Other
Scientific paper
Jul 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984iue..prop.1905w&link_type=abstract
IUE Proposal ID #BLFDW
Other
Scientific paper
Our ME measurements of BL Lac objects to date, coordinated with observations in other frequency bands, show positive spectral curvature within the infrared to ultraviolet energy range (Worrall and Bruhweiler 1982). There is evidence that this component is synchrotron radiation. In order to fit the spectral measurements, we find that relativistic beaming is an essential ingredient of simple models not involving electron reacceleration. It is important to discover to what extent this is observationally true of all BL Lac objects, and to then compare with expectations of the distribution in Lorentz factor derived from geometrical arguments. Our sample of BL Lac objects so far numbers 5. There are 17 other BL Lac objects for which IUE observations are listed in the master catalogue. However, many of these objects are so heavily contaminated by a galactic component in the visual and near infrared that the data cannot be usefully employed for our purpose. Also, to our knowledge, the necessary nearly simultaneous coverage in the infrared and visual only exists for 6 of these 17. The near-simultaneity is a vital element, since these active galactic nuclei (AGNs) tend to exhibit different flux variability characteristics in the different available wavebands. We present a target list primarily composed of BL Lac objects, but including 3 QSOs. Conclusions from non-simultaneous multifrequency observations by Malkan and Sargent (1982) suggest that one difference between QSOs and BL Lacs is that the non-thermal infrared to ultraviolet QSO flux does not appear to exhibit curvature. We would like to investigate this more closely, with simultaneous observations. We propose to coordinate all our observations with radio, millimeter, infrared and visual wavelength coverage and have calculated time periods during which this will be possible. Final target selection from our list of visually variable objects will be based on their magnitudes just prior to shift allotment.
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