A Search for Hard X-Ray Bursts Occurring Simultaneously with Fast Radio Bursts in the Repeating FRB 121102

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.