StarTools

I happened to have been imaging M101 on the nights of May 9, 16 and 17 (thanks to the CN monthly beginner's target). I was able to image it again on the night of May 20. The images below were captured with an AT130EDT f/7 refractor + 0.8x reducer and Risincam IMX571c camera on a CEM40 mount guided with an OAG + QHY5iii462C camera. The pre-SN image on the left comprises 258 x 120s exposures, the with-supernova image on the right is 166 x 120s (the May 20 image suffers from the wildfire smoke). Both images pre-processed and stacked in Siril and post-processed in StarTools 1.9 alpha.

I don't normally crop this close, but this seemed the right approach here. Also - this should be my last image with weird circular impossible-to-fully-correct gradients, as I finally located and squashed my light leak (it was from the underside of the guide camera platform on the Orion TOAG). My flats look like proper flats again, finally.

Another great before-and-after of the SN!
Good to hear you got that light leak dealt with. If all that you got left are gradients, then you will be able to go much deeper, and you will get signal/detail you can trust. Processing will become much easier too.