# Unbinned Likelihood Analysis of EGRET Observations

### S. W. Digel

## Abstract

We present a newly-developed likelihood analysis method for EGRET data
that defines the likelihood function without binning the photon data or
averaging the instrumental response functions. The standard likelihood
analysis applied to EGRET data requires the photons to be binned
spatially and in energy, and the point-spread functions to be averaged
over energy and inclination angle. The full-width half maximum of the
point-spread function increases by about 40% from on-axis to
30\arcdeg inclination, and depending on the binning in energy can vary by
more than that across a single energy bin. The new unbinned method avoids
the loss of information that binning and averaging cause and can
properly analyze regions where EGRET viewing periods overlap and photons
with different inclination angles would otherwise be combined in the
same bin. In the poster, we describe the unbinned analysis method and
compare its sensitivity with binned analysis for detecting point sources
in EGRET data.

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On 16 Jul 1999, 09:19.