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J. G. Stacy (LSU & SU), S. C. Kappadath (LSU), W. Collmar, V. Schönfelder, H. Steinle, A. W. Strong (MPE), H. Bloemen, W. Hersmen (SRON-Utrecht), J. M. Ryan (UNH), O. R. Williams (ESA/ESTEC)
We have extended our earlier work to establish cumulative flux limits in the COMPTEL energy range (0.75-30 MeV) for a large sample of active galactic nuclei (AGN) of general interest. The target list of objects consists of known or suspected gamma-ray sources at high Galactic latitude, including unidentified sources listed in the Third EGRET Catalog of Hartmann et al. (1999, ApJS, 123, 79). Limits to the time-averaged MeV-emission measured with COMPTEL are derived from all-sky maximum-likelihood significance and flux maps produced using COMPTEL datasets spanning the time period April 1991 to November 1997 (i.e., through CGRO Cycle 6). We describe our data-processing and analysis procedures and present a summary of the results obtained. These latest limits are compared to our original results presented in the First COMPTEL Source Catalog of Schönfelder et al. (2000, A&ASupplSer, 143, 145) for which we employed composite all-sky maps covering a more restricted time period of observation. The latest flux limits obtained here will be used to assess the possible contribution of AGN to the diffuse gamma-ray background measured with COMPTEL in the MeV regime.
This research and the CGRO/COMPTEL project have been supported by NASA, the German government through DARA, and the Netherlands Organisation for Space Research (NWO).