TESTA, VincenzoVincenzoTESTAMIGNANI, RobertoRobertoMIGNANIHummel, W.W.HummelRea, N.N.ReaISRAEL, Gian LucaGian LucaISRAEL2020-11-092020-11-0920180035-8711http://hdl.handle.net/20.500.12386/28243European Organization for Astronomical Research in the Southern hemisphere under ESO programme 091.D-0071(B);Occhialini FellowshipWe present deep observations of the field of the magnetar CXO J164710.2-455216 in the star cluster Westerlund 1, obtained in the near-infrared with the adaptive optics camera NACO@VLT. We detected a possible candidate counterpart at the Chandra position of the magnetar, of magnitudes J = 23.5 ± 0.2, H = 21.0 ± 0.1 and K<SUB>S</SUB> = 20.4 ± 0.1. The K<SUB>S</SUB>-band measurements available for two epochs (2006 and 2013) do not show significant signs of variability but only a marginal indication that the flux varied (at the 2σ level), consistent with the fact that the observations were taken when CXO J164710.2-455216 was in quiescence. At the same time, we also present colour-magnitude and colour-colour diagrams in the J, H and K<SUB>S</SUB> bands from the 2006 epoch only, the only one with observations in all three bands, showing that the candidate counterpart lies in the main bulk of objects describing a relatively well-defined sequence. Therefore, based on its colours and lack of variability, we cannot yet associate the candidate counterpart to CXO J164710.2-455216. Future near-infrared observations of the field, following up a source outburst, would be crucial to confirm the association with the detection of near-infrared variability and colour evolution.STAMPAenArticle10.1093/mnras/stx25742-s2.0-85046089652000423809400025https://academic.oup.com/mnras/article/473/3/3180/4331648https://arxiv.org/abs/1708.022332018MNRAS.473.3180TFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation