# High-energy gamma-ray observations of Geminga with the Fermi Large Area Telescope

## TL;DR

This paper reports on Fermi LAT gamma-ray observations of Geminga, providing precise timing, spectral analysis, and insights into its energy-dependent light curve evolution over the first year of data.

## Contribution

It presents the first gamma-ray-only timing solution and detailed spectral evolution analysis of Geminga using Fermi LAT data.

## Key findings

- Precise gamma-ray timing solution for Geminga.
- Measurement of high-energy spectral cutoff.
- Analysis of spectral evolution with phase.

## Abstract

Geminga is the second brightest persistent source in the GeV gamma-ray sky. Discovered in 1975 by SAS-2 mission, it was identified as a pulsar only in the 90s, when ROSAT detected the 237 ms X-ray periodicity, that was later also found by EGRET in gamma rays. Even though Geminga has been one of the most intensively studied isolated neutron star during the last 30 years, its interest remains intact especially at gamma-ray energies, where instruments like the Large Area Telescope (LAT) aboard the Fermi mission will provide an unprecedented view of this pulsars. We will report on the preliminary results obtained on the analysis of the first year of observations. We have been able to do precise timing of Geminga using solely gamma rays, producing a timing solution and allowing a deep study of the evolution of the light curve with energy. We have also measured and studied the high-energy cutoff in the phase-averaged spectrum and produced a detailed study of the spectral evolution with phase.