  Gamma-ray bursts (GRBs) occurring in the local Universe constitute an
interesting sub-class of the GRB family, since their luminosity is on average
lower than that of their cosmological analogs. We aim to contribute to the
study of local bursts by reporting the case of GRB 171205A. This source was
discovered by Swift Burst Alert Telescope (BAT) on 2017, December 5 and soon
associated with a low redshift host galaxy (z=0.037), and an emerging SN (SN
2017iuk). We analyzed the full Swift, dataset, comprising the UV-Optical
Telescope (UVOT), X-ray Telescope (XRT) and BAT data. In addition, we employed
the Konus-Wind high energy data as a valuable extension at gamma-ray energies.
The photometric SN signature is clearly visible in the UVOT u, b and v filters.
The maximum emission is reached at ~ 13 (rest frame) days, and the whole bump
resembles that of SN 2006aj, but lower in magnitude and with a shift in time of
+2 d. A prebump in the v-band is also clearly visible, and this is the first
time that such a feature is not observed achromatically in GRB-SNe. Its
physical origin cannot be easily explained. The X-ray spectrum shows an
intrinsic Hydrogen column density N_H,int = 7.4(+4.1 -3.6) X 10^20 / cm^2$,
which is at the low end of the N_H,int, even considering just low redshift
GRBs. The spectrum also features a thermal component, which is quite common in
GRBs associated with SNe, but whose origin is still a matter of debate.
Finally, the isotropic energy in the gamma-ray band, E_iso = 2.18(+0.63 -0.50)
X 10^49 erg, is lower than those of cosmological GRBs. Combining this value
with the peak energy in the same band, E_p=125(+141 -37) keV, implies that GRB
171205A is an outlier of the Amati relation, as are some other low redshift
GRBs, and its emission mechanism should be different from that of canonical,
farther away GRBs.
