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LCOGT's unique capabilities help identify supernova progenitor
In June of this year, supernova iPTF13bvn, surprised astrophysicists by revealing its parentage. To
date, Type Ib supernovae have appeared to come from nowhere. Type Ib supernovae explosions appear in
surveys, but a search back through the archived data has so far resulted in no evidence of a
progenitor, likely because they are simply too faint. A recently documented search for progenitors on
a dozen Type Ib supernovae resulted in a dozen non-detections.
Because this is the first detected progenitor for a stripped envelope supernova (SNe Ib), the research
was published in The Astrophysical Journal Letters.
Chain of Events
On June 16th, the intermediate Palomar Transient Factory (iPTF) -- a robotic supernova search run by
the California Institute of Technology -- identified a new transient source in the nearby galaxy NGC
5806 (some 73 million light years from Earth) that was not there the previous evening. Astronomers
rarely capture a supernova so soon after explosion, and so they eagerly trained their telescopes on
the new event.
Using radio, optical and spectroscopic sensors, a global team of astrophysicists led by Dr Yi Cao of
Caltech began the work of tracking and characterizing the new supernova. The team from Las Cumbres
Observatory Global Telescope, organized by D. Andrew Howell, gathered several spectra of the supernova
as it evolved using the robotic FLOYDS spectrographs on 2-meter LCOGT telescopes in Hawaii and
Australia. The LCOGT 1-meter telescope were activated by Dr. Melissa Graham to observe the SN
continuously. Dr. Stefano Valenti reduced the data in real time from both the LCOGT 1-meter telescope
network and the FLOYDS spectrograph, and worked with Caltech to analyze and characterize the data. The
LCOGT data helped categorize the event as a Type Ib.
Texas Tech astrophysicist Dr David Sand, who designed and implemented the robotic FLOYDS spectrograph,
while working at LCOGT, points out that without FLOYDS, key data would have been missed. "This
supernova was discovered when the moon was almost full. Because observing in the optical is very
difficult when the moon is so bright, most telescopes in the world are configured to observe I
n the infrared. FLOYDS is on the telescope all of the time, and since it is robotic, we can get data
at any time."
While real-time observations continued on iPTF13bvn, high-resolution images of the event were
carefully registered against Hubble Space Telescope images taken at the same location years beforehand
for other purposes. Remarkably, a star was seen in the Hubble image at the exact location of the
supernova years later, suggesting that it was the object that later exploded. Based on its brightness
and color this 'supernova progenitor' was likely a massive, young Wolf-Rayet star. These stars, named
for astronomers Charles Wolf and Georges Rayet who first described them in 1867, display strong, broad
emission lines of helium. These are stars that have lost much of their envelope, or outer layers.
Valenti adds that "when we realized that the SN was a type Ib, we were quite exited, several times we
searched in archival images for progenitors of these kind of SNe, but so far, we have never seen a
Type Ib supernovae are thought to be the explosions of massive stars that have lost their outer layers
due to a stellar wind before explosion. Observations indicate they are devoid of hydrogen, but contain
helium in the remaining outer layer of the star. They are roughly as bright as 5 billion Suns.
Valenti said scientists can take another Hubble image at the location of the supernova after it has
faded away. If the star identified as the progenitor to the supernova has disappeared, then they will
know for sure that it was the star that died. Otherwise, if the star is still there, than the
supernova came from some other object too faint for researchers to see, and the mystery continues.
The intermediate Palomar Transient Factory project, which is a scientific collaboration with
California Institute of Technology, Los Alamos National Laboratory, University of Wisconsin and
several others, performs automated surveys of night skies specifically detecting transient supernovae
events. The survey finds hundreds of new supernovae annually.
Stefano Valenti, Post. Doc, LCOGT,
t: 805 880 1600