X-RAY TELESCOPES MEASURE: COUNTS/(INTEGRATED TIME BIN)/”CHANNEL”
COUNTS ARE NOT PHOTONS! POISSON STATISTICS ARE COMMONLY USED CHANNELS ARE NOT ENERGY!
In short:
ARF = Telescope Area × Filter Throughput × Detector Efficiency × Other Factors
Each component affects the effective area differently:
| Component | Effect |
|---|---|
| Mirrors | Reflectivity depends on energy and angle of incidence; on-axis photons hit mirrors head-on, off-axis photons hit at grazing angles → lower reflectivity. |
| Collimators | Restrict field of view; block off-axis photons more effectively. |
| Filters | Absorb certain energies; e.g., UV blocking filters or calibration materials. |
| Detectors | Quantum efficiency varies with energy; some detectors are better for low or high energy photons. |
These combine into a structured ARF , which may have peaks, dips, and edges depending on material properties and geometry.