Using HST/STIS , we have detected far-ultraviolet nuclear activity in the giant elliptical galaxy NGC 1399 , the central and brightest galaxy in the Fornax I cluster .
The source reached a maximum observed far-UV luminosity of \sim 1.2 \times 10 ^ { 39 } ergs s ^ { -1 } in January 1999 .
It was detectable in earlier HST archival images in 1996 ( B band ) but not in 1991 ( V band ) or 1993 ( UV ) .
It faded by a factor of \sim 4 \times by mid-2000 .
The source is almost certainly associated with the low luminosity AGN responsible for the radio emission in NGC 1399 .
The properties of the outburst are remarkably similar to the UV-bright nuclear transient discovered earlier in NGC 4552 by Renzini et al .
( 1995 ) .
The source is much fainter than expected from its Bondi accretion rate ( estimated from Chandra high resolution X-ray images ) , even in the context of “ radiatively inefficient accretion flow ” models , and its variability also appears inconsistent with such models .
High spatial resolution UV monitoring is a valuable means to study activity in nearby LLAGNs .