Spectroscopic Classification of PSN J07583010-1421150 as a Post-Maximum Type Ia Supernova
ATel #6738; M. L. Graham, W. Zheng, B. E. Tucker, K. I. Clubb, and A. V. Filippenko (UC Berkeley)
on 23 Nov 2014; 19:31 UT
Credential Certification: Melissa Lynn Graham (melissalynngraham@gmail.com)
Subjects: Optical, Supernovae
A CCD spectrum (range 380-960 nm) of PSN J07583010-1421150 (see http://www.cbat.eps.harvard.edu/unconf/followups/J07583010-1421150.html and http://www.rochesterastronomy.org/supernova.html#PSNJ07583010-1421150 ) was obtained with the 10-m Keck I telescope (+ LRIS) on Nov. 20 UT, and classification was performed using Superfit (Howell et al. 2005, ApJ, 634, 1190). The object is a post-maximum Type Ia supernova, with a best fit to SN 1999aa at +51 days. Note that SN 1999aa was peculiar, resembling SN 1991T at earlier times (e.g., Garavini et al. 2004, AJ, 128, 387), but transitioning to a normal SN Ia a few weeks past maximum brightness; without earlier-phase spectra for the SN in NGC 2501, it may have been a normal SN Ia. The spectrum exhibits two strong components of Na I D absorption, at redshift z = 0.007 (equivalent width = 0.35 nm) and at z = 0 (EW = 0.11 nm). Based on Poznanski et al. (2012, MNRAS, 426, 1465), EW = 0.11 nm suggests that E(B-V) = 0.27 mag, but this is significantly stronger than expected from the line-of-sight Galactic extinction: A_V = 0.34 mag, or E(B-V) = 0.11 mag with R_V = 3.1 (Schlegel et al. 1998, ApJ, 500, 525). Thus, the z = 0 component of Na I D might actually be blueshifted in the rest frame of NGC 2501, in which case its velocity is approximately -2000 km/s.
