I am not an astrophysicist but seems to me that the radiation from a supernova should arrive some time after the light produced from the supernova. Things with mass like protons and neutron travel slightly slower than the speed of light
So attributing the C-14 in tree rings of the same year in Japan seems a stretch.
Also should there not be extra C-14 world wide from such an event.
The radiation from a super nova should strike the entire planet or at least the extra C-14 created in the upper atmosphere should be fairly evenly distributed as is disperses to lower altitudes.
There might be, but others elsewhere may not have looked specifically at that time frame.
Carbon-14, a radioactive version of a carbon atom with six protons and eight neutrons, forms when gamma rays from space strip atmospheric atoms of their neutrons, which then collide with the isotope nitrogen-14 and cause it to radioactively decay into carbon-14.
I'm not a scientist either, but any thinking person would also think C-14 would be everywhere, not just in Japan's cedar trees.
Besides, I thought C-14 had a constant decay rate and now they are saying it can be added after every stellar event? That would seem to change numbers everywhere and skew all kinds of numbers.
We KNOW the dates of some events because it is in recorded history. If we have stellar events between then and now, it looks like we could Measure C-14 from that period to check to see if there was a date skew in the measurements.
I think someone is looking for grant money instead of a job.
The C-14 was not propelled directly from the supernova, but was formed here when the wave of radiation from the supernova passed through. If memory serves, gamma will cause a lot more of that isotope to form all at one time, resulting in a weird “spike.”
I highly recommend the book that SunkenCiv has linked to. Forestone explains a great deal in it about the processes involved in supernova effects and Earth.