Optical behaviour of BL Lacertae during 1997-2001: long-term, intraday and intrahour variability

Abstract

Abstract We present the results of optical observations of BL Lacertae from August 1997 to November 2001 carried out with ST-6 CCD Camera attached to the Newtonian focus of the 70-cm meniscus telescope of Abastumani Observatory. The long-term, intraday and intrahour variabilities of BL Lacertae were studied on the bases of 317 and 259 nights, respectively. The variability pattern shown by BL Lacertae is very complex. The maximum amplitude of the long-term variability in the B band equals 3m.0 (rms=0.03). The variation in the V and R bands are within 2m.71 (0.02) and m.53 (0.01), respectively. This means that variations are larger at shorter wavelength or the object become bluer in the active phase. It were also demonstrated that BL Lacertae shows intraday variability within 0.30 (0.02), while intrahour variability within 0.10 (0.01) magnitudes.