Fermi-LAT Detection of Pulsed Gamma-rays Above 50 GeV from the Vela Pulsar

TL;DR

This paper reports the first significant detection of pulsed gamma-ray emission above 50 GeV from the Vela pulsar using 62 months of Fermi-LAT data, confirming very high-energy pulsation with high statistical significance.

Contribution

It provides the first robust evidence of pulsed gamma-ray emission from Vela above 50 GeV, extending the known energy range of pulsar gamma-ray emission and exploring the outer gap emission scenario.

Findings

Pulsation detected above 50 GeV with 4.2σ significance.

Significant pulsation observed above 79 GeV and 90 GeV energy bands.

Analysis confirms the highest energy pulsation detected by Fermi-LAT.

Abstract

The First \fermi-LAT Catalog of Sources Above 10 GeV reported evidence of pulsed emission above 25 GeV from 12 pulsars, including the Vela pulsar, which showed evidence of pulsation at $>37$ GeV energy bands. Using 62 months of \fermi-LAT data, we analyzed the gamma-ray emission from the Vela pulsar and searched for pulsed emission above 50 GeV. Having confirmed the significance of the pulsation in 30-50 GeV with the H-test (p-value $\sim10^{-77}$), we extracted its pulse profile using the Bayesian block algorithm and compared it with the distribution of the 5 observed photons above 50 GeV using the likelihood ratio test. Pulsation was significantly detected for photons above 50 GeV with p-value $=3\times10^{-5}$ ($4.2\sigma$). The detection of pulsation is significant above $4\sigma$ at $>79$ GeV and above $3\sigma$ at $>90$ GeV energy bands, making this the highest energy pulsation significantly detected by the LAT. We explore non-stationary outer gap scenario of the very high-energy emissions from the Vela pulsar.