OPPORTUNITY FOR EGRET DATA ENHANCEMENT

[Chris Shrader <shrader@grossc.gsfc.nasa.gov>]

18 Aug. 1998

OPPORTUNITY FOR EGRET DATA ENHANCEMENT

As part of a CGRO Cycle7 proposal, the EGRET team has reprocessed
several
blocks of EGRET events from times when the EGRET spark chamber
performance was weak, primarily in the later observation cycles.  This
reprocessing is labor-intensive, since it involves looking for
acceptable gamma rays among the many events that were originally
rejected by the processing system.  Nevertheless, we have found that
such reprocessing typically increases the statistics for invidivual
sources by 25 to 50%, allowing some additional scientific return.  The
absolute calibration of such reprocessed data is uncertain. The use of
events that were originally rejected necessarily introduces some
background that was not present in the original data. The primary
utility  of this reprocessing is two-fold:
1. Increase statistics for observations when sources were time-variable.

2. Enhance the significance of otherwise-marginal detections.

Thus far, the observations that have been re-analyzed are:
VP 423.5  PKS 1622-297 flare   (work still in progress)
VP 511, 511.5   3C279 flare
VP 528    Galactic anticenter
VP 623.5  BL Lac flare

A CGRO Cycle 8 proposal has been accepted to continue this work and to
place the
reprocessed data sets into a special location in the CGRO archive

With this note, we solicit comments and suggestions
about which viewing periods to re-analyze.  Subject to such comments,
our intention is to focus on observations of AGN showing variability or
those with marginal detections, such as the Mkn 501 viewings.

Please send comments to Dave Thompson, djt@egret.gsfc.nasa.gov.