Our first story of the day came out last week while we were on hiatus, and it came out with the title “The ‘Cow’ Mystery Strikes Back” and the most confusing scientist quote we’ve ever seen: “When I reduced the data, I thought I made a mistake. The ‘Koala’ resembled the ‘Cow’ but the radio emission was as bright as a gamma-ray burst!” This quote came from Anna Ho, a graduate student of astronomy at Caltech and lead author of the study. She was referring to SN 2018cow, which has an algorithmically determined name that just happens to spell ‘cow’. That particular supernova became famous for being 10-100 times more luminous than would be expected. In a paper in Nature, two competing teams came together to determine this was “either a newly formed black hole in the process of accreting matter or the frenetic rotation of a neutron star.” One of the key features of this system is an unusual blue color.
The Koala in the quote was a second object, with the license plate designation ZTF18abvkwla. Those last 4 letters, ‘kwla’, earned this object the moniker ‘Koala’. This object wasn’t called a supernova but was instead referred to as a Fast Blue Optical Transient.
Now a third object, which has no cute name, has been found: CSS161010. This object was discovered through its radio and x-ray emissions, and like the prior two events, has a fast blue optical light pattern. It was also observed to be ejecting material at a substantial fraction of the speed of light.
In astronomy, finding three objects that act the same means there is a pattern and cause to declare the discovery of a new kind of object. This new kind of object is being called a Fast Blue Optical Transient, or FBOT, and is classified as objects that look like supernovae but have a bright blue transient superimposed and may be seen to be ejecting material rapidly. This work is described in a pair of papers in the Astrophysical Journal Letters and The Astrophysical Journal, with lead authors Deanne Coppejans and Anna Ho. These papers describe the likely origins of this blue outburst being the shock wave from the supernova hitting surrounding material.
This paper was likely written without knowledge of the paper we discussed two weeks ago describing Gamma Ray Bursts (GRBs) as being the result of a binary system. This paper reflects on the prominent model of GRBs being form single star explosions with powerful jets of not understood origins. This model advocates for FBOTs being single object explosions with a surrounding disk of material that generates a jet and the blue transient light.
I honestly wouldn’t be surprised if we discovered these FBOTs are either GRBs seen at a different angle or binary systems with a different configuration than GRBs. But… we don’t actually know right now. These are early days, and I kind of feel like we’re at a point where everyone needs to take a breath and reconsider these ultra-luminous objects.
“A Mildly Relativistic Outflow from the Energetic, Fast-Rising Blue Optical Transient CSS161010 in a Dwarf Galaxy,” Deanne Coppejans et al. 2020 May 26, Astrophysical Journal Letters (Preprint on arxiv.org)
“The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at z = 0.27,” Anna Ho et al. 2020 May 26, Astrophysical Journal (Preprint on arxiv.org)