Image Details
Caption: Figure 1.
Effective area (red line) of the NICER XTI concentrator optics as a function of photon energy, derived from ray-tracing simulations and neglecting low-energy absorption from filters in the optical path; also shown is the estimated effective area (blue line) at 1.′5 off axis, appropriate for the NICER observations of PSR J0437−4715 (see the Appendix for details). The reduction in sensitivity of the off-axis response has weak or no energy dependence, as shown by the ratio of the off- and on-axis spectrum ratio (black line) measured via observations of the Crab Nebula and pulsar; variations from channel to channel are due to statistical fluctuations.
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