Evidence for 500 TeV gamma-ray emission from Hercules X-1

Abstract

A signal (chance probability = 2×10<SUP>-4</SUP>) with a 1.24 s period has been observed from the direction of Hercules X-1. The signal's relatively long period and high shower energy conflict with some popular models of particle acceleration by pulsars. Optical and X-ray data support a picture in which energetic particles produce multi-TeV γ-rays by collisions with Hercules X-1's accretion disk.