  PSR J1048-5832 is a Vela-like (P=123.6 ms; tau~20.3 kyr) gamma-ray pulsar
detected by Fermi, at a distance of ~2.7 kpc and with a rotational energy loss
rate dot{E}_{SD} ~2 x 10^{36} erg/s. The PSR J1048-5832 field has been observed
with the VLT in the V and R bands. We used these data to determine the colour
of the object detected closest to the Chandra position (Star D) and confirm
that it is not associated with the pulsar. For the estimated extinction along
the line of sight, inferred from a re-analysis of the Chandra and XMM-Newton
spectra, the fluxes of Star D (V~26.7; R~25.8) imply a -0.13 < (V-R)_0 < 0.6.
This means that the PSR J1048-5832 spectrum would be unusually red compared to
the Vela pulsar.Moreover, the ratio between the unabsorbed optical and X-ray
flux of PSR J1048-5832 would be much higher than for other young pulsars. Thus,
we conclude that Star D is not the PSR J1048-5832 counterpart. We compared the
derived R and V-band upper limits (R>26.4; V>27.6) with the extrapolation of
the X and gamma-ray spectra and constrained the pulsar spectrum at
low-energies. In particular, the VLT upper limits suggest that the pulsar
spectrum could be consistent with a single power-law, stretching from the
gamma-rays to the optical.
