Optical observations of PSR J0205+6449 - the next optical pulsar?

PSR J0205+6449 is a young (~5400 yr), Crab-like pulsar detected in radio and at X-ray and γ-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 ~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 5.5s, of magnitude í ~ 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 ǵ (~27.4) band and weakly in the ŕ (~26.2) band. Its optical spectrum is fitted by a power law with photon index G 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 (G 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.