  I found one long X-ray flare from the X-ray burster GX 3+1 in almost 6 years
of observations with the RXTE All Sky Monitor (ASM). The event had a peak flux
of about 1.1 Crab (1.5-12 keV), lasted between 4.4 and 16.2 hours and exhibited
a fluence of more than about 5x10^{41} erg for a source distance of 5 kpc.
During the exponential-like decay, with an exponential decay time of 1.6 hours,
spectral softening is seen. The total ASM effective exposure time on GX 3+1 is
estimated to be around a year. The flare bears all the characteristics of the
recently discovered so-called superbursts in other X-ray burst sources.
