Supernova 2008J: early time observations of a heavily reddened SN 2002ic-like transient

Aims. We provide additional observational evidence that some Type Ia supernovae (SNe Ia) show signatures of circumstellar interaction (CSI) with hydrogen-rich material. Methods. Early phase optical and near-infrared (NIR) light curves and spectroscopy of SN 2008J obtained by the Carnegie Supernova Project are studied and compared to those of SNe 2002ic and 2005gj. Our NIR spectrum is the first obtained for a 2002ic-like object extending up to 2.2 mu m. A published high-resolution spectrum is used to provide insight on the circumstellar material (CSM). Results. SN 2008J is found to be affected by A(V) similar to 1.9 mag of extinction and to closely resemble SN 2002ic. Spectral and color comparison to SNe 2002ic and 2005gj suggests R-V < 3.1. Spectral decomposition reveals the underlying SN emission matches a 1991T-like event and, since SN 2008J is as luminous as SN 2005gj (V-max = -20.3 mag), we conclude that their CSI emissions are similarly robust. The high-resolution spectrum reveals narrow emission lines produced from un-shocked gas characterized by a wind velocity of similar to 50 km s(-1). We conclude that SN 2008J best matches an explosion of a SN Ia that interacts with its CSM.