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  • Space Radiation  (2)
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  • 1
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    EGRET/COMPTEL Observations of an Unusual, Steep-Spectrum Gamma-Ray Source (1999)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: During analysis of sources below the threshold of the third EGRET catalog, we have discovered a source, named GRO J1400-3956 based on the best position, with a remarkably steep spectrum. Archival analysis of COMPTEL data shows that the spectrum must have a strong turn-over in the energy range between COMPTEL and EGRET. The EGRET data show some evidence of time variability, suggesting an AGN, but the spectral change of slope is larger than that seen for most gamma-ray blazars. The sharp cutoff resembles the high-energy spectral breaks seen in some gamma-ray pulsars. There have as yet been no OSSE observations of this source.
    Keywords: Space Radiation
    Type: EGRET Team Papers to be Published in the Proceedings of the Fifth Compton Symposium|Sep 15, 1999 - Sep 17, 1999; Portsmouth, NH; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Multi-Wavelength Observations of 3C 273 in 1993-1995 (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: We present the results of the multi-wavelength campaigns on 3C 273 in 1993-1995. During the observations in late 1993 this quasar showed an increase of its flux for energies 〉= 100 MeV from about 2.1 x 10(exp -7) photons/sq cm.s to approximately 5.6 x 10(exp -7) photons/sq cm.s during a radio outburst at 14.5, 22 and 37 GHz. However, no one-to-one correlation of the gamma-ray radiation with any frequency could be found. The photon spectral index of the high energy spectrum changed from GAMMA(sub gamma) = (3.20 +/- 0.54) to GAMMA(sub gamma) = (2.20 +/- 0.22) in the sense that the spectrum flattened when the gamma-ray flux increased. Fits of the three most prominent models (synchrotron self-Comptonization, external inverse Comptonization and the proton initiated cascade model) for the explanation of the high gamma-ray emission of active galactic nuclei were performed to the multi-wavelength spectrum of 3C 273 . All three models are able to represent the basic features of the multi-wavelength spectrum. Although there are some differences the data are still not decisive enough to discriminate between the models.
    Keywords: Space Radiation
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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