A Search for the Guest Star Associated with Swift J1818.0-1607

Recently found magnetar Swift J1818.0-1607, with the characteristic age $\tau_c=P/(2\dot{P})\simeq240$ yr in the Milky Way, is the youngest magnetar discovered to date. With an estimated age of 240 yr, we searched ancient Chinese records during the eighteenth century. We found a guest star in AD 1798 that might be associated with it.