Simulations of the Gamma-Ray Sky

The Gamma-Ray Large Area Space Telescope (GLAST) will observe the sky in gamma-rays with energies between 10 million electron volts (MeV) to 300 billion electron volts (GeV) (a photon of visible light is roughly 2 electron volts). At these energies, the detectors will receive roughly 2 photons every second. At these energies, the objects visible will be active galaxies, quasars, pulsars, and gamma-ray bursts. This visualization is generated from one year of simulated photon event-lists using known sources. These event lists are used for testing the various data analysis software being developed for the project. Due to the extremely low event rate, it takes about one week of event accumulation to see structure in the sky. To generate the 600+ frames of this visualization, the event lists were box-car averaged for a duration of one week for each frame, and each frame shifted 50,000 seconds in time from the previous frame. The low angular resolution of gamma-ray detectors makes point sources appear spread out in the sky. In these maps, the color of each pixel represents the number of photons accumulated in that pixel (over an energy range of 10MeV-300GeV). Horizontally, across the center of the map, is the diffuse emission from the plane of our own Milky Way galaxy. The images are projected in galactic coordinates with a plate carrée projection so there is significant distortion with increasing latitude above the galactic disk. This emission in the galactic plane is created by pulsars and supernova remnants. Located away from this plane is emission from active galaxies and high-velocity pulsars. Occasionally, a bright spot appears which can be a gamma-ray burst or quasar in an active state.