A supernova impostor in NGC 3362 ?

[Robin Leadbeater]

In my talk on Saturday I briefly mentioned “supernova impostors” such as Luminous Blue Variables which can have very large outbursts, occasionally mistaken for supernovae. Sometimes the error is only recognised when the “supernova” explodes for a second time !  Well it looks like Ron Arbour may have just spotted one

“Possible LBV Eruption at the site of SN2010ct”       https://wis-tns.weizmann.ac.il/astronotes/astronote/2019-2

Is it the same object wrongly identified as a supernova in 2010? Has it produced another outburst or could it have gone supernova this time. One to watch.

Robin

[Martin Mobberley]

Hi Robin,

I posted my image of Ron’s discovery on my Member page a few hours ago. However Ron has just e-mailed some rather depressing news. Ron spotted the almost identical position and so informed the TNS in a ‘follow-up’ observation that it appeared SN2010ct was in outburst and might be a LBV. HOWEVER, since then the Italian ISSP group have filed it as a new SN discovery. This means that Ron was the first to find and report full information on the object as a possible LBV, but, officially, is not the SN discoverer! Apparently the two objects are not quite in the same position so it seems to be just a horrible piece of bad luck! The TNS have apologised to Ron for this bad luck, all down to Ron’s vigilance in noting the almost identical position with SN 2010ct. Still, the similarity in position does seem hard to believe……….Ron is, understandably, gutted, as he’s checked 40,000 images since his last discovery and narrowly missed 15 SNe in the last 16 months.

Martin

[Robin Leadbeater]

I see the Zwicky Transient Facility spotted it 9 days ago but only reported it on TNS today.

https://wis-tns.weizmann.ac.il/object/2019cda

There are not so many unique amateur discoveries these days with all the robotic surveys.  I am starting to see the same with my spectroscopic confirmations as more dedicated pro spectroscopic capability comes on line. Initially when I started in 2016, most of mine were stand alone confirmations but now most of them eventually get a second pro followup spectrum. 

[Robin Leadbeater]

Hi Martin,

Thanks for the update. That is bad luck. I think in Ron’s position I would have reported it on TNS as a possible SN noting there that it appears to be coincident with SN2010ct.  If it was SN2010ct, that would mean that it was not classified correctly originally so it could have been an SN this time. It is still only a possible though so far of course until a spectrum is taken. Only 18% of possible SN submitted to TNS were confirmed last year.

I have had a look at the original confirmation CBET for SN2010ct. I must say the description of the spectrum does sound convincingly like a type II SN and not an LBV outburst.

http://ned.ipac.caltech.edu/cgi-bin/ex_refcode?refcode=2010CBET.2323A…1S

Cheers

Robin

[Robin Leadbeater]

There are now 2 pro spectra confirming it as a supernova, type 1c

[Ron Arbour]

If you enter a suspect SN’s coordinates into the TNS report form and a supernova has already been found within ~3 arc seconds of that location, it will treat your data as a follow-up observation. You cannot enter it as a “new” discovery. As my object was located less than a couple of arc second from SN 2010ct, and almost 9 years had elapsed since the event it couldn’t possibly be a follow-up observation of the same object.

Additionally, the chances of a 2nd SN exploding at an almost identical position (~2 arc seconds) in this galaxy are virtually nil so it was quite logical to think it terms of a recurrent object i.e. an new LBV Luminous Blue Variable.

The discovery of a new LBV event usually creates a lot of professional interest but, because of SN 2010ct’s position in the *archives*, several thousand of objects below the latest, it would go completely unnoticed. This why I reported the problem of LBV’s to the TNS staff a couple of years ago and one of the reasons for the creation of the new AstroNotes scheme.

On many occasions, several in the last few months, I have entered a suspect SN’s coordinates in the report form only to be informed that a report claim has already been posted for an object at the same position which means that I could claim discovery for it. This is exactly what happened in this case.

Believing the object to be an LBV which I could not enter, I sent all the relevant data directly to the TNS team just as they were going to announce the launch of AstroNotes and they suggested I use that to convey the discovery information to the community. As it happens I was the first person to use the system.

I couldn’t believe it when I saw the ISSP (Italian Supernova Search Project’s) discovery announcement on the TNS. I have since learned from the TNS staff that a new object *can* be entered for the same position if the original report is over 5 years old, now they tell me!

So, 40,000 images have been taken since my last discovery in Nov. 2017 and to miss this one after sending all the relevant data to the powers to be, leaves me somewhat displeased.

[Ron Arbour]

There was a important word omitted in my previous post, The passage should have read:

“On many occasions, several in the last few months, I have entered a suspect SN’s coordinates in the report form only to be informed that a report claim has already been posted for an object at the same position which means that I could *not* claim discovery for it. This is exactly what happened in this case.”

[Dr Andrew Smith]

You know what you achieved. Well done.

Regards Andrew 

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