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  • ASTROPHYSICS  (2)
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  • 1
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    Discovery of an obscured low luminosity active nucleus in the spiral galaxy NGC 4258 (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The spectra and images of the nearby jet galaxy NGC 4258 (M106) obtained with ASCA indicate presence of several distinct X-ray emission components. The emission above 3 keV is pointlike and coincident in position with the optical nucleus, exhibiting a hard (photon index approximately 1.78) and absorbed N(sub H) approximately 1.5 x 10(exp 23) cm(exp -2) spectrum. This provides clear evidence that NGC 4258 hosts an obscured active nucleus of low luminosity, about 4 x 10(exp 40) ergs s(exp -1) in 2-10 keV after removing the absorption. Iron K-line emission with an equivalent width 0.25 +/- 0.10 keV was detected. The emission below 1 keV is dominated by an extended approximately 4 min thin-thermal component with a temperature approximately 0.5 keV exhibiting atomic emission lines, possibly associated with the jet. There exists a third continuum component with an intermediate spectral hardness, which is brightest at approximately 1 min south-east of the nucleus.
    Keywords: ASTROPHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 46; 3; p. L77-L80
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The X-ray emission of 3C 273 observed with ASCA (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We report preliminary results of an Advanced Satellite for Cosmology and Astrophysics (ASCA) observation of 3C 273. There is no spectral variability within the ASCA observation, in contrast to the longer term behavior found with European X-ray Observatory Satellite (EXOSAT) and Ginga which established significant changes in the spectral index of the power-law continuum on timescales of a week or more, uncorrelated with luminosity. Comparison of the ASCA data with a simultaneous Roentgen Satellite (ROSAT) Ginga observation in 1990 December shows that while the shape of the spectrum above approximately 1 keV is essentially the same, the flux in the soft component, below approximately 1 keV, considerably weaker relative to the hard component in the ASCA observation. The 2-10 keV luminosity is at least a factor of approximately 1.5 greater in the ASCA observation than in the ROSAT/Ginga observation while the ratio of 2-10 keV luminosity to 0.4-1.0 keV luminosity increases by a factor of approximately 1.2. Thus the spectral shape of the hard component appears to be independent of the relative magnitude of the soft component and is an important constraint on emission and reprocessing models. We find no significant Fe K line-emission in this observation. The data also highlight very well some of the outstanding problems in the instrumental responses.
    Keywords: ASTROPHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 46; 3; p. L49-L53
    Format: text
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    NASA TECHNICAL REPORTS
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