Optical observations of psr j0205+6449 – the next optical pulsar?

PSR J0205+6449 is a young (similar to 5400 yr), Crab-like pulsar detected in radio and at X-ray and gamma-ray energies and has the third largest spin-down flux among known rotation-powered pulsars. It also powers a bright synchrotron nebula detected in the optical and X-rays. At a distance of similar to 3.2 kpc and with an extinction comparable to the Crab, PSR J0205+6449 is an obvious target for optical observations. We observed PSR J0205+6449 with several optical facilities, including 8m class ground-based telescopes, such as the Gemini and the Gran Telescopio Canarias. We detected a point source, at a significance of 5.5 sigma, of magnitude i' similar to 25.5, at the centre of the optical synchrotron nebula, coincident with the very accurate Chandra and radio positions of the pulsar. Thus, we discovered a candidate optical counterpart to PSR J0205+6449. The pulsar candidate counterpart is also detected in the g' (similar to 27.4) band and weakly in the r' (similar to 26.2) band. Its optical spectrum is fitted by a power law with photon index Gamma(O) = 1.9 +/- 0.5, proving that the optical emission, if of non-thermal origin, is as expected for a young pulsar. The optical photon index is similar to the X-ray one (Gamma(X) = 1.77 +/- 0.03), although the optical fluxes are below the extrapolation of the X-ray power spectrum. This would indicate the presence of a double spectral break between the X-ray and optical energy range, at variance with what is observed for the Crab and Vela pulsars, but similar to the Large Magellanic Cloud pulsar PSR B0540-69