---
author:
- 'R. Neuhäuser [^1]'
- 'P. Kunitzsch'
title: 'A transient event in AD 775 reported by al-abar$\bar{\i}$: A bolide - not a nova, supernova, or kilonova'
---

*Introduction: $^{14}$C variation in AD 774/5*
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Miyake et al. (2012) detected a significant variation in the isotope ratio of $^{14}$C to $^{12}$C in two Japanese trees around AD 774, which was confirmed by Usoskin et al. (2013) with a German tree. Depending on the carbon cycle model, the energy estimate would be either $7 \times 10^{24}$ erg in $\gamma$- and/or cosmic rays at Earth within one year, if the radioisotopes were formed due to incoming $\gamma$-photons above 10 MeV with a supernova-like spectrum with a power-law index of $-2.5$ (Miyake et al. 2012), or 4 to 6 times less using a different carbon cycle model (Usoskin et al. 2013).

Since there was significantly ($7.2~\sigma$) more $^{14}$C detected in the AD 775 trees than in AD 774, the event should have taken place in AD 774. However, there may be some uncertainties in the exact dating: (i) Some trees may not form any rings at all in very cold years (e.g. Mann et al. 2012); (ii) some trees may be able 