  The nature of fast radio bursts (FRBs) is currently unknown. Repeating FRBs
offer better opportunity than non-repeating FRBs since their simultaneous
multi-wavelength counterparts might be identified. The magnetar flare model of
FRBs is one of the most promising models which predicts high energy emission in
addition to radio burst emission. To investigate such a possibility, we have
searched for simultaneous and quasi-simultaneous short-term hard X-ray bursts
in all the Swift/BAT event mode data which covered the periods when fast radio
bursts were reported detections in the repeating FRB 121102, by making use of
BAT's arcmin level spacial resolution and wide field-of-view. We did not find
any significant hard X-ray bursts which occurred simultaneously to those radio
bursts. We also investigated potential short X-ray bursts occurred
quasi-simultaneous with those radio bursts (occurrence time differs in the
range from hundreds of seconds to thousands of seconds) and concluded that even
the best candidates are consistent with background fluctuations. Therefore our
investigation concluded that there were no hard X-ray bursts detectable with
Swift/BAT which occurred simultaneously or quasi-simultaneously with those fast
radio bursts in the repeating FRB 121102.
