Discovery of the supernova 2012fr = PSN J03333599-3607377

1. Chronology of the discovery

In the Saturday afternoon 2012 October 27th, Alain Klotz (Institut de Recherche en Astrophysique et Planetologie, France) checked the galaxy images from TAROT la Silla telescope using the SN_Tarot tool in the AudeLA software.

The comparison of the night image of the galaxy NGC 1365 with a reference image taken one month before shows clearly the presence of a new star 3"W and 52"N from the nucleus of the galaxy. Note that this image was initially taken to measure the magnitude of SX Fornax for the research program of TAROT RRLyr survey

First thing done was to check if an object such an asteroid was known at this place. Nothing had been reported before.

Four individual images (exposure time 30s, unfiltered) were retrieved in the TAROT image archive. The four images show the new star. Note that clouds arrived over la Silla just after these four images.

The first rapid analysis (position R.A. = 03h33m36.1s, Decl. = -36o07'34" equinox J2000.0, magnitude 15.6U) allowed to edit a new TOCP alert. The object does not appear in an image taken 2012 Oct. 24.05 (limiting magnitude 15.8 R) neither in an image taken 2012 Oct. 19.37 (limiting magnitude 19.2 R). A TOCP follow-up was completed to give additional informations.

2012 October 28th at 6h41 UT Emmanuel Conseil sent an email to Alain Klotz indicating he took an image of NGC 1365 on 2012 Oct 27th 3h UT that shows the supernova candidate. Emmanuel Conseil used the robotic telescope Slooh in the Canaria island (image bellow). This is the first confirmation. An ATEL was posted to alert astronomers.

2012 October 28th 22h UT, Michael Childress (Australian National University) took the first spetrum and posted an ATEL indicating that it is a type Ia supernova 11 days before the maximum of light. Michael wrote: "This is really a great SN, a Ia found early in a HST Key Project Cepheid host will be very useful for the extragalactic distance scale!". Christian Buil (Castanet, France) took also another spectrum few hours later.

2012 October 31th 10h30 UT, the CBET 3275 gives the official designation 2012fr for the supernova.

2012 October 31th 11h59 UT, Jonathan.Normand (Observatoire Paris Meudon, France) retrieved an image taken with the 60cm telescope at Les Makes observatory (Reunion Island, Idian Ocean, France). This image gives a limiting magnitude of the early stage of the supernova.

2. Observation follow-up

The TAROT telescope has taken BVR (Johnson) images of NGC 1365 and NGC 1316 each night since October 29th (there was bad weather in the  28th night). Rigorous photometry reduction was done using Loneos stars in the field of NGC 1316. Preliminary light curve shows the supernova becomes bluer and bluer before the maximum. the dotted lines are standard model of SNIa from Nugent with a best fit for a date of maximum Nov. 11th. 

Spectroscopy follow-up is done by ARAS ring:

3. Data analysis

The NED database gives the following values for NGC 1365:
Luminosity Distance : 21.2 Mpc      (m-M) = 31.63 mag
Foreground extinction : Ab=0.074    Av=0.056    Ar=0.044

Then, a type Ia supernova can reach Mv=-19.3 at the maximum. So the apparent magnitude at maximum should be V = Mv + (m-M) +Av = -19.3 + 31.63 + 0.06 = 12.4

The position of the supernova over a public VLT image shows a faint object near the center of the position circle: