XRISM
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XRISM SOC-PVO

Releases•

2202-02-22 Version 2.1 (N. Ota, T. Mizuno, H. Uchiyama, theXRISM SOC-PVO team)•

2022-02-04 Version 2 (N. Ota, T. Mizuno, H. Uchiyama, theXRISM SOC-PVO team)•2020-10-06 Version 1 (N. Ota, T. Mizuno, H. Uchiyama, theXRISM SOC-PVO team)Table of Contents
I. OVERVIEW ................................................ 1
I-1. XRISM Mission ........................................................... 1
Overview .................................................................. 1
Scientific objectives .................................................... 1
Key technologies ........................................................ 1
I-2. Spacecraft & Components ............................................ 2
I-3. Parameters ................................................................ 3

II. INSTRUMENTS ......................................... 4
II-1. X-ray Mirror Assembly ............................................... 4
Basics ...................................................................... 4
Technology ............................................................... 4
Performance .............................................................. 4
II-2. Resolve .................................................................... 6
Basics ...................................................................... 6
Technology ............................................................... 6
Performance .............................................................. 6
Observation modes .................................................... 7
II-3. Xtend ...................................................................... 9
Basics ...................................................................... 9Technology ............................................................... 9
Performance ............................................................ 10
Observation modes .................................................. 10

III. FIGURES OF MERIT .............................. 11
III-1. Effective Area ........................................................ 11
III-2. Energy Resolution .................................................. 12
III-3. FoV and Grasp ....................................................... 13

IV. CASE STUDIES ...................................... 14
IV-1. Black Holes ............................................................ 14
IV-2. Supernova Remnants .............................................. 16
IV-3. Clusters of Galaxies ................................................ 18

FURTHER INFORMATION ............................ 20
Web page ............................................................... 20
References .............................................................. 20
Points of Contact ...................................................... 20
Science cases ................. Error! Bookmark not defined.

I. Overview

I-1. XRISM Mission
Overview
The X-ray Imaging and Spectroscopy Mission (XRISM) is an X-ray
observatory, which is the 7th in the series of the X-ray observatories fromJapan. The mission of XRISM is to recover and resume the study of theprime objective of ASTRO-H/Hitomi “to solve outstanding astrophysicalquestions with high-resolution X-ray spectroscopy”. It is currently planned
to be launched in FY2022 with an HII-A rocket from the Tanegashima
Space Center, Kagoshima, Japan.
Launch site

Tanegashima Space Center

Launch vehicle

JAXA HII-A rocket

Orbit altitude

550±50 km

Orbit type

Approximately circular orbit

Orbit inclination

31 degree

Dimension

7.9 m x 9.2 m x 3.1 m

Mass

2.3 metric ton

Mission life

3 years + cryogen free
operation

Fig. 1 Artist's drawing of the
XRISM satellite.

Scientific objectives•

Revealing the structure formation of the Universe and evolution ofclusters of galaxies•

Understanding the circulation history of baryonic matters in the
Universe•

Investigating the transport and circulation of energy in the Universe•

Realizing the new science with high-resolution X-ray spectroscopy

Key technologies•

An X-ray micro-calorimeter detector which enables high resolution (≤7 eV) spectroscopic observations between 0.3 and 12 keV•

An X-ray imager detector which enables a wide-field imaging
spectroscopy between 0.4 and 12 keV

1

I. Overview

I-2. Spacecraft & Components

X-ray Mirror Assembly (XMA)
Xtend-Soft X-ray Imager

Resolve-Soft X-ray Spectrometer

Fig. 2 Schematic view of the XRISM satellite.There are two focusing X-ray
telescopes mounted at a fixed optical bench. They will focus X-rays onto focal plane
detectors mounted on the base plate of the spacecraft.

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I. Overview

I-3. Parameters
Table 1 Key parameters and performance requirement of the XRISM observatory(Tashiro et al. 2018)

Parameters

Resolve

Xtend

X-ray mirrors

Conically approximated Wolter I optics (203nested)Focal length

5.6 m

Angular resolution≤ 1.7 arcmin (HPD*1)

Detector technology

X-ray microcalorimeter

X-ray CCD

Effective area

≥210 cm2 @ 6keV,≥160 cm2 @ 1keV

≥300 cm2 @ 6 keV

Field of View

≥ 2.9 x 2.9 arcmin2≥ 30 x 30 arcmin2

Energy range

0.3 – 12 keV

0.4 – 12 keV

Absolute energy scale≤ 2 eV–

Energy resolution≤ 7 eV FWHM @ 6keV

≤ 250 eV @ 6keV
(EOL)

Non X-ray background≤ 2 x 10-3
c/s/keV/array≤ 1 x 10-6
c/s/keV/arcmin2 (in 5–
10 keV)Time tagging accuracy≤ 1 ms–*1 Half Power Diameter3II. Instruments

II-1. X-ray Mirror
Assembly
BasicsXRISM has two identical X-ray Mirror Assembly (XMA). One
is for Resolve and the other for Xtend. XMA is similar inconcept to the X-ray telescope (XRT) of Suzaku (Table2). It is composed of 203 thin reflector shells tightly
nested confocally and coaxially (Fig. 3). A conicalapproximation of Wolter-I optic is used.

Fig. 3 Schematic view of
XMA. The blue and red parts
are the mirror housing and
Pre-Collimator, respectively.

Table 2 Comparison of XRISM/XMA and Suzaku/XRT
No. of tele
scope

Focal length(m)

Diameter(cm)

No. of nested
shells

HPD (arcmin)

XMA

2

5.6

45

203

1.3

XRT-I

4

4.75

40

175

2.0

*1A

Aeff*1
(cm2)
560
425
470
320

eff is the on-axis effective area (mirror only) at 1 & 6 keV. Source extraction radius is infinite, or 100% photons
are encircled. The values correspond to one unit.

Technology
Three different thicknesses of Al substrates (152, 229, and 305 μm) areused, in which the outer shells use the thicker substrates. This is intended
for achieving a large collecting area with a better imaging quality than
Suzaku/XRT. The considerably better HPD than XRT (Table 2) is realizedby fixing the reflectors to support bars with adhesive. Stray light orcontaminating X-rays from outside of the field of view, is reduced by astray-light baffle, called Pre-Collimator, which consists of coaxially-nested
cylindrical aluminum blades placed above each reflector. A thermal shield
is attached in front of the Pre-Collimator to stabilize the thermal
environment of the XMA. The shield is made of Al-coated Polyimide film toensure a large effective area in the soft energy band.

Performance
The XMA’s effective area at on-axis and off-axis angles and the encircled
effective area are shown in Fig. 4 and Fig. 5, respectively.

4

Fig. 4 Effective area (mirror only) as a function of energy at on-axis and some off-axis
angles. The source extraction radius is 1.8 arcmin (78% encircled energy fraction). Notethat this is a mirror-only effective area. Fig. 14 shows the actual effective areas combinedwith detectors.

Fig. 5 Encircled effective area, representing the sharpness of an image at several
energies at on-axis and some off-axis angles.

5II. Instruments

II-2. Resolve
BasicsResolve spectrometer is equipped with an X-ray
microcalorimeter array of 6x6 pixels at the focus of
the X-ray mirror assembly (XMA), which is capableof non-dispersive high-resolution (∆E≦7 eV)
spectroscopy and limited imaging of 3’ x 3’ field ofview in the soft X-ray (0.3-12 keV) band with a large
effective area of ≧210 cm2.

Fig. 6 Concept of X-ray
micro-calorimeter

Technology
The detector measures the temperature rise upon each incident X-ray
photon, achieving an unprecedented energy resolution. The thermometeris made of HgTe absorbers of an 8 μm thickness on micro-machined, ionimplanted Si wafer. The anti-coincidence Si semiconductor detector
enables rejection of background events. The 50 mK operation
temperature in the dewar is achieved by the cooling system comprised ofadiabatic demagnetization refrigerators, He coolants, and mechanicalcoolers. The cooling system allows redundancy and cryogen-free
operation. The filter wheel provides a suite of attenuation filters toenhance the dynamic range of the Resolve for bright sources. The
modulated X-ray source (MXS) will be used for accurate energy-scalecalibration in orbit.

Performance
Since the Resolve is a non-dispersive spectrometer, it can be used toobtain high-resolution spectra of both point and extended sources (Fig.
7). The effective area of >200 cm2 at the Fe K-band is considerably larger
than any other high-resolution spectrometers. The imaging capability islimited as the HPD is comparable to the FoV (Fig. 7). Since the HPD islarger than the pixel size (~30”), there is a cross-contamination effect by
the PSF. A simulation tool (e.g., heasim) estimates this effect for an
observation target with multiple sources or an extended source withspatial variation in its spectrum.

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The non-X-ray background (NXB) level after anti-coincidence screening
should be lower than 2x10–3 counts/s/keV, which corresponds to 1.4
counts/(100 ks)/(7 eV). The major sources of the NXB are particles
hitting the detector pixels, those hitting the support frame around the
pixel array ("frame events"), and electrical crosstalk. The electricalcrosstalk has a few 10-100 times smaller pulse height than its parental
event, and therefore it is only a potential background component at very
low energies in hard X-ray sources.
The Modulated X-ray Source (MXS) produces pulsed X-rays with ~a few
ms pulse length and ~a few 100 ms pulse spacing, and provides
fluorescent X-ray lines, mainly Cr Kα at ~5.4 keV and Cu Kα at 8.0 keV,for the gain tracking. When the MXS is used, MXS pulse-on time intervals
are removed by a good-time interval (GTI) file computed by a dedicatedtool. This leads to a small amount of loss of observing efficiency. Because
MXS pulses have exponential tail, there are non-zero MXS events inpulse-off intervals. This contaminates GTI-screened data and contributes
as another component of the background for Resolve. One of the pixels("cal-pixel") is located outside the FoV and is illuminated by a Fe-55
source to monitor overall temporal gain drift of the detector. The calpixel, together with another Fe-55 source on the filter wheel, adds
redundancy to the gain calibration.

Fig. 7 Pixel layout (upper left panel). The array encompasses ~74% of photons of apoint source at the center. Simulated spectrum of Centaurus cluster (bottom left).

Observation modes
Resolve has only one science observation mode. All X-ray events are
graded based on intervals of event trigger times, which are determined by7

processing individual event pulse records (Fig. 8). Calorimeter resolution(ΔE≦7 eV) is guaranteed only for high-res (Hp) and mid-res primary(Mp) events. The digital processor (PSP) is capable of handling only up to
200/s ~ 120 mCrab (“PSP limit”; see Fig. 9). For bright sources, it isbeneficial to intentionally reduce the incoming photons using filters (Fig.
10), offset pointings, or a combination of these.

Fig. 8 Grade definition. The figure illustrates spacings of event pulses (shown withtriangular shapes) corresponding to the five event grades: high-res (Hp) if there is no
event triggered within ±70.72 ms; mid-res (Mp and Ms) if there is no event within±18.32 ms; else low-res (Lp and Ls). "p"=primary denotes the earlier event of an event
pair, while "s"=secondary denotes the later one. The minimum separations to distinguish
the grades (70.72 ms for mid-res vs. high-res and 18.32 ms for low-res vs. mid-res) aredetermined primarily by the length of per-event pulse record that is required by the PSP
to perform the signal processing called the optimal filter.

Fig. 10 Filter selection. The filter wheel
has three filters, two open positions, andone position with a radioactive Fe-55
calibration source. The three filters are
Beryllium filter (Be), neutral-density
filter (ND), and polyimide filter (Poly).

Fig. 9 Incoming vs. processed rate for
Hp+Mp events (solid). Because of thelimitation in the CPU load (“PSP limit”),
the processed rate is reduced from what
would otherwise be observed (dotted).
The calculations do not include the effectof electrical crosstalk.

8II. Instruments

II-3. Xtend
Basics
Xtend is a telescope system which consists of an X-ray mirror assembly(XMA) and an X-ray CCD camera (SXI) [5]. It has an imagingspectroscopic capability with a wide FoV (38x38 arcmin2) and a medium
energy resolution (E/∆E~35@6 keV, based on the performance ofHitomi/SXI [7]) in the soft X-ray band (0.4-13 keV). It is a successor of
Suzaku/XRT+XIS and Hitomi/SXT+SXI (Table 3).
Table 3 Comparison of XRISM/Xtend and Suzaku/XRT+XIS.

Xtend
XRT
+XIS

No. of
CCD

No. of
tele
scope

4
4

Layout

Pixel
scale

FoV *1(arcmin2)

1

2x2
array

1.77’’

38x38

4

4 coaligned

1.04’’

18x18

Aeff*2
(cm2)

374
356
694
797

Grasp
(cm2
arcdeg2)

Frame
time (s)Illumination

Type

54

4

BI*3 x4p-chan200

8

FI*4 x3
BI*3 x1n-chan80 (FI)
40 (BI)

35

Depl. layer(μm)

As the values of Xtend, the in-orbit performance of Hitomi/SXT+SXI is listed here. *1FoV for the
2x2 array for SXI. *2Aeff is the on-axis effective area at 1 & 6 keV. The integration region is a
circle with the radius of 1.8 arcmin. Four CCDs combined for XIS. *3Back-illuminated CCD.
*4Front-illuminated CCD.

Technology
The p-channel CCDs have a thick depletion
layer to extend the hard-band coverage. The
thick depletion layer will also reduce thebackground above ~7 keV compared to thesame back-illuminated (BI) CCD in XIS. The
BI CCDs have high quantum efficiency in thesoft X-ray band. They are also more resistantFig. 11 External view of
Xtend/SXI

than the FI CCDs to micro-meteorite hits. To
decrease charge transfer inefficiency (CTI), a charge injection structure isequipped. It injects artificial charge to pixels periodically to fill traps whichcause CTI. Mechanical coolers are used to keep the device temperature at-120 deg C. To suppress contamination accumulation on the CCD chips, acontamination blocking filter is placed on top of the hood. Onboard
calibration sources (55Fe) illuminate the corners of the CCDs. The designof Xtend is almost identical to that of Hitomi/SXT+SXI (Fig. 11) but some9

updates are introduced to solve the problems (e.g., optical light leak)found in the orbital operation of Hitomi [5].

Performance
The 2x2 CCD array covers a very large FoV. The on-axis position is 7.2'
offset from the Xtend center. Xtend has a moderate energy resolution(Fig. 12). Like Suzaku/XRT+XIS and Hitomi/SXT+SXI (Fig. 13) [8], thebackground of Xtend is expected to be low and stable, benefiting from thelow-earth satellite orbit.

Observation modes

CCD clocking modes with different exposure times (4, 0.5, and 0.06 s)
will be supported to mitigate CCD pile-up. The pile-up limits for each of
the exposure time modes are about 1, 9, and 90 mCrab, respectively.

Fig. 12 55Fe Spectrum of a FM CCD chip in a ground calibration.

Fig. 13 Comparison of the sky background of X-ray CCD cameras [8]10III. Figures of Merit

III-1. Effective Area

Fig. 14 On-axis effective area of XRISM
telescopes & detectors, Resolve (red)and Xtend (green). For Xtend, the inorbit performance of Hitomi/SXT+SXI isplotted here.

Fig. 15 Resolve on-axis effective areawith filter: the open filter (red), neutral
density filter (black), 25um Be filter(blue).

Fig. 16 On-axis effective area of XRISM (Resolve, Xtend), Suzaku (XIS-BI+XIS-2FI,
HXD), Chandra (ACIS-S), XMM-Newton/EPIC (PN+MOS1+MOS2), and NuSTAR.

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III. Figures of MeritIII-2. Energy Resolution(i) Strong line: FOM ~ √A(ii) Weak line: FOM ~ √(A/ΔE)(iii) Strong line: FOM ~ √(AE2/ΔE2)(iv) Weak line: FOM ~ √(AE2/ΔE3)(v) Strong line: FOM ~ √(AE4/ΔE4)(vi) Weak line: FOM ~ √(AE4/ΔE5)

Fig. 17 Figures of merit (FOM) for (i) detection of strong line, (ii) detection of weak line,(iii) velocity of strong line, (iv) velocity of weak line, (v) broadening of strong line, (vi)broadening of weak line. Strong lines are defined here as lines with equivalent width W
larger than the instrumental resolution ΔE, weak lines have W smaller than ΔE.

12

III. Figures of MeritIII-3. FoV and Grasp

Fig. 18 Field of view of the XRISM instruments, Resolve and Xtend (the blue boxes).
Chandra ACIS-I and XMM are also shown for comparison. The background image is theComa cluster taken with ROSAT (credit: ROSAT/MPE/S. L. Snowden).

Fig. 19 Grasp vs on-axis effective area at 7 keV of Resolve and Xtend. Suzaku XIS,
Chandra ACIS-I, XMM PN are also shown for comparison. The grasp is defined as the
product of field of view and effective area.

13IV. Case Studies

IV-1. Black HolesXRISM provides an unprecedented view of the motions and extreme
physical conditions of matter near the event horizon. This will help us
unravel how black holes grow by accreting gas and simultaneously shape
their environments via the intense radiation fields and powerful,
sometimes relativistic outflows that accompany this accretion.
Gaseous winds driven from black hole disks can carry away a substantial
fraction of the gas that would otherwise accrete onto the central black
hole. Such winds are hot, and most easily detected in the Fe K band via
absorption lines. As shown in Fig. 20, the superior resolution of Resolvein the Fe K band enables the unambiguous detection of weak and narrowlines from a wind. We will be able to use these to precisely determine theradius at which the wind is launched, and the mass outflow rate carriedby it. This will give us strong constraints on the driving mechanism of thewind and its feedback on the accretion flow.
XRISM will also give us key observations to investigate the feeding andfeedback mechanisms in supermassive black holes (SMBHs) at galactic
centers, and thereby the origin of SMBH-galaxy coevolution. Cold mattersurrounding an active galactic nucleus (AGN), called the “torus”, serves
as a mass reservoir linking the SMBH and hostgalaxy. Outflows of warm photoionized gas by the central radiation carrysignificant mass, momentum, and energy outward, which have strong
impacts on its environment.
XRISM will provide us with an unbiased view of mass distribution andkinetics of surrounding matter, through observations of fluorescence lines
from the cold torus and absorption/emission lines from highly ionizedoutflows. As shown in Fig. 21, Resolve enables us to separate andcharacterize many emission lines from different locations, which tell us
the physical origins of these phenomena.

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Fig. 20 A simulated spectrum of the black hole GRS 1915+105 with a 40 ks Resolve
observation. The model is based on a prior Chandra observation (Miller et al. 2020).

Fig. 21 A simulated spectrum of the obscured AGN Mrk 3 with a 200 ks Resolve
observation. The model is based on a prior Suzaku observation (Awaki et al. 2008).

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IV. Case Studies

IV-2. Supernova Remnants
The high-resolution spatially-resolved X-ray spectroscopy provided by
Resolve will be particularly ground-breaking for supernova remnants(SNRs) because they are extended objects with rich emission-line spectrafrom a wide range of different elements (carbon through nickel). The
following examples highlight some of the topics that XRISM will address.
(1) Understanding the progenitors of various kinds of SNRs
Low-abundance elements such as Ti, Ni, Cr, Mn are the key elements todetermine the physical condition of the stellar core at the moment of
explosion. XRISM will resolve emission lines from all four of theseelements and measure their total abundances, placing constraints on how
the original supernova explosion progressed (Fig. 22). The velocity of therapidly expanding supernova ejecta, as well as the circumstellar andinterstellar gas it sweeps up will also be measured by XRISM via Doppler
shifts. Such velocity measurements reveal how SNRs evolve, based on
their age and the detailed properties of the explosion, the ejecta, andambient medium.
(2) Understanding the physics of collisionless shocks in SNRs
Collective interactions between particles and electromagnetic fields are
responsible for shock formation (collisionless shocks) and energy
redistribution. XRISM will resolve this heating process, as it impacts
electrons, protons, and heavier elements. Shocks accelerate someparticles into the TeV range, believed to be the origin of Galactic cosmic
rays, and these particles extract energy from the shocks. XRISM willmeasure the fraction of the shock’s energy that goes into accelerating
particles and the particle acceleration efficiency.
(3) Understanding Radiative processes of hot plasmas
There are many details in the X-ray spectra of hot plasmas that remain
unexplored due to the limited capabilities of the current generation of Xray spectrometers. XRISM will show us the first precise measurements of

16

the plasma in various states, ionizing or recombining, and various effects
such as resonance scattering and charge exchange (Fig. 23).

Fig. 22 100ks simulation of western half of 3C397. Several lines via Ni and Fe L-shellemission are seen for example at 1.045,1.156 keV for Ni and 1.01 keV for Fe,
respectively as well as peaks from K-shell transition of Si (1.84 keV) and Mg (1.33 keV).

Fig. 23 30-ks simulated Resolve spectra of a shell region of the Cygnus Loop. Top:
Assumed model is a typical thermal plasma with electron temperature of 0.2 keV.
Middle: Same as the top panel but added a charge-exchange model in XSPEC. Bottom:
Same as the middle panel but simulated in SPEX with similar model parameters.

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IV. Case Studies

IV-3. Clusters of Galaxies
The dominant baryonic component of galaxy clusters is in a form of hot
intergalactic gas. Shocks produced by violent mergers of clusters andmatter accretion, feedback from Active Galactic Nuclei (AGNs) heat thegas to very high temperatures. With its calorimetric energy resolution, theResolve will detect individual spectral lines emitted by the hot gas,allowing the measurements of turbulence and gas flows generated during
these events. The low-background Xtend will map the gas thermal state
in cluster outskirts. These measurements are crucial for understanding
the evolution of the largest objects in the universe and precise cluster
cosmology.
Feedback from supermassive black holes
In nearby bright galaxy clusters, like the Virgo/M87 cluster, XRISM will
spatially and spectrally resolve the interaction between AGN andintracluster medium, allowing the studies of the mixing of different gas
phases and metals and probing gas dynamics close to the supermassive
black hole. White squares in Fig. 24 show the Resolve field of view.
Simulated 100-ks spectrum shows that the kinematics of two different
gas components can be measured using the Fe-L line complex.
Non-thermal pressure support for precise cluster cosmology
XRISM will measure turbulence contribution to the total pressure ingalaxy clusters significantly improving their mass measurements that are
crucial for precise cluster cosmology. Simulated Resolve spectrum fromthe region around r2500 in A2029 shows strong Fe lines broadened byturbulence (Fig. 25).

18

Fig. 24 Simulated 100-ks Resolve spectrum of M87 (black). Contributions from different
thermal components to the Fe-L line complex are shown (orange: hot atmosphere,
purple: uplifting gas,).

Fig. 25 Simulated 250-ks Resolve spectrum of the outermost A2029 pointing, P3’(black). Contributions from each annulus are shown in different colors (green: A1, blue:
A2, orange: A3), suggesting that correction for the contamination from the bright core isnecessary for the accurate turbulence measurement.

19

Further Information
Web page•

XRISM <http://xrism.isas.jaxa.jp>

References•

XRISM[1] Tashiro et al. 2018, SPIE, 10699, id. 106992•

Resolve[2] Kelly et al. 2016, SPIE, 9905, id. 99050V[3] Sato et al. 2016, JATIS 2d4001S[4] Kilbourne et al. 2018, JATIS 4a1214K
For subsystems and calibration, a comprehensive list is available:
https://heasarc.gsfc.nasa.gov/docs/hitomi/about/paper_list.html#jatis

•

Xtend
[5] Hayashida et al. 2018, SPIE, 10699, 1069923, SPIE10699[6] Nakajima, Hitomi Collaboration, 2017, NIMPA, 873, 16[7] Tanaka et al. 2018, JATIS, 4, 011211[8] Nakajima et al. 2018, PASJ, 70, 21•

Hitomi White Papers
https://heasarc.gsfc.nasa.gov/docs/hitomi/about/paper_list.html#whitep

Point of Contact•

Questions and comments to the documento

SOC-PVO <Z-xrism-soc-qref@ml.jaxa.jp>

20

Acknowledgement
A. Bamba, M. Diaz Trigo, M. Guainazzi, J. Kaastra, Y. Fujita, K. Matsushita, R.
Mushotzky, H. Nakajima, J.-U. Ness, M. Sawada, H. Uchida, Y. Uchida, Y. Ueda,
H. Yamaguchi, I. Zhuravleva

21