  We present the results of a 17 ks Chandra ACIS-S observation of the nearby
dwarf spiral galaxy NGC 4395. Chandra affords the first high-quality, broadband
X-ray detection of the active nucleus of this object that is uncontaminated by
nearby sources in the field. We find the nuclear X-ray source to be unresolved
and confirm the rapid, large-amplitude variability reported in previous
studies. The light curve appears to show ~ 11 cycles of a quasi-periodic
oscillation with a period of ~ 400 s. If associated with an orbital feature
near the innermost stable orbit of the accretion disk, this period would
constrain the black-hole mass to be M < 9e5 M_sun. The X-ray spectrum indicates
absorption by an ionized medium, and the spectral shape appears to vary over
the course of our observation. Contrary to prior reports, however, the spectral
variations are uncorrelated with changes in the hard X-ray flux. It is possible
that the short-term spectral variability we observe results from column density
fluctuations in the ionized absorber. A power-law fit to the spectrum above 1
keV yields a photon index of Gamma ~ 0.6, much flatter than that typically
observed in the spectra of Seyfert 1 galaxies. We have ruled out photon pile-up
as the cause of the flat spectrum. Even when complex spectral features are
considered, the photon index is constrained to be Gamma < 1.25 (90%
confidence). Comparing our results with previous determinations of the photon
index (Gamma = 1.46 and 1.72), we conclude that the slope of the primary
continuum varies significantly on time scales of a year or less. The extreme
flatness and dramatic long-term variability of the X-ray spectrum are
unprecedented among active galactic nuclei.
