possible supernova AT 2021gmj in NGC3310 (UMa)

[Robin Leadbeater]

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

Discovered today at mag 16 but at only ~11Mpc could potentially get much brighter in the coming days depending on type (A type Ia could reach ~mag 11 in the absence of extinction)
Well placed (It is almost exactly at the zenith at 23:00 for me)

Robin

[David Swan]

Captured at 20:32 UT this evening (20 Mar).

[David Swan]

Astrometrica puts it ~ mag 15.6

[Robin Leadbeater]

Now classified as a type II. Not surprising for a star burst galaxy I guess

https://www.wis-tns.org/astronotes/astronote/2021-93

[Maxim Usatov]

I have it at V = 15.77 ± 0.05, although correct PSF fit is a little difficult.

Observatory:  New Mexico Skies at Mayhill, New Mexico – MPC H06
Telescope:  0.50-m f/6.8 reflector + CCD + f/4.5 focal reducer
CCD:  FLI ProLine PL11002M CCD camera

Filter is Astrodon V.

[Robin Leadbeater]

The spectrum at maximum (15.8 ZTF g) showing nice broad Hydrogen Balmer line P Cygni profiles 

[Hugh Allen]

Hi Robin,

Very nice supernova spectrum as always. What is the correct way to estimate ejecta velocities along the line of sight from P Cygni profiles? Is it the emission centre to the absorption minimum or to the absorption blue edge?

Cheers

Hugh

[Robin Leadbeater]

I normally just measure the shift of the absorption minimum, either relative to the line rest wavelength corrected for z if known or the emission maximum. I guess there must be higher velocities out to the edge of the line where it meets the continuum but my resolution is so low it would bias the result. It looks like the 13500km/s measured in the very early classification spectrum was based on where the broad H alpha emission met  the continuum.

[Maxim Usatov]

V = 15.778 ± 0.07 with slightly better data from tonight.

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

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