Mysterious transient in a globular cluster

A new exciting result from EXTraS: a mysterious X-ray flare with a duration of 300s from the center of the globular cluster NGC 6540. During the flare the X-ray luminosity increased by more than a factor 40 with a total emitted energy of 1036erg.
The paper reporting the discovery has been published on the journal Astronomy&Astrophysics. You can read it here, on arXiv or here, on A&A.
You might also want to read the ESA press release (in English).