  Aims: We performed deep optical observations of the field of an old,
fast-moving radio pulsar PSR B1133+16 in an attempt to detect its optical
counterpart and a bow shock nebula.
  Methods: The observations were carried out using the direct imaging mode of
  FORS1 at the ESO VLT/UT1 telescope in the B, R, and H_alpha bands. We also
used archival images of the same field obtained with the VLT in the B band and
with the Chandra/ACIS in X-rays.
  Results: In the B band we detected a faint (B=28.1+/-0.3) source that may be
the optical counterpart of PSR B1133+16, as it is positionally consistent with
the radio pulsar and with the X-ray counterpart candidate published earlier.
Its upper limit in the R band implies a color index B-R <0.5, which is
compatible with the index values for most pulsars identified in the optical
range. The derived optical luminosity and its ratio to the X-ray luminosity of
the candidate are consistent with expected values derived from a sample of
pulsars detected in both spectral domains. No Balmer bow shock was detected,
implying a low density of ambient matter around the pulsar. However, in the
X-ray and H_alpha images we found the signature of a trail extending ~4"-5"
behind the pulsar and coinciding with the direction of its proper motion. If
confirmed by deeper studies, this is the first time such a trail has been seen
in the optical and X-ray wavelengths.
  Conclusions: Further observations at later epochs are necessary to confirm
the identification of the pulsar by the candidate's proper motion measurements.
