The Vela pulsar in the near-infrared

We report on the first detection of the Vela pulsar in the near-infrared with the VLT/ISAAC in the Js and H bands. The pulsar magnitudes are $J_{\rm s}=22.71\pm0.10$ and $H=22.04\pm0.16$. We compare our results with the available multiwavelength data and show that the dereddened phase-averaged optical spectrum of the pulsar can be fitted with a power law $F_\nu \propto \nu^{-\alpha_\nu}$ with $\alpha_\nu = 0.12\pm0.05$, assuming the color excess $E_{B-V}=0.055\pm0.005$ based on recent spectral fits of the emission of the Vela pulsar and its supernova remnant in X-rays. The negative slope of the pulsar spectrum is different from the positive slope observed over a wide optical range in the young Crab pulsar spectrum. The near-infrared part of the Vela spectrum appears to have the same slope as the phase-averaged spectrum in the high energy X-ray tail, obtained in the $2{-}10$ keV range with the RXTE . Both of these spectra can be fitted with a single power law suggesting their common origin. Because the phase-averaged RXTE spectrum in this range is dominated by the second X-ray peak of the pulsar light curve, coinciding with the second main peak of its optical pulse profile, we suggest that this optical peak can be redder than the first one. We also detect two faint extended structures in the 1$5{-}3$1 vicinity of the pulsar, projected on and aligned with the south-east jet and the inner arc of the pulsar wind nebula, detected in X-rays with Chandra . We discuss their possible association with the nebula.