List of Figures

• 2.1. The 96 minute XRISM orbit.
• 2.2. A schematic of the XRISM spacecraft. Resolve dewar and its XMA are highlighted in blue, while the Xtend instrument and its XMA are highlighted in pink. Image credit: JAXA.
• 2.3. Schematic layout of the two scientific instruments on-board XRISM, Resolve and Xtend. This is the view looking toward the sky from the back of the focal plane.
• 4.1. Image of the XMA with all its components.
• 4.2. Picture of the X-ray Mirror Assemblies, without thermal shields (right: Resolve-XMA, left: Xtend-XMA).
• 4.3. Major reflection paths occurring in the XMA structure. (a) Normal double reflection of the X-ray arriving from the on-axis direction. Incident X-rays are bent by the angle 4$\tau$ in total, and converge to the on-axis focus: (b) Secondary reflection, which arrives at the focal plane only if the incident angle of the X-ray, $\theta$, measured from the optical axis is in the range $\tau < \theta <2 \tau$: (c) Stray light path that gives rise to the brightest ghost among various backside reflections, the reflection at the backside of the primary followed by the normal double reflection. This pattern occurs when the X-ray incident angle is in the range $2\tau < \theta <3 \tau$. From Mori et al. (2005).
• 4.4. Image of a Pre-collimator quadrant used for XRISM XMA.
• 4.5. Image of a thermal shield quadrant used for XRISM XMA.
• 4.6. Cartoon view of the actual configuration of a mirror compared to the ideal geometry (shown on the left). The middle picture illustrates the shift between the focal point and the detector aim point and the right picture shows in addition the effect of a tilt of the optical axis with respect to the nominal aim-point direction (HITOMI in-flight calibration plan, 2015.)
• 4.7. Left: Layout of Xtend FoV (black) superimposed with Resolve FoV (cyan). This is a look-up view. The expected Xtend aimpoint is located from $\sim$5.0$^\prime$ (DETX) and $\sim$ 5.4$^\prime$ (DETY) from the edges of the CCD. The ground calibration reported that Xtend is on-axis at aim point (less than 3" shift). Right: The expected aimpoint of Resolve as the center of Resolve FoV. The ground calibration reported that optical axis of the XMA-Resolve is slightly shifted. In-flight calibration is on-going.
• 4.8. Effective area versus energy, for Xtend-XMA (black) and Resolve-XMA (red) plotted on the linear scale (left) and on the log scale (right). Note that these simulated curves are based on ground measurements and the XMA-only effective areas, thus not including QE of the detectors, etc..
• 4.9. Left: Vignetting curves of all energies, for Xtend-XMA, for azimuthal 0-180 deg, fitted with the sum of Lorentzian and Gaussian models to the data measured on the ground. Right: Look-down illustration of the mirror roll angle (different from the spacecraft roll angle) and the off-axis angle used during the ground calibration measurements (see Boissay-Malaquin et al. (2022)). The coordinates of the satellite and detector are shown, as well as the boundaries of the XMAs' quadrants.
• 4.10. Vignetting curves of all energies, for Resolve-XMA, for roll angle (azimuthal angle) 0-180 deg, fitted with 1D Lorentzian model fitted to the data measured on the ground.
• 4.11. Vignetting curves at 6.4 keV fitted to the data points measured on the ground, for Resolve-XMA (left) and Xtend-XMA (right), for 8 roll (azimuthal) angles (see the right panel of Figure 4.9).
• 4.12. Field of View of the XMAs, as a function of energy. The FoV is defined here as the FWHM value determined by fitting the vignetting curves with a 1D Lorentzian model, and does not take the physical size of the detectors into account. The FoV is the average value of the FWHM in all directions. The data points are from the ground measurements.
• 4.13. Focal plane images of Resolve-XMA (top) and Xtend-XMA (bottom) at the six energies of 1.49, 4.50, 6.40, 8.05, 9.44, and 11.07 keV (Tamura et al., 2022). The image size is 6.7$^\prime$ $\times$ 6.7$^\prime$.
• 4.14. One-dimensional PSFs of Resolve-XMA (left) and Xtend-XMA (right). The six PSFs at 1.49 (red), 4.50 (green), 6.40 (blue), 8.05 (light blue), 9.44(violet), and 11.07 keV (dark blue) are plotted (Tamura et al., 2022). These plots are based on the ground measurements.
• 4.15. The EEF of the Resolve-XMA (left) and the Xtend-XMA (right). The six EEFs at 1.49 (red), 4.50 (green), 6.40 (blue), 8.05 (light blue), 9.44 (violet), and 11.07 (dark blue) are plotted (Tamura et al., 2022). These plots are based on the ground measurements.
• 4.16. Stray light images of Resolve-XMA (top) and Xtend-XMA (bottom) at 30$^\prime$ off axis angle (left) and 60$^\prime$ off axis (right) (Tamura et al., 2022). The X-ray energy is 1.49 keV. The image size is 17.8$^\prime$ $\times$17.8$^\prime$. The FOV of Resolve is shown in left top panel.
• 5.1. A schematic of the Resolve microcalorimeter array focal plane. Dimensions shown are the design values, but most actual absorbers were 0.818 mm wide, and the gaps were correspondingly smaller on average.
• 5.2. Effective area of Resolve, which includes the gate valve transmission (Midooka et al., 2021).
• 5.3. Transmission curve for the non-selectable five-filter blocking filter stack.
• 5.4. The concept of an X-ray calorimeter is shown in the left panel, whereby an X-ray deposits energy in an absorber that is measured by a thermometer after the energy thermalizes. Subsequently, the absorber returns to its quiescent temperature and the system is ready to detect and measure the next X-ray. Right panel shows a schematic of the temperature of an absorber, which is a part of Resolve pixels, as a function of time. Upon absorbing the photon, the temperature goes up proportionally to the energy of the incident photon, and then goes down with time constant proportional to the heat capacity and thermal link conductivity.
• 5.5. Schematic arrangement of the XRISM Resolve microcalorimeter array and the anti-coincidence detector (c.f. Porter et al., 2010). The microcalorimeter array sits on top of the anti-co detector.
• 5.6. Typical shape of a pulse triggered by an incident X-ray. Left panel shows a single photon, while right panel shows a situation where second photon is detected before the pixel equilibrates after the first event. The undershoot following the pulse happens because the electronics are AC coupled. For details, see Section 5.3.1.
• 5.7. Comparison of the fluorescent Mn Ka spectra for different event grades from the Resolve ground calibration program.
• 5.8. Sketch illustrating the grading of Resolve events. The five cases described in the text (high primary, medium primary, medium secondary, low primary, and low secondary) are considered. For details see Ishisaki et al. (2018).
• 5.9. The event grade branching ratio is changed by the incoming rate. At low rates, most events will achieve calorimeter resolution ($H_p$ or $M_p$). For bright sources, resolution is degraded.
• 5.10. Instrument response to a monochromatic emission line at 5.414 keV, demonstrating the Gaussian core which dominates the line shape and the electron loss continuum. For more details, see Eckart et al. (2018)
• 5.11. Spectrum of the NXB background measured in-orbit in the Hitomi SXS microcalorimeter. For details, see Kilbourne et al. (2018a).
• 5.12. Filter wheel filter configuration arrangement, viewed looking up from the detector toward the sky.
• 5.13. Transmission curves for the selectable filters, the Neutral Density (ND) and Be-filter. For filter effective area curves see Figure 8.3.
• 6.1. X-ray images of the Perseus cluster obtained with the Hitomi observatory (Nakajima et al., 2018). (a) Full X-ray CCD (SXT+SXI) image overlaid with the micro-calorimeter (SXT+SXS) FOV in cyan. (b) Magnified CCD image of the central region overlaid with the SXS pixel boundaries in cyan. (c) Micro calorimeter (SXT+SXS) image of the same region.
• 6.2. Left — Schematic layout of the SXI CCDs looking toward the sky from the back of the focal plane. The 4 CCD chips are aligned in a 2$\times$2 format. Each CCD has two electrically separated segments, whose boundary is shown by the dashed line. Each segment has two readout nodes for redundancy (the black dots with the A/B/C/D labels). Each chip has an additional frame store area on the readout node side. The filled gray half circles show approximate areas illuminated by the calibration sources. The red box shows the SXS FOV and the dotted orange circles show the off-axis angles. The distances from the CCD edges are inflight measurement values. There is a tiny area on the far side corner from the aim point shown in yellow, where a camera body structure blocks the view of the sky. Right — SXI CCD sensor photo (Nakajima et al., 2020, Fig. 4). Gold-coated metal frames cover the frame store areas.
• 6.3. Left — SXI CCD Quantum efficiency measured with the ground experiments (black). The plot also separately shows the quantum efficiency of a CCD chip combined with the transmission of the Optical Blocking Layer (QE + OBL, red) and the transmission of the Contamination Blocking Filter (CBF, green). Right — Effective area of the Xtend telescope, including the XMA component.
• 6.4. Left — Hitomi SXI NXB spectrum normalized by the physical pixel area. The plot also shows a Suzaku XIS-BI NXB spectrum for the same physical pixel area. Right — Hitomi SXI total (NXB + sky) background spectrum normalized by the effective area and solid angle of the sky. The plot also shows the CXB spectrum and background spectra of other X-ray CCD instruments (Nakajima et al., 2018).
• 6.5. Simulated SXI image of the Perseus cluster with the 1/8 window mode. The green boxes show the approximate chip boundaries.
• 6.6. External View of SXI-S
• 6.7. Schematic diagram of the charge transfer process on a CCD. (a) At the end of a frame exposure, X-rays or charged particles produce charge clouds around the reacted pixels (red dots). (b) The CCD clock driver transfers the charge clouds vertically to the FS region. It also injects artificial charges to the top serial register every $N$ vertical transfers ($N$ =80 in the prelaunch default setup), which move down to the IA with the subsequent vertical transfers (red lines). (c) Once all IA charges move to the FS area, the CCD clock driver only transfers charges in the bottom FS row horizontally for readout and then moves all FS charges down by one pixel for another horizontal readout. It repeats this process until all FS charges are read out. IA takes another exposure during this readout process. (d) Another charge transfer process begins. The CI spacing and X-ray cloud sizes are not to scale.
• 6.8. Results of a ground test of charge injection (CI) operation in September 2021 with an SXI-S CCD engineering model. In this test, 5 keV charges were injected to the CCD chip by every 80 binned rows. Left — Peak Pulse Height (PH) values of Mn K$\alpha$ source events with/without (red/black) CI with the ACTY row, equivalent to twice the number of parallel transfers. CI prevents PH (i.e. charge) reduction. It produces a saw-tooth pattern because it works better on pixels following near a CI row. Right — $^{55}$Fe radioactive source spectra accumulated from all events on the CCD chip. CI recovers the line energy and the energy resolution.
• 6.9. 55Fe calibration source spectrum, obtained during the thermal vacuum test in August 2022.
• 7.1. Shape of the PSF and its effective impact on Resolve. Top panels: case of a point-like source placed at the center of the field of view (left), translating into significant internal SSM on the Resolve pixels (right). Bottom panels: case of a point-like source placed directly outside of the field of view (left), translating into significant external SSM on the Resolve pixels (right). “BL-CCD” stands for “Beam-Line CCD”.
• 7.2. Simplistic case of spatial mixing for a circular extended source whose left and right halfs are redshifted and blueshifted, respectively (uppermost panel). The two intermediate panels show, from that region (grey dotted circle), a distribution of all the incoming (redshifted or blueshifted) photons eventually reaching the Resolve detector (with yellow square and dashed lines lines indicating the Resolve detector boundaries).The XRISM PSF effectively mixes photons from each part into the other, resulting in 15-17% of cross-contamination (two bottom panels, showing the fractional number of photons).
• 7.3. Spectral mixing effects on the Fe-K line at 6.4 keV as seen by Resolve, assuming the simplistic case presented in Figure 7.2 (V1 = -235 km $s^{-1}$; V2 = +235 km $s^{-1}$). The top four panels assume a line width of $\sigma = 1$ eV (FWHM = 110 km $s^{-1}$), separating cases for contamination of equal fluxes (left panels) vs. cross-contamination of 16% representing the regions shown in Figure 7.2 (right panels), as well as theoretical models (upper panels) vs. more realistic profiles convolved by the Resolve RMF (lower panels). The bottom four panels show the same effect for a larger line dispersion width ($\sigma$ = 4 eV; FWHM = 440 km s$^{-1}$).
• 7.4. Illustration of the tasks performed by the routine xaarfgen—and the utility of the latter in computing SSM coefficients for the analysis of extended sources.
• 8.1. Electrical cross-talk “child” pulses occur in electrically adjacent pixels, so the cross-talk distribution does not follow the shape of the PSF. Left: Resolve pixel map showing electrically neighboring pixels. A parent pulse in pixel 18 (blue) will produce a child pulse in pixel 19 (light blue), but not in pixel 17 because it is in a different and electrically isolated quadrant. Likewise, a parent pulse in pixel 31 (orange) will produce child pulses in both pixels 30 and 32. Right: Cross-talk pulses (blue) have a shape based on the time derivative of the parent pulse (red) and a much smaller signal, with a peak amplitude of 0.6% of the pulse height. The child pulses are superimposed on the data stream in their pixels; when a child pulse in pixel 19, induced by a parent pulse in pixel 18, occurs around the same time as a parent pulse in pixel 19, the pulse shape is distorted. This leads to an erroneous energy measurement.
• 8.2. Left: Increasing contamination by cross-talk child pulses both broadens lines and shifts their centroids. At high count rates, this can significantly alter the energy resolution in individual pixels, as shown here for an example Fe K$\alpha$ line. Right: As an example, this Resolve pixel map shows the energy resolution (i.e., broadening) in each pixel when starting from $\Delta E$ = 5 eV and observing a source four times brighter than the Crab Nebula at the array center. The four exterior pixels with the worst resolution are electrically adjacent to the central four pixels. Note that the map is not weighted by the event rate or grade: despite the better energy resolution in the central pixels, there are hardly any Hp+Mp events from those pixels.
• 8.3. Resolve effective area curves with the gate valve closed for no filter (black), the Be filter (red), and the neutral-density filter (blue). The neutral-density filter reduces the count rate by about a factor of four across the bandpass. For filter transmission curves see Figure 5.13. The Be filter is optimized for suppressing (continuum) events at low energy in favor of preserving high-resolution events in the Fe-K complex.
• 8.4. These six plots show a mock image (top left), raw incident count rate (top center), processed Hp+Mp rate (top right), cross-talk child pulse rate (bottom left), effective spectral resolution (bottom center), and centroid shift (bottom right) in each pixel for a $10^{-7}$ erg s$^{-1}$ cm$^{-2}$ source observed no filters. The top right quadrant is sacrificed to maximize the Hp+Mp rate in the other three quadrants, as each quadrant is processed separately in the PSP.