Fermi Large Area Telescope Gamma-Ray Detection of the Radio Galaxy M87

We report the Fermi LargeArea Telescope (LAT) discovery of high-energy (MeV/GeV) γ -ray emission positionally consistent with the center of the radio galaxy M87, at a source significance of over 10σ in 10 months of all-sky survey data. Following the detections of Cen A and Per A, this makesM87 the third radio galaxy seen with the LAT. The faint point-like γ -ray source has a >100 MeV flux of 2.45 (±0.63) × 10−8 photons cm−2 s−1 (photon index = 2.26 ± 0.13) with no significant variability detected within the LAT observation. This flux is comparable with the previous EGRET upper limit (<2.18×10−8 photons cm−2 s−1, 2σ), thus there is no evidence for a significant MeV/ GeV flare on decade timescales.Contemporaneous Chandra andVery Long BaselineArray data indicate lowactivity in the unresolvedX-ray and radio core relative to previous observations, suggesting M87 is in a quiescent overall level over the first year of Fermi-LAT observations. The LAT γ -ray spectrum is modeled as synchrotron self-Compton (SSC) emission from the electron population producing the radio-to-X-ray emission in the core. The resultant SSC spectrum extrapolates smoothly from the LAT band to the historical-minimum TeV emission. Alternative models for the core and possible contributions from the kiloparsec-scale jet in M87 are considered, and cannot be excluded.