2011CBET.2866....3M

L. Magill, M. Fraser, and R. Kotak, Queen's University, Belfast; and A. Pastorello, Osservatorio Astronomico di Padova, Istituto Nazionale di Astrofisica, Universita di Padova, report that an optical spectrogram (range 390-1000 nm) of PSN J23060280+3406367 = SN 2011gu was obtained with the William Herschel Telescope (+ ACAM) on Oct. 15.01 UT. The spectrum was cross-correlated with a library of supernovae spectra using the "Gelato" code (Harutyunyan et al. 2008, A.Ap. 488, 383). The best fit was with the peculiar type-Ia supernova 1991bg at an epoch of 2 days post-maximum (Filippenko et al. 1992, A.J. 104, 1543); however, the blue end of the spectrum is relatively noisy, and the Ti II trough that characterizes the SN-1991bg sub-class does not seem to be as pronounced in 2011gu. The strength of the O I 777.4-nm feature is comparable to that of SN 1991bg. An expansion velocity of 9000 km/s is measured from the Si II absorption feature found at 635 nm, corrected for the expansion velocity of the host galaxy, NGC 7485 (5706 km/s; Wegner et al. 1993, A.J. 105, 1251; via the NED website). The authors tentatively identify a feature at the rest wavelength of NGC 7485 that is likely due to Na I D lines (equivalent width of 31.5 nm), suggesting non-negligible extinction within the host galaxy.