Models for superbursts from neutron stars involving carbon shell flashes predict that the mass accretion rate should be anywhere in excess of one tenth of the Eddington limit .
Yet , superbursts have so far only been detected in systems for which the accretion rate is limited between 0.1 and 0.25 times that limit .
The question arises whether this is a selection effect or an intrinsic property .
Therefore , we have undertaken a systematic study of data from the BeppoSAX Wide Field Cameras on the luminous source GX 17+2 , comprising 10 Msec of effective observing time on superbursts .
GX 17+2 contains a neutron star with regular Type-I X-ray bursts and accretes matter within a few tens of percents of the Eddington limit .
We find four hours-long flares which reasonably match superburst characteristics .
Two show a sudden rise ( i.e. , faster than 10 s ) , and two show a smooth decay combined with spectral softening .
The implied superburst recurrence time , carbon ignition column and quenching time for ordinary bursts are close to the predicted values .
However , the flare decay time , fluence and the implied energy production of ( 2–4 ) \times 10 ^ { 17 } erg g ^ { -1 } are larger than expected from current theory .