Comparison of WGACAT with ROSATSRC

Nick White, NASA/Goddard Space Flight Center-HEASARC

Paolo Giommi , ESA/ESRIN-ESIS

Lorella Angelini, NASA/Goddard Space Flight Center-HEASARC

The results of the source detect run as part of the Rev 0/1 SAS processing have recently been made available as the BROWSE database ROSATSRC. This contains about 50,000 detections, with 45,000 individual sources. These numbers are similar to those found in WGACAT. However, a closer inspection of the two catalogs reveals major differences. Taking just the inner 20 arc min region we find that ROSATSRC has roughly twice as many sources as WGACAT. This results because the SAS detect uses a lower threshold. In WGACAT these sources would not pass the probabilty test of being less than 1.0E-4 due to random fluctuations, with a SNR greater than 2.0. In the outer region WGACAT contains twice as many detections as does ROSATSRC. This seems to result from a change to a more conservative detect threshold. This difference is well illustrated by comparing the count rate vs. off axis angle for the two catalogs (Figure 1).

Count rate versus offaxis angle for WGACAT Count rate versus offaxis angle for the SAS catalog

Figure 1. The WGACAT source count rate (left/top) as a function of its off axis angle (in arc minutes) and the same plot for the SAS Rev0/1 catalog (right/bottom).