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We have identified as our highest priority sources those which meet the following four criteria:
These criteria were chosen in order to ensure that a well defined,
flux-limited sample can be achieved. Over 200 candidate blazars met the
above defining criteria (details are given below).
In addition, 98 previously identified but serendipitously observed
objects meet our criteria (see § 4.3). Lower-galactic-latitude and
lower-flux sources were assigned to a lower-priority list, but are
useful in order to fill in higher LX/LR areas of parameter space.
No pre-selection was imposed on WGACAT in the region , although for ease of identification we avoided the regions
within
of the Large and Small Magellanic Clouds, as well as M31.
Note that although we have not imposed
any cut in X-ray flux, our sample will have both radio and X-ray flux limits,
the latter depending on the region of the sky surveyed due to the serendipitous
nature of WGACAT (similarly to the EMSS). Depending on the length of each
individual exposure and the distance from the center of the PSPC field,
the X-ray flux limits appropriate for each source will vary between
and
erg cm-2 s-1.
The slightly different radio flux limits north and south of the equator
are simply explained: For
(and
, the
limit of the GB6 catalog), it is easy to see that all sources with
mJy (the limit of the NORTH20CM catalog) and
will be above the much lower flux limit of the GB6
catalog (
mJy; note that the converse does not hold).
For
, on the other hand, our radio flux limit is the
completeness
limit of the PMN survey, which (while declination dependent; see
Griffith & Wright 1993) averages about 50 mJy.