VLT observations of the magnetar CXO J164710.2-455216 and the detection of a candidate infrared counterpart

Abstract

We present deep observations of the field of the magnetar CXOJ164710.2-455216 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 {\em Chandra} position of the magnetar, of magnitudes $\mathrm{J}=23.5\pm 0.2$, $\mathrm{H}=21.0\pm 0.1$, and ${\mathrm{K}}_{\mathrm{S}}=20.4\pm 0.1$. The K${}_{\mathrm{S}}$-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 2 $\sigma$ level), consistent with the fact that the observations were taken when CXOJ164710.2-455216 was in quiescence. At the same time, we also present colour--magnitude and colour--colour diagrams in the J, H, and K${}_{\mathrm{S}}$ 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 CXOJ164710.2-455216. Future near-infrared observations of the field, following-up a source outburst, would be crucial to confirm the association from the detection of near-infrared variability and colour evolution.

5 pages, 3 figures, accepted for publication in MNRAS

References in corpus (6)

• A Debris Disk Around An Isolated Young Neutron Star
• A VLT/FLAMES survey for massive binaries in Westerlund 1. IV. Wd1-5 - binary product and a pre-supernova companion for the magnetar CXOU J1647-45?
• The most massive progenitors of neutron stars: CXO J164710.2-455216
• Adaptive optics near-infrared observations of magnetars
• Pulse Phase-coherent Timing and Spectroscopy of CXOU J164710.2-45521 Outbursts
• VLT/NACO observations of the High-Magnetic field radio pulsar PSR J1119-6127

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