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Potentially interesting transient in NGC 4631

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Robin Leadbeater's picture
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Potentially interesting transient in NGC 4631

ATLAS have  announced an interesting transient in a nearby (4Mpc) galaxy NGC 4631.

https://www.wis-tns.org/astronotes/astronote/2021-33

It was discovered yesterday at mag 18.1 which at this distance gives an absolute magnitude of -10.  It could be a nova but this would make it at the high luminosity end. It is embedded deep in the galaxy and looking at  the discovery image it would be a  tough imaging target at the moment and well out of range of amateur spectroscopy but if it turns out to be a supernova on the rise it could get much brighter (a type Ia without extinction would reach mag 9 a this distance !)

EDIT: If it is a supernova caught early it should already be much brighter tonight

Robin

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brightening

That's a great shot Nick, particularly with that bright moon. (To much haze here. I could not even see the galaxy)  It looks like it  probably is a supernova then. It depends on extinction of course which could be high given where it is but this might end up being one of the brightest for quite a while.

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I'd marked the wrong object!

My original post, which I've deleted, marked the wrong object. The new one is correct but has a later timestamp. Robin's reply hasn't violated the rules of causality.

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:-))

I thought I was going crazy for a moment there replying to imaginary posts !

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Now up to around 16.8

Here it is from 2021-01-30T23:46:28 against a very lumpy galaxy background. Astrometry matches the quoted position to within 1 arcsec.

Robin Leadbeater's picture
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LRN

It has now been classified as a probable Luminous Red Nova.  

http://www.astronomerstelegram.org/?read=14360

I have to confess I had to look up what that was. Fascinating !

https://ui.adsabs.harvard.edu/abs/2019A%26A...630A..75P/abstract

Robin

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LRNs

That was interesting breakfast reading. The last time I imaged one of these was when V838 Mon erupted 18 years ago. CCDs were much smaller then!

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V838 Mon

I remember imaging that with my modified webcam and CCTV camera

http://www.threehillsobservatory.co.uk/astro/astro_image_37.htm

and the spectacular light echo images from the Hubble. I took over where the Hubble left off :-)

http://www.threehillsobservatory.co.uk/astro/v838Mon_anim.gif

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Really nice animation

Really nice animation although I can see the difference between Hubble and your setup...

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NCG4631

Very interesting reading, and a good picture, I've never heard of this class of nova before. I hope you manage to get a spectra, fascinating class of object.

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Information from Ron Arbour

Ron Arbour has asked me to post this message in his behalf:

The object AT2021 recently discovered in NGC 4631 has been classified as a Luminous Red Variable which is a sub group of Intermediate Luminosity Optical Transients. This group included Intermediate Luminosity Red Transients and intermediate Red Novae among others and bridged the gap between Novae and Supernovae. The first discovery and hence archetype of all these objects was discovered by an amateur and member of the Association, namely myself. A paper on the object was published in the Journal.

J.Br.Astron.Assoc. 126, 3, 2016
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SN 2008S

Yes, a very impressive achievement from Ron.

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Image from last night

I took this colur image last night in fairly average conditions - in my image it has a blueish tint of a typical supernova.

Peter

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AT2021biy in NGC 4631 - Not a supernova
For clarification, the object designated AT2021biy has not been classified as a supernova but rather a Luminous Red Nova or Luminous Blue variable:
 
The response to my communication with Andrea Pastorello, one of the authours, is as follows:  
"This is surely NOT a supernova.
I'm not sure 100% it is a LRN or an LBV-outburst, we need to follow it to precisely classify it.
It is called *red* because it becomes red (cold) very rapidly, much more rapidly than most transient types, and will reach a mid-M stellar spectral type
after a few months”.
I hope this clarifies why the object appears blue, well shown in Peter Tickner’s excellent colour image. It would be nice to see an image when the object eventually turns red. However that may be very difficult as it could be quite faint.
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not a supernova

Indeed, as I already reported

https://britastro.org/comment/10041#comment-10041

I never said it was a supernova and posted the classification as soon as it became available

Cheers

Robin

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Potentially interesting transient in NGC 4631

I think we can agree though it has indeed turned out to be a  "Potentially interesting transient in NGC 4631" 

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light curve

The light curve of some of these objects bounces back though as they redden as the reference I posted shows so it would be interesting to take a comparison image in a few months time