Discovery of a new supernova with SALT

We are happy to report our first confirmed discovery of a supernova for the international Dark Energy Survey (DES) using the Southern African Large Telescope (SALT).  DES, which is based in Chile, has just started science operations and hopes to discover thousands of supernovae over the next five years, including many Type Ia’s that were the basis of the discovery of the acceleration of the Universe that lead to the 2011 Nobel prize in physics.

Automated computer algorithms scan each night of observations from the Blanco telescope at the Cerro Tololo Inter-American Observatory in search of things that were not there before. When it finds something new it triggers an alert. Unfortunately the great majority of these alerts are false alarms and in addition there are many interlopers: asteroids, variable stars and active galactic nuclei all mimic the signature of a supernova. To confirm whether a candidate that triggered an alert is a real supernova requires a large telescope such as SALT to take the objects “fingerprint” and identify it conclusively.

The first fingerprinting with SALT of a DES candidate happened last week. DES13C1feu as it was prosaically named, was a supernova that exploded about 780 million years ago in a galaxy far, far away. The news of the dying star traveled across the vast emptiness of space until the photons ended in the Blanco telescope, triggering an alert in the computers of the DES team and causing a cascade of events that culminated in SALT quickly fingerprinting the candidate supernova.

Figure 1 is an animated image of the supernova as it appears in the arm of one of the spirals.  As is often the case, the supernova is approximately as bright as the entire host galaxy (which is why we can see them at vast distances).

DES13C1feu_zoomed_in

News of a cosmic death 780 Million years ago: before and after animation of the supernova as it appears in one of the spiral arms of the host galaxy. (Credit M. Smith, S. Crawford, E. Kasai, DES team)

Screen shot 2013-10-18 at 7.38.06 AM

SALT spectrum of the supernova (black) compared to the best-fitting template (in red) showing that it is a Type Ic supernova at redshift 0.059 (Credit M. Smith, S. Crawford, E. Kasai)


 The “fingerprinting” process proceeds by taking a spectrum which splits the light into its constituent wavelengths. After calibration the resulting curve is compared to a database of known supernovae, allowing it to be identified and aged. The spectrum, along with the best-fitting template from the known-object database, is shown in Figure 2.

We look forward to identifying and typing many more DES candidates with SALT!

Team members  in this project include Mat Smith (previously an AIMS postdoc), Steve Crawford, Eli Kasai, Roy Maartens and Patrice Okouma. You can read the official announcement of the supernova discovery here.

UPDATE November 10 2013: We have confirmed our first Type Ia supernova with SALT, at a redshift of z=0.15.

About Bruce Bassett

@cosmo_bruce
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