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

## TL;DR

This study uses eight years of Fermi-LAT data to set upper limits on gamma-ray emission from the repeating FRB 121102, constraining models involving young magnetars as the source.

## Contribution

It provides the first long-term gamma-ray flux upper limits for FRB 121102, informing magnetar-based models of repeating fast radio bursts.

## Key findings

- Gamma-ray luminosity upper limits of ~10^{45} erg/s for time-resolved data.
- Gamma-ray luminosity upper limits of ~4×10^{44} erg/s for the entire data span.
- Constraints on young magnetar models based on gamma-ray emission limits.

## 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 $\gamma$-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 $\sim 10^{-11} \ {\rm erg \ cm^{-2} \ s^{-1}}$ in time bins with six-month intervals, and an accumulated energy flux upper limit of $\sim 4\times 10^{-12} \ {\rm erg \ cm^{-2} \ s^{-1}}$ over the eight year span. The corresponding $\gamma$-ray luminosity upper limits are $\sim 10^{45} \ {\rm erg \ s^{-1}}$ and $\sim 4\times 10^{44} \ {\rm erg \ s^{-1}}$ for the time-resolved and time-integrated analyses, respectively. We discuss the implications of these limits on the young magnetar model.