Simultaneous X-Ray, Ultraviolet, and Optical Observations of the BL Lacertae Object PKS 2155-304
Abstract
X-ray observations of PKS 2155-304, performed at nine epochs in 1983-1985 with the EXOSAT satellite, are reported. The source was observed quasi-simultaneously in the far-UV with IUE, and in the optical and infrared with ESO telescopes. X-ray light curves with 400 s time resolution are derived. On two occasions the flux showed a rapid regular rising with a doubling time ~ 1 hr. Spectral fits performed on X-ray data averaged over each observation yield the following results. The medium energy data (1-10 keV) are well fitted by single power laws plus absorption, with energy index between 1.5 and 2. Marginal evidence for an absorption edge at ~ 7 keV is found in the best exposed spectrum. If we combine the ME data with those obtained with the low energy telescope (0.1-2 keV), evidence for some spectral depression at ~ 1 keV is found. This may be modeled with an edge at 660+/-26 eV with optical depth τ = 1.8 +/- 0.2. The quasi-simultaneous ultraviolet and optical data allow the reconstruction of the energy distribution on several occasions. In all cases but one, the optical, UV, and X-ray intensities are correlated. However, the variability amplitudes decrease, and the time scales increase, with decreasing frequency. These results are indicative of a synchrotron origin for the X-rays and of distinct, but connected, emission regions for the X-ray, ultraviolet, and optical bands.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1989
- DOI:
- 10.1086/167532
- Bibcode:
- 1989ApJ...341..733T
- Keywords:
-
- Bl Lacertae Objects;
- Light Curve;
- Ultraviolet Spectra;
- X Ray Sources;
- Exosat Satellite;
- Iue;
- Spectrum Analysis;
- Synchrotron Radiation;
- Temporal Resolution;
- Astrophysics;
- BL LACERTAE OBJECTS;
- GALAXIES: INDIVIDUAL ALPHANUMERIC: PKS 2155-304;
- X-RAYS: SOURCES;
- ULTRAVIOLET: SPECTRA