…there is another magenta point nearby, which I used for comparison. But this looks rather unspectacular to me, because firstly only really appears in the z-band (a little in the r) and is also visible on all images in the z-band.
So I think the magenta point mentioned above might be something special.
This looks to be a supernova, visible in exposures ranging from 2017-08-03 to 2017-10-15. Couldn’t be found on TNS or BSP so it looks like you found a new one.
Edit: It kind-of-is in the legacy Surveys DR9 catalog but the marked area is a bit off - and the given magnitude looks a bit too high (magnitudes have a negative scale) so unfortunately I’m unable to report this.
I think it is an unreported #supernova candidate. I want to report but first I have to report two other supenova candidates. And I have to calculate an Apparent magnitude because there is no given magnitude in one of the DECaLS catalogs. To report I need your real name. TNS does not accept nicknames. But if you don’t want this I can put your nickname in the comments section. So it is up to you.
Oh, I would of course be very happy, Ine. I wrote you a short private message about this and would be very happy if I would be named there as a finder.
P.S. Unfortunately, I couldn’t be online here for the entire last week, but at the weekend I’ll go straight back to looking for new interesting things.