Evidence for an intermediate-mass black hole and a multi-zone warm absorber in NGC 4395

We report on the results of an analysis in the X-ray band of a recent long ASCA observation of NGC 4395, the most variable low-luminosity active galactic nucleus known. A relativistically broadened iron line at similar to6.4 keV is clearly resolved in the time-averaged spectrum, with an equivalent width of 310(-90)(+70) eV. Time-resolved spectral analysis of the heavily absorbed soft X-ray band confirms the existence of a variable, multi-zone warm absorber in this source, as proposed in a previous analysis of a shorter ASCA observation. The light curve of the source is wildly variable on time-scales of hours or less, and a factor of nearly 10 change in count rate was recorded in a period of less than 2000 s. The long observation and variability of the source allowed the power density spectrum (PDS) to be constructed to an unprecedented level of detail. There is evidence for a break in the PDS from a slope of alphasimilar to1 to alphasimilar to1.8 at a frequency of around 3x10(-4) Hz. The central black hole mass of NGC 4395 is estimated to be approximately 10(4)-10(5) M-circle dot using the break in the PDS, a result consistent with previous analyses using optical and kinematical techniques.