  Given that the cause for the strong increase in 14C in AD 774/5 in Japanese
and German trees is still a matter of debate (e.g. short Gamma-Ray Burst or
solar super-flare), we have searched in Arabic chronicles for reports about
unusual transient celestial events. In the History of al-Tabari we found two
(almost identical) reports about such an event. The group around caliph
al-Mansur observed a transient event while on the way from Baghdad to Mecca on
AD 775 Aug 29 - Sep 1 (Julian calendar). A celestial object (kawkab) was seen
to fall or set (inqadda), and its trace (atharuhu) was seen for at least tens
of minutes (up to 70-90 min) during morning twilight. The reports use the
Arabic words kawkab and athar(uhu), which were also used in the known Arabic
reports about supernovae SN 1006 and 1054, so that one might consider an
interpretation as a nova-like event. The kawkab (celestial object) was observed
only during the morning twilight at a brightness of probably between about -3
and 0 mag. Such a brightness and time-scale would be expected for optical
kilonovae (at 3 to 9 kpc) in the context of short Gamma-Ray Bursts. There are
no similar reports from eastern Asia for this time. However, the short reports
are fully consistent with a bolide: The word kawkab can be used for meteor, the
verb inqadda normally means "falling down", the word atharuhu can mean "its
trace". We therefore prefer the interpretation as bolide. We discuss in detail
how to convert the Muslim calendar date to a date in the Julian calendar using
first the calculated Islamic calendar and then considering the time when the
crescent new moon could be visible at the given location.
