Search for gamma-ray emission from magnetars with the Fermi Large Area Telescope

TL;DR

This study used Fermi-LAT data over 17 months to search for gamma-ray emission from magnetars, finding no significant signals and setting upper limits that challenge existing emission models.

Contribution

It provides the most stringent upper limits to date on gamma-ray emission from magnetars, informing and constraining theoretical models of their high-energy behavior.

Findings

No significant gamma-ray emission detected from magnetars.

Upper limits suggest a spectral cutoff below a few MeV.

Current models overpredict gamma-ray flux from magnetars.

Abstract

We report on the search for 0.1-10 GeV emission from magnetars in 17 months of Fermi Large Area Telescope (LAT) observations. No significant evidence for gamma-ray emission from any of the currently-known magnetars is found. The most stringent upper limits to date on their persistent emission in the Fermi-LAT energy range are estimated between ~10^{-12}-10^{-10} erg/s/cm2, depending on the source. We also searched for gamma-ray pulsations and possible outbursts, also with no significant detection. The upper limits derived support the presence of a cut-off at an energy below a few MeV in the persistent emission of magnetars. They also show the likely need for a revision of current models of outer gap emission from strongly magnetized pulsars, which, in some realizations, predict detectable GeV emission from magnetars at flux levels exceeding the upper limits identified here using the Fermi-LAT observations.