Extreme Ultraviolet Spectroscopy of PKS 2155-304
Abstract
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. 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 ~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 α~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 10^20^ cm^-2^ 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1994
- DOI:
- 10.1086/187211
- Bibcode:
- 1994ApJ...422L..55F
- Keywords:
-
- Bl Lacertae Objects;
- Extreme Ultraviolet Radiation;
- Ultraviolet Spectroscopy;
- X Ray Astronomy;
- Absorption Spectra;
- Astronomical Spectroscopy;
- Extreme Ultraviolet Explorer Satellite;
- Power Spectra;
- Astrophysics