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J.T. Pollock (Appalachian State University)
Short time-scale monitoring of the BL Lacertae object ON 231 in the R-band during the declining phase of the major outburst in the spring of 1998 has revealed a series of at least four well-defined pulses of about two hours duration with increasing amplitudes of 0.04, 0.05, 0.13 and 0.24 magnitudes. These pulses were superimposed on a 0.35 magnitude decline of the base level brightness over the eight hour run of observations. Nearly 400 data points were obtained at about 70 second intervals on the night of April 24-25 at the Appalachian State University Dark Sky Observatory with the 0.8 meter telescope equipped with a Photometrics CCD system. The rms variation for the nearby check star over the eight hours was 0.004 magnitudes. Sixteen data points obtained by Massaro et al. in the five hours prior to the data presented here (using the same comparison star) reveal one and perhaps two additional, similar brightenings. Should ON 231 continue its current active state, intense observations of it, especially during the decline from any future major outburst are needed to determine the nature of this pulsational behavior should it be exhibited again.