SkyView Fermi LAT Surveys

We have just released two gamma-ray all-sky surveys based upon the Fermi LAT weekly data. Fermi images go much deeper and have somewhat higher resolution than the old EGRET surveys. Fermi is also sensitive to gamma-rays at significantly higher energies, up to 300 GeV.

The two surveys cover the bands 0.1-5.4 GeV and 5.4-300 GeV. There are many more counts in the lower energy survey and many more sources are apparent there. The surveys are generated from the weekly exposure maps and photon lists supplied by the Fermi LAT team. The exposures are summed together to create an overall exposure map and the photon lists are combined and resampled in 1/8 degree pixels in a Cartesian projection. The combined exposure at the center of each of these pixels is then sampled and weighted by the size of the pixel to get the normalized exposure. The ratio of the counts to the weighted is used to get the intensity of the pixel. Currently we are only providing the intensity maps but we can also include the counts and exposure maps if there is interest. We also hope to provide a 3-D Fermi survey with perhaps 10 energy bands.

Fermi’s new hard band extends SkyView‘s frequency coverage a full decade above the previous upper limit.

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