Early-Phase Spectra of “Hypernova” SN 2002[CLC]ap[/CLC]

The spectral evolution of the peculiar SN Ic 2002ap during the first 40 daysis presented. The spectra display very broad absorption features, which aretypical of "hypernovae". The maximum expansion velocity measured on theearliest spectra exceeds 3 times 10^4 km s^{-1}. The spectrum of SN 2002ap atthe epoch of maximum brightness resembles that of SN 1997ef more than that ofSN 1998bw. The spectral evolution of SN 2002ap proceeds at about 1.5 times therate of SN 1997ef. The parameterized supernova spectrum synthesis code SYNOWwas used to perform line identification and deduce velocity information fromthe early-phase spectra, which are heavily affected by line blending. Thephotospheric velocity, as deduced from the fitting results and from theblueshift of the \ion{Si}{2} lambda 6355 absorption minimum, is lower than inpreviously studied hypernovae. At advanced epochs, the \ion{Si}{2} lambda 6355absorption minimum becomes difficult to distinguish. This may be caused by thegrowth of [\ion{O}{1}] lambda lambda 6300, 6364 emission. Together with therapid spectral evolution, this suggests that SN 2002ap should enter the nebularphase sooner than previously studied hypernovae.Comment: 9 pages, 4 figures, accepted for publication in ApJ Letter