We report the analysis of the first superburst from a transiently accreting neutron star system with the All-Sky Monitor ( ASM ) on the Rossi X-ray Timing Explorer .
The superburst occurred 55 days after the onset of an accretion outburst in 4U 1608-522 .
During that time interval , the accretion rate was at least 7 % of the Eddington limit .
The peak flux of the superburst is 22 to 45 % of the Eddington limit , and its radiation energy output is between 4 \cdot 10 ^ { 41 } and 9 \cdot 10 ^ { 41 } erg for a distance of 3.2 kpc .
Fits of cooling models to the superburst light curve indicate an ignition column depth between 1.5 \cdot 10 ^ { 12 } and 4.1 \cdot 10 ^ { 12 } g cm ^ { -2 } .
Extrapolating the accretion history observed by the ASM , we derive that this column was accreted over a period of 26 to 72 years .
The superburst characteristics are consistent with those seen in other superbursting low-mass X-ray binaries .
However , the transient nature of the hosting binary presents significant challenges for superburst theory , requiring additional ingredients for the models .
The carbon that fuels the superburst is thought to be produced mostly during the accretion outbursts and destroyed in the frequent type-I X-ray bursts .
Mixing and sedimentation of the elements in the neutron star envelope may significantly influence the balance between the creation and destruction of carbon .
Furthermore , predictions for the temperature of the neutron star crust fail to reach the values required for the ignition of carbon at the inferred column depth .