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We have obtained a 12.5 ksec image of the Hercules Cluster, A2151, with the{\it ROSAT} PSPC. Comparison of the optical and X-ray data suggest the presenceof at least three distinct subclusters in A2151. The brightest X-ray emissioncoincides with the highest-density peak in the galaxy distribution, and isbimodal. The northern subclump, distinct in position and velocity, has {\it no}detectable X-ray gas. The eastern subclump, apparent in the optical contourmap, is indistinguishable from the main clump in velocity space but is clearlyvisible in the X-ray image. X-ray spectra derived from the central peak ofemission yield a best-fit temperature of 1.6 keV. The emission coincident withthe eastern clump of galaxies is cooler, 0.8 keV, and is outside the 90\%confidence intervals of the central peak temperature. We suggest that theeastern and central subclusters have recently undergone a merger event. Thelack of X-ray emission to the north suggests that those galaxies do not form aphysically-distinct structure (i.e. they are not located within a distinctgravitational potential), but rather that they are falling into the clustercore along the filament defined by the Hercules Supercluster.Comment: To appear in the March 1995 issue of AJ, LaTeX, PostScript text and  figures available by anonymous ftp from kula.phsx.ukans.ed

Subcluster mergers and galaxy infall in A2151