Breathtaking Celestial Explosions Analyzed Using New Survey Techniques

Cosmic explosions detected using new techniques

Scientists have made an important leap forward in understanding the evolution of massive stars, after identifying a precursor to Type Ib supernovae. A series of findings were published in the Astrophysical Journal Letters, with research touching upon the relationship between Type 1b supernovae and Wolf-Rayet Stars, as well as high-energy Gamma-ray Bursts (GRB) and afterglow bursts.

These findings were made possible by use of the Intermediate Palomar Transient Factory (iPTF) telescope scans, which scoured the skies to capture images of cosmic explosions.

Type Ib Supernovae and Their Origins

Prior to 1985, supernovae were either placed into one of two categories – Type I or Type II. This distinction was made based upon the absorption lines that manifested in its spectrum. Type I was then later subdivided into Type Ia and Type Ib. Type Ib supernovae is a category of stellar explosion, which demonstrates helium absorption at a rest wavelength of 5876 angstroms, but lacks an absorption line for silicon and hydrogen.

Spectra for Type Ia and Type Ib and c
Spectra patterns for Type Ia and Type Ib/c supernovae

The diagram shows the typical spectra for Type Ia supernovae versus Type Ib and Type Ic supernovae. As is evident, Type Ib/c supernovae show intermediate mass elements, including magnesium, oxygen, calcium and carbon, whereas Type Ia is principally dominated by iron lines.

Supernovae are stellar explosions from massive stars, whose cores have collapsed. These massive stars are structured in the manner of an onion, with layers of different elements undergoing fusion, which are then progressively stripped away. The outermost layer, consisting primarily of hydrogen, is the first to be shed, followed by helium, carbon, neon, and so on.

According Alexei V. Filippenko of the Department of Astronomy, at the University of California, Type 1b/c supernovae could be the result of core collapses in massive stars that lose their outer helium and hydrogen layers, via solar winds or transfer to companion stars.

Wolf Rayet Star Progenitors

Scientists from the California Institute of Technology in Pasadena located the supernova, using images acquired from the Samuel Oschin Telescope 48-inch and 60-inch Telescope at the Palomar Observatory. As part of the iPTF project, the group of researchers discovered a link between Wolf-Rayet stars and Type Ib supernovae.

The iPTF research was based upon the original Palomar Transient Factory (PTF) project, which was setup in 2008 to explore supernovae, novae, extrasolar planets, compact binaries and solar system bodies, to name just a few. iPTF evolved to allow rapid follow-up of newly discovered supernovae, within hours of their detection.

Keck II and Hubble telescopes allowed composite image of supernova iptf13bvn and progenitor star
Composite image, produced using images from Keck II and Hubble space telescopes, showing the IPTF13bvn progenitor and its candidate star

The rate of discovery using iPTF has been astonishingly rapid, with two recently published papers showcasing research from iPTF astronomers; the first of which was published in September. Led by Yi Cao, of the California Institute of Technology’s Astronomy Department, the researchers managed to identify a Wolf-Rayet progenitor candidate of Type Ib supernova, iPTF13bvn.

These Wolf-Rayet progenitors are massive, evolved stars that are reported to lose their mass at a rapid pace, due to powerful stellar winds. Until most recently, there was limited evidence to link Wolf-Rayet stars as progenitors to Type Ib supernovae. However, Cao and his colleagues believe that the iPTF13bvn supernova took place in a location that was previously occupied by one of these Wolf-Rayet stars.

Using the 10-meter Keck telescopes, based in Hawaii, the group obtained accurate images of the position of the supernova. These images were then compared to those collected from the Hubble Space Telescope, back in 2005, showing the Wolf-Rayet star to have spatially coincided with the supernova.

Cao reflected upon the implications of his team’s findings in a recent press release:

“All evidence is consistent with the theoretical expectation that the progenitor of this Type Ib supernova is a Wolf-Rayet star… Our next step is to check for the disappearance of this progenitor star after the supernova fades away. We expect that it will have been destroyed in the supernova explosion.”

GRBs and Afterglow Observations

Meanwhile, a second paper, entitled Discovery and Redshift of an Optical Afterglow in 71 degrees squared: iPTF13bxl and GRB 130702A, which was published Oct. 20, used

optical transient IPTF13bxl to GRB 130702A
Image showing discovery of the optical transient IPTF13bxl / GRB 130702A: the left panel shows the location of the optical afterglow (black diamond), whilst the two right-hand panels show the sites before and after the explosion, with and without the afterglow.

Gamma-ray Burst Monitor localization to report the discovery of the afterglow of GRB 130702A. After making a series of observations, the astronomers were able to link GRB 130702A with the optical afterglow, called iPTF13bxl.

Gamma ray bursts are observed as intense flashes of gamma rays, which last anywhere between fractions of a second to several minutes in duration. They are thought to be emitted from high-energy explosions from distant galaxies, often associated with supernovae. Each GRB is followed by an afterglow, which is released as radiation with a lower wavelength than the original explosion.

GRBs are thought to be associated with rapidly rotating, massive stars. GRB 130702A was initially detected by Fermi, based upon the emission of high-energy radiation. A correlation was then drawn between GRB 130702A and the iPTF13bxl afterglow, with the fading of the GRB shortly followed by the emergence of the afterglow.

By: James Fenner

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