The nature of the infrared counterpart and of the optical nebula associated with the Central Compact Object in Vela Jr.

The X-ray source CXO J085201.4-461753 in the few kyr-old Vela Jr. supernova remnant (SNR, G266.2-1.2) belongs to the peculiar class of isolated neutron stars dubbed `Central Compact Objects' (CCOs). At variance with the other CCOs, which are only detected in the X-rays, CXO J085201.4-461753 has been possibly detected also at other wavelengths. In particular, a candidate near-infrared counterpart (H = 21.6 ± 0.1) was detected by the Very Large Telescope (VLT) in addition to a 6 arcsec-wide nebula detected in Hα, interpreted as a velocity-driven bow shock. Here, we present new near-infrared and optical VLT observations of the candidate counterpart to CXO J085201.4-461753 and its nebula to confirm the proposed associations. Moreover, we used archival Chandra observations to measure for the first time the CXO J085201.4-461753 proper motion. The comparison between the two sets of near-infrared VLT images, taken 10.56 yr apart, do not show evidence of proper motion for the candidate counterpart to CXO J085201.4-461753, expected from its 4 arcmin offset from the SNR geometrical centre, with a 3σ upper limit of ∼10 mas yr^-1. This is much smaller than the expected proper motion of ∼50-100 mas yr^-1, which, in turn, is below the 3σ upper limit of ∼300 mas yr^-1 that we obtained with Chandra. At the same time, VLT spectroscopy resolved the nebula optical emission, which is dominated by the N II doublet at 6548 and 6584 Å and not by Hα. To summarize, we conclude that the proposed near-infrared counterpart is likely unassociated with CXO J085201.4-461753 and that the nebula is not a velocity-driven bow shock.