Yes, this 774-775AD event has been discussed a little by some of us. I believe that this event may have caused a 10C rise in temperature _in one year_, according to Antarctic core data. Or perhaps our "thermometer", which itself depends upon isotope data, was majorly upset by an xray blast. Even if only 2 seconds long, such a blast would certainly have been noticed by human beings. It might be interesting to try to figure out what part of the Earth was exposed; perhaps that area was thinly populated. While this particular burst seems to have hit the Earth itself, who knows what effects bursts of this type might have on the Sun & its output at other times when the Earth might not have been directly hit. The differential isotope studies are relatively new (< 50 years?) with machines of the precision to detect isotope differences in whole molecules only now coming on-line (e.g., at Caltech), and therefore enormous amounts of data gathering are left to be done. I don't know if any of the NASA probes are capable of such techniques, but we have a huge amount to learn about the relative isotope ratios in different parts of the solar system. For example, it would be interesting to know if such an xray blast hit the Moon, Mars, etc., at the same time. I've heard it said that differential isotope techniques might be useful in determining where (radius from the Sun) and when a planet was formed, so that theories of planet formation & subsequent movement to present orbits can be solidified. At 03:01 PM 1/22/2013, Warren Smith wrote:

This paper

V. V. Hambaryan, R. Neuhaeuser: A Galactic short gamma-ray burst as cause for the 14C peak in AD 774/5 http://arxiv.org/abs/1211.2584

claims in 1 year either 774 or 775 AD, the concentration of carbon 14 increased by an amount equivalent to 14C production in 10 typical years. As detected in tree rings on 2 continents. Also there was a spike in 10Be at the same time (to within time measurement errors). This was the only such spike during the last 3K years.

They explain this by postulating there was a gamma ray burst which fried the Earth for 2 seconds with 7*10^17 joules of gamma ray energy. (This is equivalent to the energy of the sunlight hitting the Earth during 4 seconds, but in gamma ray rather than light region of spectrum.) This was presumably caused by e.g. merger of 2 neutron stars at a distance of 3K to 13K lightyears. They think if it had been much closer than that it would have caused notable extinction (of life) events... over, I presume, exactly half of the Earth(?)... which did not happen.

I have a problem with this. If you believe them and believe such events happen at least once every 5000 years within 3K to 13K lightyears distance, then it would follow they ought to happen within 1K lightyears at least once every 11M years. Causing big fat extinction events over exactly half the Earth, at that frequency. Which haven't been noticed (have they)?