Optical and radio behaviour of the BL Lacertae object 0716+714 ⋆

摘要: Eight optical and four radio observatories have been intensively monitoring the BL Lac object 0716+714 in last years: 4854 data points collected UBVRI bands since 1994, while light curves extend back to 1978. Many of these data, which all together constitute widest database available on this object, are presented here for first time. Four major outbursts were observed at beginning 1995, late 1997, end 2000, fall 2001. In particular, an exceptional brightening 2.3 mag 9 days was detected R band just before BeppoSAX pointing October 30, 2000. A big outburst lasted from early 1998 1999. The long-term trend shown by seems vary with a characteristic time scale about 3.3 years, longer period 5.5–6 years characterize variations. general, colour indices only weakly correlated brightness; clear spectral steepening during least one long-lasting dimming phase. Moreover, spectrum became steeper after $\rm JD \sim 2\,451\,000$, change occurring decaying phase late-1997 outburst. flux behaviour different frequencies is similar, but variation amplitude decreases increasing wavelength. index varies brightness (harder when brighter), fluxes seem be sum two different-spectrum contributions: steady base level harder-spectrum variable component. Once removed, variations appear as essentially achromatic, similarly behaviour. Flux higher lead lower-frequency ones week–month scales. quite different, broad not corresponding faster cross-correlation analysis indicating weak correlation long lags. However, minor enhancements simultaneous flares can recognized, may imply that mechanism producing strong increases also marginally affects one. On contrary, process responsible does affect emission.