Highly reddened Type Ia supernova SN 2004ab: another case of anomalous extinction

Abstract

We present optical photometric and spectroscopic data for supernova SN 2004ab, a highly reddened normal Type Ia supernova. The total reddening is estimated as E(B − V) = 1.70 ± 0.05 mag. The intrinsic decline-rate parameter Δm15(B)true is 1.27 ± 0.05, and the B-band absolute magnitude at maximum MmaxB is −19.31 ± 0.25 mag. The host galaxy NGC 5054 is found to exhibit anomalous extinction with a very low value of RV = 1.41 ± 0.06 in the direction of SN 2004ab. The peak bolometric luminosity is derived as logLmaxbol = 43.10 ± 0.07 erg s−1. The photospheric velocity measured from the absorption minimum of the Si ii λ6355 line shows a velocity gradient of v˙ = 90 km s−1 d−1, indicating that SN 2004ab is a member of the high velocity gradient (HVG) subgroup. The ratio of the strengths of the Si ii λ5972 and λ6355 absorption lines, R(Si ii), is estimated as 0.37, while their pseudo-equivalent widths suggest that SN 2004ab belongs to the broad line (BL) type subgroup.