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Extreme ultraviolet spectroscopy of PKS 2155-304

  • Fruscione, Antonella
  • Bowyer, Stuart
  • Konigl, Arieh
  • Kahn, Steven M.
Publication Date
Jan 19, 1994
DOI: 10.1086/187211
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We present the extreme ultraviolet (75-110 A) spectrum of the BL Lac object PKS 2155-304, the first spectrum of an extragalactic source obtained with the Extreme Ultraviolet Explorer (EUVE). The spectrum shows a generally smooth continuum, which can be modeled by a single power law plus interstellar absorption, and possibly an absorption feature at approximately 80 A. The best fit to the data suggests that the EUV spectrum can be interpreted as a simple extrapolation of the X-ray continuum, with an energy index alpha is approximately = 1.6; however, shallower or steeper power laws with indices between -0.4 and 2.7 cannot be ruled out by the existing EUV data alone. The data provide strong constraints on the interstellar neutral H and He along the line of sight. Using a column density of 1.36 x 1020/sq cm for the Galactic neutral hydrogen along the PKS 2155-304 line of sight, the neutral helium column density is constrained to be 9%-10% of the hydrogen amount.

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