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possible supernova AT 2021aai in NGC 2268

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Robin Leadbeater's picture
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possible supernova AT 2021aai in NGC 2268

https://www.wis-tns.org/object/2021aai

mag 18.7 at discovery but could reach mag 13 (plus extinction) if type Ia

Robin
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Just south of a field star

Here's an image of it from Jan 12.9. It is a difficult object to measure since there is a 17th mag star around 3 arcsec north of it. I get 17.9 tonight.

Robin Leadbeater's picture
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well done for splitting

Well done for splitting it from the nearby star. I put the spectrograph slit on it but it is so messy round there, it is going to have to outshine the star and galaxy background if I am going to have any chance.

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Yes, I thought this one would

Yes, I thought this one would be a challenge. It had a whole galaxy to go off in and it did it next to a relatively bright field star! How big is the slit you use and can you orient it to avoid that star?

Robin Leadbeater's picture
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23 microns

The slit is 23 microns or 3 arcsec. It normally runs in the Dec direction which is probably the best bet as the star and PSN will lie at different positions along the slit provided the seeing and guiding is good enough to split them. I could just pick up a weak spectrum of the pair with perhaps signs of a broad H alpha emission line  which would indicate a type II, though there is quit a bit of that around in the galaxy background as well. No split though (and to be honest at mag 17.9 I would not stand much of a chance of getting a useable spectrum in any case) 

Robin Leadbeater's picture
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levelled out

It looks like it has levelled out, well (~5 mag) short of what a type Ia without extinction would reach

https://alerce.online/object/ZTF21aadoizf

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What's going on?

Do you have any guesses / good ideas about what it might be, Robin?

Robin Leadbeater's picture
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subluminous or high extinction?

Well the distance to NGC2268 is probably reasonably accurate as it based on Ia supernova 1982B (which was V mag 13.5 when discovered just past maximum) so assuming this object is say mag 17.5 at maximum this gives it an absolute magnitude of -14.8 There is then 0.2 mag extinction from our own galaxy giving abs mag v mag ~ -15 which is very much at the low end  but not unknown for supernovae eg

https://arxiv.org/abs/astro-ph/0112051

but if there is a lot of extinction in the host galaxy it could be higher luminosity of course.

(It could also be a foreground CV of course. We need a spectrum)

It is interesting that there has been no published professional classification yet. Maybe it is something interesting and the classification is being withheld. (Not unknown. Classifications can be submitted to TNS with an embargo)

Cheers

Robin

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Transient fever

Thanks Robin.

On the topic of atypical phenomena, others may be interested that there is a nice article on transients, written by Anna Ho, in the December 2020 issue of Scientific American. Amongst other things, she talks about SN2018gep and the famous 'cow', which spawned many strange illustrations of floating cows, AT2018cow.

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Transient update

I captured the transient this evening (2021/01/16 20:30) - it is still dimmer than the nearby field star.

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