Abstract　 　 
The so-called nuclear spiral in M31, consisting of ionized and neutral dusty gas clouds of typically sub-parsec sizes, shows optical emission lines characteristic of LINERs. Yet the lack of UV radiation from either an active nucleus or massive young stars makes the ionizing source of this nearest LINER a longstanding puzzle. I will present preliminary results of a multiwavelength study of the nuclear spiral, based on new and archival HST, Spitzer and Chandra observations. I will discuss the relative importance of various ionization/excitation mechanisms, in particular heating by energetic particles that are plausibly supplied by the dormant super-massive black hole. This study advances our understanding of the physical regulation of galactic circumnuclear environments.