SN2003du: 480 days in the life of a normal type Ia supernova

Aims. We present a study of the optical and near-infrared (NIR) properties of the Type Ia Supernova (SNIa) 2003du. Methods. An extensive set of optical and NIR photometry and low-resolution long-slit spectra was obtained using a number of facilities. The observations started 13 days before B-band maximum light and continued for 480 days with exceptionally good time sampling. The optical photometry was calibrated through the S-correction technique. Results. The UBVRIJHK light curves and the color indices of SN2003du closely resemble those of normal SNe Ia. SN2003du reached a B-band maximum of 13.49 +/- 0.02 mag on JD2 452 766.38 +/- 0.5. We derive a B-band stretch parameter of 0.988 +/- 0.003, which corresponds to Delta m(15) = 1.02 +/- 0.05, indicative of a SNIa of standard luminosity. The reddening in the host galaxy was estimated by three methods, and was consistently found to be negligible. Using an updated calibration of the V and JHK absolute magnitudes of SNe Ia, we find a distance modulus mu = 32.79 +/- 0.15 mag to the host galaxy, UGC 9391. We measure a peak uvoir bolometric luminosity of 1.35(+/- 0.20) x 10(43) erg s(-1) and Arnett's rule implies that M-56Ni similar or equal to 0.68 +/- 0.14 M-circle dot of Ni-56 was synthesized during the explosion. Modeling of the uvoir bolometric light curve also indicates M-56Ni in the range 0.6- 0.8 M-.. The spectral evolution of SN2003du at both optical and NIR wavelengths also closely resembles normal SNe Ia. In particular, the Si II ratio at maximum R(Si II) = 0.22 +/- 0.02 and the time evolution of the blueshift velocities of the absorption line minima are typical. The pre-maximum spectra of SN2003du showed conspicuous high-velocity features in the Ca II H& K doublet and infrared triplet, and possibly in Si II lambda 6355, lines. We compare the time evolution of the profiles of these lines with other well-observed SNe Ia and we suggest that the peculiar pre-maximum evolution of Si II lambda 6355 line in many SNe Ia is due to the presence of two blended absorption components.