The exceptional X‐ray variability of the dwarf Seyfert nucleus NGC 4395

An analysis of the X-ray variability of the low-luminosity Seyfert nucleus NGC 4395, based on a long XMM‐Newton observation, is presented. The power spectrum shows a clear break from a flat spectrum (α ≈ 1) to a steeper spectrum (α ≈ 2) at a frequency f br = 0.5‐ 3.0 × 10 −3 Hz, comparable to the highest characteristic frequency found previously in a Seyfert galaxy. This extends the measured M BH − f br values to lower M BH than previous studies of Seyfert galaxies, and is consistent with an inverse scaling of variability frequency with black hole mass. The variations observed are among the most violent seen in an active galactic nuclei to date, with the fractional rms amplitude (Fvar )e xceeding 100 per cent in the softest band. The amplitude of the variations seems intrinsically higher in NGC 4395 than most other Seyfert galaxies, even after accounting for the differences in characteristic frequencies.