I was inspecting the infrastructure points I have on my Google Cloud to remove any lose points...

Then i noticed that google cloud storage have 5 buckets [even that i just created 2 of them]  

these 5 buckets are:
1 - bucket i created  

2 - bucket i created  

3 - PROJECT.backups  

4 - gcf-sources-CODE-us-central1  

5 - us.artifacts.PROJECT.appspot.com

I understand that the backups bucket come from firebase realtime database backups and the sources bucket come from the firebase cloud functions code. BUT where does the artifacts bucket comes from? this bucket alone has TWICE the size of all other buckets together.

Its contents are just binary files named like "sha256:HASH" some of which are larger than 200MB

I deleted this bucket and it was re-created [without my interaction] again next day.

Does anyone know what might be using it? how can i track it down? what is it for?