Optical observations of PSR J0205+6449

PSR J0205+6449 is an X-ray and radio pulsar in supernova (SN) remnant 3C 58. We report on observations of the central region of 3C 58 using the 4.2-m William Herschel Telescope at the Isaac Newton Group of Telescopes, La Palma, with the intention of identifying the optical counterpart of PSR J0205+6449 and characterizing its pulsar wind nebula (PWN). Around the pulsar position, we identified extended emission with a magnitude of B= 23.97 ± 0.10 mag, V= 22.95 ± 0.05 mag and R= 22.15 ± 0.03 mag consistent with a PWN. From the R-band image, we identified three knots with mR= 24.08 ± 0.07 mag (o1), 24.15 ± 0.07 mag (o2) and 24.24 ± 0.08 mag (o3). We confirm the presence of an optical PWN around PSR J0205+6449 and give an upper limit of mR≈ 24 for the optical magnitude of the pulsar. Furthermore, we make the tentative suggestion that our object o1, with an mR≈ 24.08, is the optical counterpart. If confirmed, the pulsar would have an LR/LX≈ 0.004 and an optical efficiency of about five per cent of the Crab pulsar. Such a low efficiency is more consistent with the characteristic age of the pulsar rather than that of SN 1181.