired with the Compton telescope (COMPTEL), are summarized, confirming previously reported results of excessive 3 to 7 MeV emission which is probably due to nuclear de-excitation lines from C-12 and O-16 nuclei following energetic nuclear interactions. The emphasis is on findings concerning the extent of the emission region. It is found that the emission extends over the entire cloud complex, although it may result from a few localized source regions. A preliminary spectrum is presented which indicates that the emission is widely spread over the 3 to 7 MeV range, suggesting a dominantly broadline origin from energetic C and O nuclei. The spectrum shows features that may be due to the splitting of the C and O lines.
    Schlagwort(e): Astronomy
    Materialart: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 71-74; ESA-SP-382
    Format: text
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  • 6
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    COMPTEL observations of Ti-44 gamma-ray line emission from Cas A (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The Compton Telescope (COMPTEL) telescope aboard the Compton Gamma-Ray Observatory (CGRO) is capable of imaging gamma-ray line sources in the MeV region with a sensitivity of the order 10(exp -5) photons/(sq cm s). During two observations periods in July 1992 and February 1993 the Galactic plane in the region of the young supernova remnant Cas A was observed, showing evidence for line emission at 1.16 MeV from the decay of Ti-44 at a significance level of approximately 4 sigma. This is the first time a supernova remnant has been detected in the gamma-ray line from Ti-44 decay. Adopting a distance of 2.8 kpc to the Cas A remnant, the measured line flux (7.0 +/- 1.7) x 10(exp -5) photons/(sq cm s), can be translated into a Ti-44 mass ejected during the Cas A supernova explosion, between (1.4 +/- 0.4) x 10(exp -4) solar mass and (3.2 +/- 0.8) x 10(exp -4) solar mass, depending on the precise value of the Ti-44 mean life time and on the precise date of the event. Implications of this result for supernova nucleosynthesis models are discussed.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 284; 1; p. L1-L4
    Format: text
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  • 7
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    Diffuse galactic continuum emission measured by COMPTEL and the cosmic-ray electron spectrum (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: Diffuse galactic continuum gamma-ray emission in the 0.75-30 MeV range from the inner Galaxy has been studied using data from COMPTEL on the Compton Gamma-Ray Observatory. Observations of the inner Galaxy from the Sky Survey have been used. The imaging properties of COMPTEL enable spatial analysis of the gamma-ray distribution using model fitting. A model based on atomic and molecular gas distributions in the Galaxy has been used to derive the emissivity spectrum of the gamma-ray emission and this spectrum is compared with theoretical estimates of bremsstrahlung emission from cosmic-ray electrons.
    Schlagwort(e): ASTRONOMY
    Materialart: The Astrophysical Journal Supplement Series (ISSN 0067-0049); 92; 2; p. 425-428
    Format: text
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  • 8
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    Gamma-ray properties of active galactic nuclei (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: Recent observations by the Compton Observatory (CGRO) have increased our knowledge about the gamma-ray emission from Active Galactic Nuclei (AGN) considerably. The three most important findings of CGRO with respect to AGNs are: first, no Seyfert 1 galaxy has been found to show emission above 500 keV. The by far strongest Seyfert 1 galaxy NGC 4151 shows a spectrum which falls off exponentially with an e-folding energy of 39 keV between 65 and 500 keV. OSSE so far has detected or has indications of detections for seven additional Seyfert 1 galaxies, which, however, all show very weak hard X-ray emission compared to NGC 4151. No annihilation feature has been seen from any Seyfert galaxy to this date. Second, the radio galaxy Cen A shows a power-law energy spectrum from hard X-ray energies of about 150 keV to at least 3 MeV. It has not been seen at EGRET-energies. Third, a new class of AGN was discovered at energies above 100 MeV by EGRET. The power of these objects in gamma-rays can dominate the luminosity in other spectral ranges. These objects are associated with extragalactic sources that have blazar properties. The high-energy gamma-ray emission is probably produced in relativistically outflowing jets. At hard X-ray energies the objects are rather weak. Spectral breaks at MeV energies were found by COMPTEL for three of these objects (3C 273, 3C 279, and PKS 0528+134).
    Schlagwort(e): ASTRONOMY
    Materialart: The Astrophysical Journal Supplement Series (ISSN 0067-0049); 92; 2; p. 593-598
    Format: text
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  • 9
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    COMPTEL gamma-ray observations of the quasars CTA 102 and 3C 454.3 (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-27
    Beschreibung: The blazar-type active galactic nuclei CTA 102 (QSO 2230+114) and 3C 454.3 (QSO 2251+158), located about 7 deg apart, were observed by the Compton Gamma Ray Observatory at four epochs in 1992. Both were detected by Energy Gamma Ray Experiment Telescope (EGRET). The combined Compton Telescope (COMPTEL) observations in the 10-30 MeV energy range clearly indicate a source of MeV emission, which is likely due to a contribution from both quasars. These observations strongly suggest that the power-law spectra measured by EGRET above approximately 50 MeV flatten at lower MeV energies. A comparison with observations at other wavelengths shows that the power spectra of CTA 102 and 3C 454.3 peak at MeV energies. This behavior appears to be a common feature of gamma-ray active galactic nuclei (AGN).
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 295; 2; p. 330-334
    Format: text
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