MEREGHETTI, SandroSandroMEREGHETTIDE LUCA, AndreaAndreaDE LUCASalvetti, DavidDavidSalvettiBELFIORE MONDONI, AndreaAndreaBELFIORE MONDONIMARELLI, MARTINOMARTINOMARELLIPAIZIS, ADAMANTIAADAMANTIAPAIZISRIGOSELLI, MICHELAMICHELARIGOSELLISALVATERRA, RubenRubenSALVATERRASIDOLI, LaraLaraSIDOLITIENGO, ANDREAANDREATIENGO2020-11-092020-11-0920180004-6361http://hdl.handle.net/20.500.12386/28226We report the discovery of a flaring X-ray source 7″ from the center of the globular cluster NGC 6540 obtained during the EXTraS project devoted to a systematic search for variability in archival data of the XMM-Newton satellite. The source had a quiescent X-ray luminosity on the order of 10<SUP>32</SUP> erg s<SUP>-1</SUP> in the 0.5-10 keV range (for a distance of NGC 6540 of 4 kpc) and showed a flare lasting about 300 s. During the flare, the X-ray luminosity increased by more than a factor 40, with a total emitted energy of 10<SUP>36</SUP> erg. These properties, as well as Hubble Space Telescope photometry of the possible optical counterparts, suggest the identification with a chromospherically active binary in the cluster. However, the flare luminosity is significantly higher than what is commonly observed in stellar flares of such a short duration, leaving open the possibility of other interpretations.STAMPAenArticle10.1051/0004-6361/2018330862-s2.0-85053051278000441203600003https://www.aanda.org/articles/aa/abs/2018/08/aa33086-18/aa33086-18.html2018A&A...616A..36MFIS/05 - ASTRONOMIA E ASTROFISICA