We report on Chandra , RXTE , Swift/BAT and MAXI observations of a \sim 1 day X-ray flare and subsequent outburst of a transient X-ray source observed in October–November 2011 in the globular cluster Terzan 5 .
We show that the source is the same as the transient that was active in 2000 , i.e. , the neutron star low-mass X-ray binary EXO 1745–248 .
For the X-ray flare we estimate a 6–11 hr exponential decay time and a radiated energy of 2 - 9 \times 10 ^ { 42 } erg .
These properties , together with strong evidence of decreasing blackbody temperature during the flare decay , are fully consistent with what is expected for a thermonuclear superburst .
We use the most recent superburst models and estimate an ignition column depth of \approx 10 ^ { 12 } g cm ^ { -2 } and an energy release between 0.1 - 2 \times 10 ^ { 18 } erg g ^ { -1 } , also consistent with expected superburst values .
We conclude therefore that the flare was most probably a superburst .
We discuss our results in the context of theoretical models and find that even when assuming a few days of low level accretion before the superburst onset ( which is more than what is suggested by the data ) , the observations of this superburst are very challenging for current superburst ignition models .