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many concentric sets of sheets, which all
together can collect most of the X-ray pho-
tons that enter the telescope. In NICER
specifically, the XRCs in the XTI consist of
24 concentric truncated cones, on which the
X-ray photons complete a single bounce
because, unlike previous instruments, XTI
does not have to produce images and thus
does not require a tight focus.
Having ended our digression, we return to
the XTI’s ability to measure with great pre-
cision the energy of the captured photons
and their times of arrival on the detector.
Knowing the exact energy of the X-ray
photons means getting spectrometric val-
ues that can provide important informa-
tion about the sources that emitted them.
Knowing the exact arrival time for the X-
ray photons, on the other hand, means
being able to place each event with preci-
sion on the source’s light curve, accumu-
lating them over days and months of ob-
servation, provided they follow a regular,
periodic progression, as happens with the
targets chosen for NICER, which are pul-
sars without increases in mass from com-
panion stars (a phenomenon that would
contaminate their light curves, making
analysis even more complicated). Now, how
can NICER be so precise in observing ob-
G
raphic repre-
sentation of
the NICER pay-
load aboard the
International
Space Station.
[NASA]