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D. Barnaby, M.T. Carini, R. Walters, M. Holcomb, K.J. Littich, C. Poteet, S.R. Smith (Western Kentucky Univ.)
In 2001 we began actively monitoring 39 BL Lac objects in the R-band. Our sample includes 18 LBLs, 15 HBLs, and 6 IBLs. We have constructed light curves for 24 BL Lacs from 4 years of observations, and we consider here the maximum variation in their flux. The LBLs as a group show significantly more variation than do the HBLs, which we expect, since a BL Lac object normally shows greater variation above its synchrotron peak than below. For the LBLs, the maximum variation is strongly correlated with increasing apparent superluminal velocity. This can be understood if their relativistic jets received a boost to the electron energy that shifted the synchrotron peak to higher energy, perhaps via injection of an energetic population of electrons on top of a quiescent one. The dependence upon the superluminal velocity implies that we should not expect to see much greater optical variation in these LBLs, since the total power that can be radiated is capped by the kinetic power contained in their jet's bulk motion. We use this to predict the maximum variation that we'd expect to see for 5 low-activity LBLs in our sample.
We thank former members of the Bell observing team, and we gratefully acknowledge support from NASA grant NAG5-8762, WKU's Applied Research Technology Program, and the Kentucky Space Grant Consortium.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.