PhD Thesis (PDF) - Department of Astronomy - University of Virginia

source list against which to register the astrometry. We detected 97, 78, 87, 77, and
98 sources in Observations 0784, 4727, 4728, 4729, and 4730. We then registered the
astrometry of each Cycle-5 observation against Observation 0784. Using 55, 56, 51,
and 55 sources matched to within 0. ′′ 5, the relative astrometry corrections were 0. ′′ 31,
0. ′′ 38, 0. ′′ 31, and 0. ′′ 48.
To maximize S/N, we analyzed the wavelet detection results from the combination
of the five observations (Figure 5.1). Since there were five approximately equally sen-
sitive observations, we reduced the exposure threshold of this merged source detection
to 2% of the total. There was a 50% increase in the FOV compared to a single S3
chip, so we expect 1.5 false source. We detected 158 sources. All of the detections
in Observation 0784 were in the merged detection list. In the Cycle-5 observations,
a few weak detections were not found in the merged detection list. None of these de-
tections would have fluxes determined at the ≥ 3σ level; detections not in the merged
detection list are not discussed further in this chapter.
We used the coordinate list generated by wavdetect in ACIS Extract to create
source extraction and masking regions, as well as refine the source positions. For
each observation, we created a source extraction region consistent with the X-ray
PSF at the source position. Most of the regions encircled 90% of the X-ray PSF at
≈ 1.5 keV. For sources whose median photon energy over all five observations was
not ∼ 0.6–2.6 keV, we determined the PSF at either ≈ 0.3 keV (Sources 19, 23, 25,
62, and 78) or ≈ 4.5 keV (Sources 96, 119, and 138). We used a lower percentage of
the PSF in the case of few sources whose regions would otherwise have overlapped in
one of the observations (85% for Sources 2/5; 80% for Sources 49/50; 50% for Sources
72/73). The wavdetect regions were compared to the PSF sizes at the locations of
the sources; all were consistent except those for Sources 8, 22, 123, and 158. Thus,
149