At this point, it should be possible to simply add up the number of counts in a range of annuli around the source and divide by the total effective area in the same annulus to get the surface brightness as a function of radius R from the source. However, examining the image shows that there's a problem - there is a 'jet' of emission coming out at around 10 o'clock. This is a bit easier to see in the 'zoomed' image, but it's definitely there. The first time I saw this, I thought I'd actually found a jet of X-ray emission coming from the neutron star, something that could happen. However, in this case it turns out it's a well-known problem with the HRC that 'misaligns' a few counts (less than a percent or so) in a particular direction. This is
normally filtered away, but in high count rate situations like this the filter doesn't work perfectly. The only way to realistically deal with this is to simply exclude that side of the source from the final result. This doesn't guarantee it won't impact the final result slightly, but it's the best I can do. Fortunately, the side I'm excluding is facing the edge of the detector so it's a relatively small area and, secondly, there are beaucoup counts in this dataset in the first place, so the impact is limited.
At this point, it should be possible to simply add up the number of counts in a range of annuli around the source and divide by the total effective area in the same annulus to get the surface brightness as a function of radius R from the source. However, examining the image shows that there's a problem - there is a 'jet' of emission coming out at around 10 o'clock. This is a bit easier to see in the 'zoomed' image, but it's definitely there. The first time I saw this, I thought I'd actually found a jet of X-ray emission coming from the neutron star, something that could happen. However, in this case it turns out it's a well-known problem with the HRC that 'misaligns' a few counts (less than a percent or so) in a particular direction. This is normally filtered away, but in high count rate situations like this the filter doesn't work perfectly. The only way to realistically deal with this is to simply exclude that side of the source from the final result. This doesn't guarantee it won't impact the final result slightly, but it's the best I can do. Fortunately, the side I'm excluding is facing the edge of the detector so it's a relatively small area and, secondly, there are beaucoup counts in this dataset in the first place, so the impact is limited.
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