All-Sky Imaging With the Fermi Gamma-ray Burst Monitor
Abstract
As demonstrated by BATSE and GBM, Earth occultation with non-imaging detectors can be used as a method for measuring source fluxes by looking at the differences in count rates in a detector that occur when a source moves into or out of occultation by the Earth. The Earth Occultation Technique applied to GBM's array of twelve NaI detectors makes it possible to monitor the entire sky every 26 days in the energy range 8 - 500 keV. The standard Earth Occultation Technique equires a predefined input catalog of source positions. Having an incomplete catalog has been shown to result in increased systematic errors. In order to find sources not included in the input catalog, an indirect imaging method has been developed that uses the projection of the Earth's limb onto the sky at the time a source occults. Over the course of an orbital precession period ( 53 days), all available projection angles are sampled. These projections add constructively near the position of a source, thus allowing the source to be localized. We present all-sky image results in the 12-25, 25-50, and 100-300 keV energy bands for 3 years of data from GBM, and discuss the correlations with the Swift/BAT, INTEGRAL/SPI, and Fermi/LAT catalogs.
- Publication:
-
AAS/High Energy Astrophysics Division #12
- Pub Date:
- September 2011
- Bibcode:
- 2011HEAD...12.2103R