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SN 2021hem - an apparently "hostless" supernova in Hercules

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Robin Leadbeater's picture
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SN 2021hem - an apparently "hostless" supernova in Hercules

Supernova SN 2021hem, currently mag 16.5 and rising appears to be hostless.

The redshift of the nearest bright galaxy, LEDA 57095 approximately matches that of the supernova as measured from the spectrum but  is several arcminutes away. Spectrum here

Cheers

Robin

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Hostless?

Hmm, I wonder if it is akin to SN1987A? I doubt that the LMC would be readily visible at that distance.

Robin Leadbeater's picture
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deep images

Yes you would need a very deep image to be sure but the two  confirmed hostless examples here

https://arxiv.org/pdf/1505.03407.pdf

are at significantly higher redshifts than this one so it should be possible to determine if it is truly hostless given time on a big telescope.

(There is no sign of anything in the DSS, SDSS 2Mass images)

Cheers

Robin

Robin Leadbeater's picture
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LMC at z=0.035

I just did a quick back of envelope check based on the LMC.  using 0.9 integrated v mag and 50kpc distance gives an absolute magnitude of ~-17.5. At a distance of 150Mpc (z=0.035) this would give an apparent magnitude of ~ 18.5 which would be easily visible in the SDSS image

Cheers

Robin

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LMC at z=0.035

Thanks.

Yes, very easily visible. I've imaged galaxies in that sort of range.

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V = 16.17 +/- 0.09 on April

V = 16.17 +/- 0.09 on April 12.

Telescope 0.5 m f/6.8 Corrected Dall-Kirkham with f/4.5 Focal Reducer
Camera  FLI PL11002M

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Robin Leadbeater's picture
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absolute magnitude

This one also looks to be at maximum

https://alerce.online/object/ZTF21aaqwjlz

Assuming the z = 0.035 in TNS estimated from the classification spectrum equates to 150Mpc distance, this puts the absolute V magnitude at  -19.7, about right for a typical type Ia with no extinction