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Spectroscopy of MASTER SN candidate near UGC11021

ATel #3615; J. L. Prieto (Carnegie Observatories)
on 31 Aug 2011; 08:37 UT
Credential Certification: Jose L. Prieto (jose@obs.carnegiescience.edu)

Subjects: Optical, Supernovae

A low-resolution optical spectrum (range 370-920 nm; resolution 0.7nm) obtained Aug. 30.98 with the du Pont 2.5-m telescope (+WFCCD) at Las Campanas Observatory in Chile of the MASTER supernova candidate near UGC11021 (ATEL #3610) shows broad He I absorption features consistent with a type Ib supernova. Cross-correlation with a library of supernova spectra using SNID (Blondin & Tonry 2007, ApJ, 666, 1024) shows that the spectrum is most similar to normal type Ib SNe at approx. 2-3 weeks after maximum light. The redshift derived from the supernova features is consistent within the uncertainties with the redshift of UGC11021 (z=0.0173; Springob et al. 2005, ApJS, 160, 149). It is interesting to note that the supernova is at 60" from the center of its host galaxy (ATEL #3610), which implies a projected separation of ~22 kpc assuming a distance of 75 Mpc to UGC11021 (via NED, from Virgo-infall recession velocity and h=0.73). Furthermore, the spiral host (class Sb in RC3 catalog) is seen almost edge-on, and the supernova lies well outside a linear extrapolation of the optical disk, at a projected distance from the disk of ~7 kpc. This location implies that the supernova either exploded in the halo of UGC11021 or in a low-luminosity dwarf galaxy companion. All these properties resemble the Ca-rich type Ib SN 2005E (Perets et al. 2010, Nature, 465, 322), although the MASTER supernova is 2 mags brighter (approx. absolute mag -17 at discovery).