Repeating FRB 121102 : Eight-year Fermi-LAT Upper Limits and Implications

Abstract

The repeating fast radio burst (FRB) source that produced FRB 121102 was recently localized in a star forming galaxy at $z=0.193$, which is associated with an extended radio source at the burst location. One possibility is that the repeating FRBs are produced by a new-born magnetar, which also powers the radio nebula. If so, the magnetar may produce ${\hat{I}}^3$-ray emission due to magnetic dipolar spin-down. The luminosity depends on the magnetar spin parameters and age. We process the eight-year Fermi LAT data at the position of FRB 121102 and place an energy flux upper limit of $\sim 10^{-11}\mathrm{erg}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ in time bins with six-month intervals, and an accumulated energy flux upper limit of $\sim 4\times 10^{-12}\mathrm{erg}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ over the eight year span. The corresponding ${\hat{I}}^3$-ray luminosity upper limits are $\sim 10^{45}\mathrm{erg}{\mathrm{s}}^{-1}$ and $\sim 4\times 10^{44}\mathrm{erg}{\mathrm{s}}^{-1}$ for the time-resolved and time-integrated analyses, respectively. We discuss the implications of these limits on the young magnetar model.

4 pages, 3 figures, ApJL in press