2006CBET..724....1W

L. Watson, D. DePoy, and J. L. Prieto, Ohio State University; and P. M. Garnavich, University of Notre Dame, report that optical spectra (range 380-730 nm) of 2006mp (cf. CBET 720) and 2006mq (cf. CBET 721) were obtained with the Hiltner 2.4-m telescope (+ CCDS spectrograph) at MDM Observatory on Nov. 6.1 and 6.5 UT. The spectrum of 2006mp is blue and shows features typical of a type-Ia supernova before or at maximum light, although the Si II (635.5 nm at rest) and S II "W" (546.8 and 563.3 nm at rest) features are weak compared with normal type-Ia supernovae at early phases. After comparing it with library spectra from the literature, the spectrum is found to be very similar to that of the overluminous type-Ia supernova 1991T (Phillips et al. 1992, A.J. 103, 1632) at maximum light. The best match is found to occur when the spectrum of 1991T is redshifted by (1+z) = 1.023, which implies an approximate recession velocity for the host galaxy (MCG +08-31-29) of 6900 km/s.

The spectrum of 2006mq shows conspicuous absorption/emission P-Cyg features with broad absorption minima at 442, 479, 506, 569, 603, 628, and 698 nm (rest wavelength), assuming a recession velocity for the host galaxy, ESO 494-G26, of 968 km/s (Theureau et al. 1998, A.Ap. Suppl. 130, 333). The spectrum resembles the spectra of type-I supernovae around two weeks after maximum. A type-Ia supernova matches well the overall shape of the spectrum, with the main difference being the presence of a strong double absorption in 2006mq at 603 and 628 nm (rest) instead of the single absorption typically present in type-Ia supernovae at these epochs. Some type-Ib/c supernovae show the double feature at 1-2 weeks after maximum, which has been potentially identified with H_alpha and He I at high velocity (e.g., Elmhamdi et al. 2006, A.Ap. 450, 305; Branch et al. 2006, PASP 118, 791). In particular, the spectrum of the type-Ic supernova 1990B (Matheson et al. 2001, A.J. 121, 1648) at 13 days after maximum is a reasonable match to that of 2006mq. Thus, 2006mq is most likely a type-Ia supernova around two weeks after maximum, but the possibility of this object being a type-Ib/c supernova cannot be completely ruled out. The interstellar absorption feature Na I D is also detected, and an equivalent width of 0.2 nm is measured, implying a very high Galactic extinction in the line-of-sight of E(B-V)_Gal > 0.4 magnitude (Munari and Zwitter 1997, A.Ap. 318, 269), consistent with the value given by the reddening maps of Schlegel et al. (1998, Ap.J. 500, 525): E(B-V)_Gal = 0.42 mag.