Simultaneous X-Ray, Gamma-Ray, and Radio Observations of the Repeating Fast Radio Burst FRB 121102

We undertook coordinated campaigns with the Green Bank, Effelsberg, andArecibo radio telescopes during Chandra X-ray Observatory and XMM-Newtonobservations of the repeating fast radio burst FRB 121102 to search forsimultaneous radio and X-ray bursts. We find 12 radio bursts from FRB121102 during 70 ks total of X-ray observations. We detect no X-rayphotons at the times of radio bursts from FRB 121102 and further detectno X-ray bursts above the measured background at any time. We place a5σ upper limit of 3 × 10‑11 ergcm‑2 on the 0.5–10 keV fluence for X-ray burstsat the time of radio bursts for durations <700 ms, which correspondsto a burst energy of 4 × 1045 erg at the measureddistance of FRB 121102. We also place limits on the 0.5–10 keVfluence of 5 × 10‑10 and 1 ×10‑9 erg cm‑2 for bursts emitted atany time during the XMM-Newton and Chandra observations, respectively,assuming a typical X-ray burst duration of 5 ms. We analyze data fromthe Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor and place a5σ upper limit on the 10–100 keV fluence of 4 ×10‑9 erg cm‑2 (5 ×1047 erg at the distance of FRB 121102) for gamma-ray burstsat the time of radio bursts. We also present a deep search for apersistent X-ray source using all of the X-ray observations taken todate and place a 5σ upper limit on the 0.5–10 keV flux of 4× 10‑15 erg s‑1cm‑2 (3 × 1041 ergs‑1 at the distance of FRB 121102). We discuss thesenon-detections in the context of the host environment of FRB 121102 andof possible sources of fast radio bursts in general.