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Paper: Fast Optical Photometry of the BL Lac Object PKS 2155-304
Volume: 159, BL Lac Phenomenon
Page: 137
Authors: Mantegazza, Luciano; Treves, A.
Abstract: PKS 2155-304 is the brightest and best monitored BL Lac at the optical and UV wavelengths. Significant variability in this spectral region on time sales from years down to a few hours has been commonly observed in this source. Recent studies have shown that extremely rapid (time scales of ~1 hour or less) optical and UV flux variability can occur. We have undertaken a program of systematic intensive optical monitoring of PKS 2155-304 in search of fast variability events. Intensive CCD photometric monitoring in the V band accomplished at the ESO 0.91m Dutch telescope in October 1996 during ten days shows a 20% decrease of the flux in two days, followed by a similar increase and a subsequent further fading, which determined an oscillating behavior of the light curve. Intranight variability mostly follows the daily trend. Results of further V and R observations of PKS 2155-304 taken in August 1997 will be also presented.
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