source was $>0.02^{\circ}$, or during passage through the South Atlantic Anomaly, or up to 5 minutes afterwards. The PCA is a non-imaging device with a field of view of FWHM $\sim1^\circ$ and so the background which we subtract must be calculated from a model. Here we use the FTOOL routine PCABACKEST V2.0c, with the new “L7” model, to calculate the background.

The resultant 2–10 keV lightcurve is shown in the top panel of Fig. 1. Further details of the X-ray light curves and variability are given by Papadakis et al. (2000). For NGC 4051, 10 counts s$^{-1}$ (2–10 keV), from 3 PCUs, corresponds to a flux of $4 \times 10^{-11}$ ergs cm$^{-2}$ s$^{-1}$.

Optical Spectroscopy
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Optical spectroscopic observations were obtained between UT 1996 January 12 (Julian Date = JD2450095) and 1998 July 28 (JD2451022), covering three separate observing seasons. Observations were made with the Ohio State CCD Spectrograph on the 1.8-m Perkins Telescope of the Ohio State and Ohio Wesleyan Universities at the Lowell Observatory (data set A) and with the FAST spectrograph (Fabricant et al. 1998) on the 1.5-m Tillinghast Reflector of the Center for Astrophysics on Mt. Hopkins (data set B). A log of these observations is 