Discovery of the supernova 2012fw = PSN J21015899-4816259

A. Klotz (Institut de Recherche en Astrophysique et Planetologie, France) used the robotic TAROT telescope at la Silla, Chile to discover PSN J21015899-4816259 at 7" W and 2" N from the nucleus of the galaxy ESO 235- G 037.

Follow-up photometry has been performed using an archive image without the supernova as a substractive mask. Images are R filtered.
The star NOMAD-1 0417-0896679 R=14.28 is choosen as the photometric calibrator.
2012 Aug. 07.13 mag>18.6R.
2012 Aug. 10.31 mag=18.2R (prediscovery image)
2012 Aug. 19.12 mag=15.6R. (discovery image)
2012 Aug. 20.13 mag=15.5R.
2012 Aug. 21.14 mag=15.5R.
2012 Aug. 24.16 mag=15.3R.
2012 Aug. 25.18 mag=15.7R.
2012 Aug. 27.20 mag=15.3R.
2012 Aug. 29.21 mag=15.7R.
2012 Aug. 30.22 mag=15.5R.
2012 Sep. 01.24 mag=15.6R.
2012 Sep. 03.25 mag=15.5R.
2012 Sep. 05.30 mag=15.7R.
2012 Sep. 07.27 mag=15.8R.
2012 Sep. 09.27 mag=16.1R.
2012 Sep. 15.03 mag=16.4R.

Using NED data for extinction and luminosity distance, we deduce an absolute R magnitude -19.0 at the date 2012 Aug. 21. The light curve is compatible with a type Ia supernova (P. Nugent's template). The maximum of brightness may occured August 24st in R band.

Spectroscopy was obtained by F. Colas (Institut de Mecanique Celeste et de Calcul des Ephemerides Paris, France) A. Peyrot and J.P. Teng (Association de Gestion de l'Observatoire Reunionnais d'Astronomie, Les Makes, Reunion island, France) using the 60 cm telescope at Les Makes, Reunion island, France (IAU station 181). A grating filter (300 tr/mm) gives a low dispersion (48A/pix). Date of observation is 2012 Aug. 21.6. Addition of 50 images of 180s shows clearly the spectrum of PSN J21015899-4816259.

We compared the spectrum of PSN J21015899-4816259 with spectra (provided by C. Buil of various SN types. The spectrum of PSN J21015899-4816259 is very similar to that of SN 2011fe in early stage (5 days before the maximum) redshifted to z=0.0186 (the redshift of the host galaxy ESO 235- G 037). Si II lines are identified. Comparisons with type II supernovae spectra are bad.

As the absolute magnitude at the maximum of light is -19.0 and the spectrum is similar to SN 2011fe, we conclude that PSN J21015899-4816259 is of type Ia.

The red spectrum is PSN J21015899-4816259. The cyan spectrum is SN 2011fe provided by C. Buil. The blue line is the SN 2011fe spectrum convolved to the resolution of  the PSN J21015899-4816259 spectrum.