Ferraro, F. R.F. R.FerraroPallanca, C.C.PallancaLanzoni, B.B.LanzoniCadelano, M.M.CadelanoMassari, D.D.MassariDalessandro, EmanueleEmanueleDalessandroMucciarelli, A.A.Mucciarelli2020-04-142020-04-1420150004-637Xhttp://hdl.handle.net/20.500.12386/24006We report on the optical identification of the neutron star burster EXO 1745-248 in Terzan 5. The identification was performed by exploiting Hubble Space Telescope/Advanced Camera for Surveys images acquired in Director's Discretionary Time shortly after (approximately one month) the Swift detection of the X-ray burst. The comparison between these images and previous archival data revealed the presence of a star that is currently brightened by ∼3 mag, consistent with expectations during an X-ray outburst. The centroid of this object well agrees with the position, in the archival images, of a star located in the turn-off/sub-giant-branch region of Terzan 5. This supports the scenario that the companion should have recently filled its Roche Lobe. Such a system represents the prenatal stage of a millisecond pulsar, an evolutionary phase during which heavy mass accretion on the compact object occurs, thus producing X-ray outbursts and re-accelerating the neutron star. <P />Based on observations (GO 14061, GO 12933, GO 9799) with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.STAMPAenArticle10.1088/2041-8205/807/1/L12-s2.0-84934295747000357262100001https://iopscience.iop.org/article/10.1088/2041-8205/807/1/L12015ApJ...807L...1FFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation