Supernova 2005af

SN 2005af, our fourth discovery, was found on 2005 February 08.22. Confirmation from IAU came on IAUC 8482. The supernova was located in the neighboring galaxy NGC 4945, more precisely at R.A 13^o 04' 44.06" and Dec -49^o 33' 59.8". Its large offset from the center of the galaxy was 407” W and 351” S. Apparent (unfiltered) magnitude was measured as 12.8 in the day of discovery; it was the brightest SN in the sky at that time.

NGC 4945 is a very close galaxy of morphological class SB(s)cd, belonging to the NGC 5128 group in the neighborhood of the Milky Way. Recent estimates indicate its distance as around 4 megaparsec, or some 13 million light years. The galaxy’s bright integrated magnitude (9.3) and large apparent dimensions (20.0 x 3.8 arcmin) have made it one of the favorite target of Southern Hemisphere’s visual observers and astrophotographers.

Spectra of SN 2005af were taken shortly after discovery (Feb 12) by Filippenko and Foley of University of California, Berkeley, using the 10-m Keck I telescope (IAUC 8484). Their analysis has demonstrated that the supernova belonged to Type II and showed well-developed P-Cygni profiles of H, Fe II, Ca II, and other species. The general appearance of the spectrum suggested the II-plateau subclass, perhaps 1 month after the explosion. Our own photometric measures appear to be consistent with that: we have estimated an absolute magnitude of roughly –15.4 in the discovery date, which indicates that the SN should have exploded quite some weeks before it was caught by BRASS.