Optical flux and colour variability of blazars in the ZTF survey

ABSTRACT We investigate the temporal and colour variability of 897 blazars, comprising 455 BL Lacertae objects (BL Lacs) 442 Flat Spectrum Radio Quasars (FSRQs), selected from Roma-BZCAT catalogue, using multiband light curves Zwicky Transient Facility (ZTF DR6) survey. Assessing characteristics over ∼2 yr time-scales, we found that 18.5 per cent (84 out 455) Lacs showed a stronger bluer-when-brighter (BWB) trend, whereas 9.0 (41 redder-when-brighter (RWB) trend. The majority (70 cent) showing RWB are host galaxy dominated. For FSRQ subclass, 10.2 (45 442) strong BWB trend 17.6 (78 Hence, find more commonly follow than do FSRQs. This can be attributed to dominant jet emission in case contribution thermal accretion disc for In analysing behaviour on shorter time windows, many blazars evince partial trends or nature (or occasionally both). Some such complex behaviours observed colour–magnitude diagrams may result transitions between jet-dominated state disc-dominated vice versa.