Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.2102d&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #21.02D; Bulletin of the American Astronomical Society, Vol. 24, p.1154
Astronomy and Astrophysics
Astronomy
1
Scientific paper
This project presents the principal conclusions of a long series of infrared and visible observations of blazars taken from 1987-92. The data fall broadly into three classes: spectropolarimetry in the range 4000-9500A of a small sample of selected AGNs; polarimetry of a sample of a dozen blazars and some twenty low polarisation quasars (LPQs); visible and infrared monitoring and fast photometry of a sample of a dozen blazars. Representitive data are presented from each of the observational programs. The aim is to view the AGN phenomenon and, especially blazars, as a whole, using novel observational methods to look for similarities and differences between distinct classes of objects. The visible spectropolarimetric characteristics of 3C273, 3C345 and CTA102 will be discussed in detail. Observations at 8A resolution with the 4.2m William Herschel Telescope are contrasted with existing knowledge from broad band photopolarimetry of these objects. It is found that the data is in broad agreement with the predictions of synchrotron theory, but numerous problems remain. Very contrasting behavior is seen in the polarization of the spectral lines in each object and, in 3C345 it is even found that different spectral lines within the same spectrum show sharply different polarization characteristics. Observations of LPQs show that at least 50% have detectable polarization, generally of 0.5-1%. The observations suggest that there are similarities between LPQs and blazars, with good evidence of variable polarization in a number of objects. Our initial sample of objects shows that almost all LPQs with detectable polarization are Radio Quiet and/or x-ray loud. Extensive fast photometry has been performed of a number of objects, especially OJ287 (visible and infrared), Mark421 and Mark501 (infrared). Rapid variability is found to be common, whilst simultaneous UBVRIJHK observations show that fast spectral variability on time scales of an hour or less also occurs with some frequency; this last has major implications for models of the active nucleus.
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