Evidence for GeV Emission from the Superluminous Supernova SN 2017egm

Superluminous supernovae (SLSNe) are a new class of transients with luminosities ∼10-100 times larger than the usual core-collapse supernovae. Their origin is still unclear. One widely discussed scenario involves a millisecond magnetar central engine. The GeV-TeV emission of SLSNe has been predicted in the literature but has not been convincingly detected yet. Here, we report the results of the search for γ-ray emission in the direction of SN 2017egm, one of the closest SLSNe detected so far, using 15 years of Fermi-LAT Pass 8 data. There is a transient γ-ray source appearing about two months after this event and lasting a few months. Monte Carlo simulations show that the γ-ray signal has a global significance of at least 4σ. Both the peak time and the luminosity of the GeV emission are consistent with the magnetar model prediction, suggesting that such a GeV transient is the high-energy counterpart of SN 2017egm and the central engine of this SLSNe is a young magnetar.