Episodic brightenings (outbursts) of X Ser. Panels a and b: DASCH photographic light curves. The short horizontal lines represent the upper limits of brightness. Panel c: stunted outburst observed by Honeycutt et al. (1998). Panels d–i: CCD V -band AAVSO andCatalina data. The error bars of the AAVSO and Catalina data mark the standard deviation of the one-day mean of brightness. Solid lines mark the fits to those parts of the decaying branches that can be considered linear. The standard deviations of these fits are included. The scales of the horizontal axes are identical for all cases except outburst 2 (panel b).