The multichromatic wavelet transformation as a source identification tool for GLAST

Abstract

The GLAST mission (Gamma-ray Large Area Space Telescope) will yield a great amount of photon data in the region from 30 MeV to 300 GeV. However, the sparsity of incoming photon events and strong dependence of instrument response on photon energy necessitate data analysis techniques different from those used in similar areas such as X-Ray astronomy. A modified form of the continuous wavelet transformation (CWT) has been developed for use in finding point sources from sparse photon data. This method has multiple advantages over other source location strategies, and is developed as a source finding algorithm. As the efficiency of this method is well characterized, this method is also useful in estimation of the total contribution of unresolvable sources to the observed extragalactic gamma-ray intensity. Using this method, we are able to estimate the ratio of the extragalactic gamma-ray background accounted for by diffuse emission of photons. With foreknowledge of the instrument response of GLAST, and the point-source resolution algorithm to be used, an estimate can be made of the diffuse component necessary to be significantly measured in this way. This "diffuse discrimination threshold" has been measured for GLAST, at the level of a few percent. The Point Soure Sensitivity (PSS) of GLAST has also been estimated to be about 6.3 · 10 -9 cm-2s-1.