adopted thermal plasma spectrum with a temperature of $kT = 10~{\rm keV}$ (see @fransson96 and references therein), a Galactic foreground column density of $N_{\rm H} = 1.67 \times 10^{20}~{\rm cm}^{-2}$ [@dickey90] and a distance of 13.19 Mpc (§\[res:DistExt\]).

![image](sn2008in.epsi){width="18cm"}

![image](100120v_SN.ps){width="5cm"}![image](110104v_bg.ps){width="5cm"}![image](100120v_sub.ps){width="5cm"}

Optical Spectroscopic Observation {#obs:spec}
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Long-slit low-resolution spectra ($\sim$ 6 to 14 Å) in the optical range (0.33 $-$ 1.0 ) were collected at eleven phases from +7d to +143d, including five phases from the 2-m IGO, three phases from the 9.2-m HET, two phases from the 6-m BTA and one epoch from the 3.6-m NTT [^5]. A journal of spectroscopic observations is given in Table \[tab:speclog\]. The spectroscopic data acquired from IGO, NTT and HET were reduced under the IRAF environment. Bias and flat-fielding were performed on all the frames. Cosmic-ray rejection was done using the Laplacian kernel detection method [@dokkum01]. All the data obtained from the BTA were reduced using programs in the IDL software environment.

The instrumental FWHM resolution of 2-m IGO spectra as measured from the [\[\]]{}$\lambda$5577  emission skyline was found to lie between 6 and 10Å ($\sim$ 322 - 510 ). Flux calibration was done using standard spectrophotometric fluxes from @hamuy94, assuming a mean extinction 