Showing papers by "L. Maraschi published in 1989"
TL;DR: In this paper, a series of observations at optical, UV, and X-ray frequencies of PKS 2155-304, one of the brightest BL Lac objects is reported, and spectral fits given for various epochs show that the medium energy data are well fitted by single power laws plus absorption, with energy index between 1.5 and 2.2.
Abstract: A series of observations at optical, UV, and X-ray frequencies of PKS 2155-304, one of the brightest BL Lac objects is reported. Spectral fits given for various epochs show that the medium energy data are well fitted by single power laws plus absorption, with energy index between 1.5 and 2. Marginal evidence for an absorption edge at about 7 keV is found, as is evidence for some spectral depression at about 1 keV. This may be modeled with an edge at 660 + or - 26 eV with optical depth tau = 1.8 + or - 0.2. Energy distributions on several occasions are reconstructed, and the optical, UV, and X-ray intensities are found to be correlated in all cases but one. The variability amplitudes decrease and the time scales increase with decreasing frequency. These results indicate a synchrotron origin for the X-rays and distinct but connected emission regions for the X-ray, UV, and optical bands. 46 refs.
31 citations
TL;DR: An extensive set of quasi-simultaneous, multiwavelength observations of the intermediate polar FO Aqr (H2215-086) obtained in 1983-1985 with the Exosat and IUE satellites and from La Palma Observatory are presented in this article.
Abstract: An extensive set of quasi-simultaneous, multiwavelength observations of the intermediate polar FO Aqr (H2215-086) obtained in 1983-1985 with the Exosat and IUE satellites and from La Palma Observatory are presented. The rotational 21 minute period and sideband periods due to beating with the orbital modulation are observed in the optical band and in X-rays. In particular, it is noticeable that an unusual sideband frequency at Omega(rot) + 2 Omega(orb) is present in X-rays. Variability of the spectrum with the rotation period is detected, which can be interpreted as modulation by an absorbing envelope. A possible improvement to the current orbital ephemeris, based on photometric data, is also presented. 42 refs.
3 citations
TL;DR: The BL Lacertae object PKS 0422+00 was observed with IUE (International Ultraviolet Explorer) on August 31-September 1, 1987, when the visual magnitude of the object was V = 16.2 and again about 4 months later (January 10, 1988) during an active state (V = 15.6) as discussed by the authors.
Abstract: The BL Lacertae object PKS 0422+00 was observed with IUE (International Ultraviolet Explorer) on August 31-September 1, 1987, when the visual magnitude of the object was V = 16.2, and again about 4 months later (January 10, 1988) during an active state (V = 15.6). Quasi-simultaneous optical to infrared observations allow deriving a detailed spectral flux distribution from 8 x 10 to the 13th to 2.5 x 10 the 15th Hz, for each epoch. Fits in terms of broken power laws and logarithmic parabolas are discussed. 32 refs.
1 citations