Intranight optical variability of low-mass active galactic nuclei: a pointer to blazar-like activity

This study aims to characterize, for the first time, intranight optical variability (INOV) of low-mass active galactic nuclei (LMAGNs) which host a black hole (BH) of mass M-BH similar to 10(6)M(circle dot), i.e. even less massive than the Galactic centre BH Sgr A* and 2-3 orders of magnitude below the supermassive black holes (SMBHs, M-BH similar to 10(8)-10(9) M-circle dot), which are believed to power quasars. Thus, LMAGNs are a crucial subclass of AGNs filling the wide gap between SMBH and stellar-mass BHs of Galactic X-ray binaries. We have carried out a 36-session campaign of intranight optical monitoring of a well-defined, representative sample of 12 LMAGNs already detected in X-ray and radio bands. This set of LMAGNs is found to exhibit INOV at a level statistically comparable to that observed for blazars (M-BH greater than or similar to 10(8-9) M-circle dot) and for the gamma-ray-detected Narrow-line Seyfert1 galaxies (M-BH similar to 10(7) M-circle dot) which, too, are believed to have relativistic jets. This indicates that the blazar-level activity can even be sustained by central engines with BHs near the upper limit for intermediate-mass BHs (M-BH similar to 10(3)-10(6) M-circle dot).