Transient AT2018cow

[David Swan]

Hello all,

There’s been a flurry of ATELs on the transient AT2018cow / ATLAS18qqn. The object is relatively bright and is located in the constellation Hercules – so it is well placed for us.

The initial determination of the transient as a cataclysmic variable appears now to be in doubt. Certainly the published comments on the object’s spectrum are not consistent with a CV. Maybe I am wrong – and please correct me if I am.

Thoughts?

David

[Robin Leadbeater]

I have been keeping an eye on development with this one too. The reported spectra is blue and featureless which would be consistent with it being a CV. I think the speculation about it possibly being an SN comes from the fact that it is coincident in position with the galaxy and is within the brightness range expected for an SN at this distance (though the latest measurement at mag 13.8 would put it towards the top end for an SN at this distance I think.) The problem at the moment is,  because the spectrum is currently featureless and there are confusing spectral features from the galaxy there is no definitive redshift measurement yet which would conclusively prove if it is a foreground object.

Robin

[David Swan]

Thanks Robin. I didn’t know that a CV in outburst has that spectral appearance. Hopefully with further work things will get cleared up as much as possible.

[David Swan]

This object has gone ‘mainstream’, with articles in New Scientist (and the Daily Mail). The New Scientist article has a floating cow superimposed on a star field, in reference to the transient ID.

https://www.newscientist.com/article/2172351-weve-just-seen-a-huge-space-explosion-and-dont-know-what-it-is/

[Robin Leadbeater]

Reports are it is now showing spectral features of a 1c-BL supernova. There is an HCT spectrum (rectified to remove the blue continuum) linked from David Bishop’s page

http://www.rochesterastronomy.org/sn2018/sn2018cow.html

but the features are not as obvious yet compared with this one for example I called as a 1c-BL last year 

https://wis-tns.weizmann.ac.il/object/2017ixv

Robin

[David Swan]

For anyone who is interested, here is a link to a new ATEL where the authors discuss photometry and spectroscopy of this transient. Not definitively a broad-lined type Ic supernova – previously, Robin raised uncertainty about this classification too.

http://www.astronomerstelegram.org/?read=11776

[Robin Leadbeater]

Peter Somogyi has published a spectrum taken with an ALPY.  It confirms reports of an almost featureless blue spectrum but does not shed any more light on this puzzling object

http://www.spectro-aras.com/forum/viewtopic.php?f=5&t=2052

[David Swan]

In case anyone is interested, there is an article in Sky and Telescope on the mysterious ‘Cow’ transient that appeared six months ago. Therein are further links to the research literature (Open Access).

https://www.skyandtelescope.com/uncategorized/cow-celestial-event-puzzles-astronomers/

[Peter Mulligan]

Thanks for the link David. What a very interesting article, there is no doubt that the tremendous increase in light from

AT2018cow was a very powerful and unusual event, far out shining  its host galaxy CGCG 137-068 as witnessed by the central image of June 20 2018 in the Sky & Telescope article.  It seems there are quite a few theories flying around should be interesting to see what conclusions (if any?) are drawn from further observations.

Here is another link 

http://www.esa.int/Our_Activities/Space_Science/Team_of_telescopes_finds_X-ray_engine_inside_mysterious_supernova

   

[David Swan]

Evidence for a compact object in the aftermath of the extragalactic transient AT2018cow | Nature Astronomy

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