Combine Resolve and Xtend

XRISM carries Resolve and Xtend, each with its own focusing mirror assembly. Resolve emphasizes fine energy discrimination over a small field. Xtend maps a much wider field and helps identify nearby sources, diffuse emission and background around the target. Its CCDs also measure energies; the distinction is their different performance and observing roles, not that one instrument measures energy while the other never does.

Suppose a target lies near a second bright X-ray source. A spectrum extracted without examining the surrounding field might mix their signals. Xtend’s context can reveal the neighboring source and inform how the observation is modeled. Conversely, a wide image alone may not distinguish nearby narrow spectral features that Resolve separates.

The September 2026 JAXA research update describes Resolve still observing with its gate valve closed. The protective door reduces sensitivity at low X-ray energies. The current technical guide therefore describes a nominal calibrated range of about 1.7–12 keV, rather than treating the original wider design range as achieved performance. This limitation belongs to Resolve; it does not mean Xtend’s separate telescope is shut.

A target dominated by soft X-rays can be a poor match for the available Resolve configuration even while harder-energy features remain scientifically useful. An engineering limitation changes which questions are practical. It does not automatically mean every observation is useless or that all original capabilities have been recovered.

Plan with the available instrument

For an invented planning exercise, a selected feature produces 0.20 useful counts per second after screening. A 5,000-second good exposure yields an expected 1,000 counts. If only half of a 10,000-second wall-clock interval qualifies as good exposure, it gives the same expectation. A count is a detected event; an expected value is not a guarantee of an exact integer result in a real observation.

A bright source is not always easier. Nearby pulses can overlap, event grades can change and processing capacity can be exceeded. Shorter exposures alone do not reduce the instantaneous arrival rate. A suitable observing mode, attenuation or analysis selection may be necessary. Use the instrument guide for the actual target and configuration rather than assuming every detected event has identical spectral quality.