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Discovery of a Type Ia Supernova in a Faint Dwarf Galaxy

ATEL # 1856; R. Williams (Caltech); E.Y. Hsiao (UVic); A. Mahabal, S.G. Djorgovski, A.J. Drake, M.J. Graham (Caltech); M. L. Graham, C. J. Pritchet, A. Parker, S. Sadavoy, D. Balam (UVic); M. Catelan (PUC); E.C. Beshore, S.M. Larson, A. Boattini (LPL/UA); E. Christensen (Gemini Observatory);
on 27 Nov 2008; 18:11 UT
Password Certification: Andrew J. Drake (

Subjects: Optical, Nova, Supernova, Transients
Referred to by ATEL #: 1860

We have discovered a supernova in observations from CSS, Palomar 60 and the Plaskett Telescope starting from 22 Nov UT. The discovery has the following parameters:

CSS081122:094326+251021 2008-11-22 UT 10:18:11 RA 09:43:26.22 Dec 25:10:21.9 Mag 16.4 Type SN Iaz=0.027

CSS081122:094326+251021 is associated with a very faint anonymous galaxy seen in SDSS DR7 images (mags: u= 23.2, g=22.7, r=22.8, i=22.7, z=23.6). Photometric follow-up was taken with P60 on Nov 24.4 UT and provides the following colours: g-r = -0.12(+/-0.15), r-i= -0.61(+/-0.1). These values are consistent with a SN type Ia within 20 days of maximum light (Poznanski et al. 2002, PASP, 114, 833). Confirmation was obtained on Nov. 26.4 UT with the 1.82-m Plaskett Telescope of the National Research Council of Canada and shows it to be a type Ia supernova about 11 days past maximum light from SNIDs (Blondin and Tonry 2007, Ap.J. 666, 1024) with fit redshift 0.027.

Based on the supernova's redshift and SDSS r-band magnitude, the host galaxy has Mr=-12.4. Additionally, assuming a peak magnitude for SN-Ia of -19.3, combined with the discovery magnitude at 7 days past maximum light (assuming a decline rate of 0.08 mags/day), the host galaxy is found to have Mr=-12.3. This result suggests that the supernova's host galaxy is an intrinsically faint Dwarf galaxy (or an Ultra-Compact Dwarf galaxy). Supernovae in such low stellar-mass systems are expected to be rare but have recently been observed for more than a dozen spectroscopically confirmed events by CRTS and others.

For finding charts and discovery images please see:
Current candidate and confirmed SNe can be found here.
CRTS optical transients are detected and published as VOEvents in real-time at and in RSS here

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R. E. Rutledge , Editor
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