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Fig. 3

image

Upper panel: hits image obtained by counting the raw detections within each pixel (cf. Sect. 3), zoomed in on the bulge. The blue cross marks the center of M 31 and the red ellipses show the location of sources found by WAVDETECT in this region. North is upward and east is left. As the area around the center is masked upstream in the iPTF pipeline due to saturation, the corresponding pixels in the hits image have zero values. The stripe that can be seen left of the center arises from the border between blocks used to match the background in the iPTF DI pipeline (cf. Fig. 1). Lower panel: outer part of the hits image, half a degree northward of the M 31 center, with the red ellipses showing the location of sources found by WAVDETECT. The shape of the elliptical region characterizes the shape of the distribution of counts within the source cell. Some of these regions output by WAVDETECT may have a very small length along one of the axes, such that they appear as lines; these regions are however only meant for visualization (see text).

This figure is made of several images, please see below:

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