SN 2021hem – an apparently “hostless” supernova in Hercules

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  • #574935
    Robin Leadbeater
    Participant

    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

    #584049
    Paul Leyland
    Participant

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

    #584053
    Robin Leadbeater
    Participant

    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

    #584054
    Robin Leadbeater
    Participant

    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

    #584059
    Paul Leyland
    Participant

    Thanks.

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

    #584091
    Maxim Usatov
    Participant

    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

    #584092
    Robin Leadbeater
    Participant

    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

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