arcus:an x-ray grating spectrometer on the iss mission and

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Arcus leverages NASA’s investment in the off-plane gratings that have been in development at the University of Iowa for Constellation-X and IXO. Off-plane gratings have success-IXOO\�ÁRZQ�LQ�VXERUELWDO�URFNHW�ÁLJKWV��DQG�GHVLJQV�VLPLODU�WR�those planned for Arcus have been demonstrated at the NASA/MSFC stray light facility to reach R = h 6h�!�������OLPLWHG�E\�WKH�ÀQLWH�VRXUFH�size. The gratings will be housed in modules that will be paired to the silicon pore optics PRGXOHV��VLPSOLI\-ing assembly and alignment.

Arcus will observe the end products of structure formation in the form of hot gas beyond the virial radius of galaxies and FOXVWHUV��DV�ZHOO�DV�GH-WHFWLQJ�ÀODPHQWV�LQ�WKH�IGM itself via absoprtion WR�EDFNJURXQG�$*1��$V�VKRZQ�DW�ULJKW��RQO\�$U-cus has the sensitivity to GHWHFW�ÀODPHQWV�ZLWK�OHVV�than 4mÅ EqW. Arcus will also direct-O\�REVHUYH�IHHGEDFN�DQG�winds from supermassive EODFN�KROHV�LQ�WKH�IRUP�RI�warm absorbers with an order of magniture more sensitivity than Chandra RU�HYHQ�$VWUR�+��PHD-suring the velocity and temporal variations in the ionization structure of the jet (see Figure at right). Arcus will study stellar formation and evolution by GHWHFWLQJ�DFFUHWLRQ�ÁRZV�onto young stars as well as XVLQJ�ZHDN�EXW�KLJKO\�VHQ-sitive satellite line diagnos-tics that require high res-ROXWLRQ�DQG�HIIHFWLYH�DUHD��as shown at right. Observa-tions of Galactic XRB and EODFN�KROH�VRXUFHV�ZLOO�OHQG�insights into these systems DQG�WKH�VWUXFWXUH�RI�WKH�KRW�LQWHUVWHOODU�PHGLXP�DQG�KDOR�RI�WKH�0LON\�:D\��

Arcus Design

Arcus is an X-ray grating spectrometer mission to be deployed on the International Space Station in response to NASA’s Astrophysics Division plan to announce a SMEX call in Fall 2014

with a cost cap of $125M (FY15). The baseline design uses sub-apertured X-ray silicon pore optics feeding into off-plane gratings to achieve both high spectral resolution with a large effec-

tive area. The detector focal plane uses Suzaku-type CCDs. The mission would be ready to be launched and mounted on the ISS in 2020. The mission parameters are R>2500 with >650 cm2

at the critical O VII wavelength around 22-25Å (~0.5 keV), with an overall bandpass from 8-52Å (0.25-1.5 keV), enabling a wide range of science objectives. These values are similar to

those of the grating spectrometers considered as part of the proposed Constellation-X and IXO missions, which were highly ranked by two Decadal surveys.

Arcus:An X-ray Grating Spectrometer on the ISSMission and Science Overview

Randall K. Smith1��5��$OOXUHG1��0��%DXW]2��-D\�$��%RRNELQGHU1��-��%UHJPDQ3��/��%UHQQHPDQ1��1��%ULFNKRXVH1��'��%XUURZV4��9��%XUZLW]5��$��&DUULHU6��3��&KHLPHWV1��3��'DLJQHDX1��$��)DOFRQH4��A. Foster1��0��)UHHPDQ1��5��+HLOPDQQ2��%��+RZOH\6��'��+XHQHPRHUGHU2��-��.DDVWUD7��+��0DUVKDOO2��5��0F(QWDIIHU8��(��0LOOHU2��-��0LOOHU3��5��0XVKRW]N\9��)��3DHUHOV10��

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Arcus Optical & Detector Layout

10 20 30 40 50Wavelength (Å)

0

200

400

600

800

1000

1200

Effe

ctive

Are

a (c

m2 )

XMM-Newton RGSChandra Gratings

Astro-H SXS

Arcus~900 cm2

at O VII

~575 cm2 at C VI

~1000 cm2 from 9-16Å

4 Ir-coated SPO petals w/ O"-plane Gratings 96% open Silicon mesh #lter base 45 nm polyimide coating 70 nm Al optical blocking #lter Suzaku-type BI CCD QE

Conclusions

The Arcus science goals were highly regarded both by NASA and by the FRPPXQLW\��DV�UHÁHFWHG�E\�WKHLU�PHQWLRQ�LQ�WKH������1HZ�:RUOGV��1HZ�+RUL]RQV�'HFDGDO�6XUYH\��:LWK�(6$·V�GHFLVLRQ�WR�ODXQFK�$WKHQD�LQ������DV�WKHLU�/��PLVVLRQ��WKH�JUDWLQJ�VFLHQFH�UHPDLQV�DQ�H[FLWLQJ�RSSRUWXQLW\���The challenge has been to achieve those goals in a timely fashion and an affordable cost. Arcus is designed to meet the NWHN recommendations DQG�FXUUHQW�FRQVWUDLQWV�DW�DQ�H[WUHPHO\�DWWUDFWLYH�FRVW�WKDW�FDQ�EH�ÀW�ZLWKLQ�a SMEX mission by combining existing technology and the opportunities provided by the ISS.

Arcus leverages ESA’s investment in the silicon pore optics over the last decade. 7KHVH�RSWLFV�DUH�SODQQHG�IRU�XVH�LQ�$WKHQD�LQ�������ZLWK�DQ�LPDJLQJ�36)�UHTXLUH-PHQW�RI��··��DOWKRXJK�WKH�$UFXV�UHTXLUHPHQW�RQ�WKH�RSWLFDO�SHUIRUPDQFH�LV�FORVH�WR��··��:KLOH�LPSURYHPHQWV�LQ�WKH�RYHUDOO�LPDJLQJ�FDSDELOLWLHV�RI�WKH�RSWLFV�FRQWLQXH��nonetheless the current generation of 75/��RSWLFV�KDYH��WKH�UHTXLUHG�SHU-formance for use in a grating spec-WURPHWHU��$V�VKRZQ�LQ�WKH�ÀJXUH�DW�ULJKW��WKH�UHOHYDQW�LVVXH�LV�QRW�WKH�IXOO�36)��EXW�UDWKHU�WKH�QDUURZ�´WUDQV-YHUVHµ�36)�DORQJ�ZLWK�WKH�SKRWRQV�

will be dispersed. These data were from an older mirror module (top left) measured at the IRFDO�SODQH��UHVXOWV�IURP�WKH�FXUUHQW�JHQHUDWLRQ�RI�632�DUH�H[SHFWHG�WR�LPSURYH�$OWKRXJK�WKH�EHVW�PHDVXUHG�+(:�IRU�D�632�PLUURU�LV�DERXW����DUFVHF��WKH�GDWD�VKRZQ�KHUH�DW�ULJKW�ÀQG�D�����DUFVHF�):+0�LQ�WKH���GLPHQVLRQDO�SURMHFWLRQ�IRU�WKH�VKRUW�D[LV��ZKLFK�HTXDWHV�WR�MXVW�OHVV�WKDQ��µ�+(:���%HORZ�WKDW�SULPDU\�*DXVVLDQ��WKHUH�LV�D�VHFRQG�a�··�*DXVVLDQ�ZLWK�OHVV�DUHD���,Q�WKLV�VWXG\��WKH�SUREH�EHDP�KDV�D�GLYHUJHQFH�RI��µ��VR�D��µ�image is basically the geometrical limit. In short: the current silicon pore optics meet

the Arcus requirement.

Silicon Pore Optics

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XMM-Newton RGS

Chandra Gratings

Astro-H SXS

O VIII O VII C VINe IX N VII N VI

Athena (2028)

Arcus

5m�detection, 500 ksec obsUsing 25 blazar LOS with Fx~10-11 cgs

5mÅ (Athena systematics limit)

C V

3mÅ

10 20 30 40 50Wavelength (Å)

10

100

1000

Line

Det

ectio

n Fi

gure

of M

erit

FoM = [Resolving Power x E#ective Area]0.5 (cm)

Arcus Science

0 100 300200

100

300

200

X Position (24 µm pixel)

Y Po

sitio

n (2

4 µm

pix

el)

Silicon Pore Optic20 m focal length20 plates 6.5 cm2 geo. area Full HEW

~ 24 arcsec

Transverse HEW ~ 1 arcsec

Data courtesy cosine Research

Arcus

Chandra LETGS/HRC-S

Astro-H/SXS

NH

Det

ectio

n Th

resh

old

(cm

-2)

Log [Ionization Parameter j]-2 -1 0 1 2 3 41017

1018

1019

1020

1021

1m limit in 100 ksecDetecting warm absorbers in AGN

Optics Module

5.5m

Extendable & Collapsable Optical Bench (with shroud)

Arcus Layout (Deployed)

CCDs

Focus Mechanism,A/D Electronics,Thermo-Elec Cooler

~1m

TBD

DFP MountPoint (opt)

DFP MountPoint (opt)

2-axisGimbal

FRAM (active)

FRAM (passive)

International Space StationG

razi

ng In

cide

nce

Opt

ics

O!

Plan

e G

ratin

g M

odul

es

IncomingX-rays

FineSun

Sensor

Re-closableDoor

(Mass ~ 120 kg,~1m x 1m area)

(Mass ~ 20 kg)Science Instrument Module

with opticalbench stowed

~500mm

StarTrackers

Radiator

WiFi

Power Cabling(& Data if needed)

Metering &Displacement System

(Mass ~ 50 kg)

The Arcus mission requirements are similar to those that have been pro-posed for the Constellation-X and IXO X-ray grating spectrometers. On WKH�,66��LVVXHV�RI�PDVV��SRZHU��DQG�GDWD�WUDQVPLVVLRQ�EHFRPH�PXFK�OHVV�GLIÀFXOW��%DVHG�RQ�WKH�1,&(5�GHVLJQ�VWXGLHV��ZH�H[SHFW�DW�OHDVW�����RE-VHUYLQJ�HIÀFLHQF\�GXULQJ�D���\HDU�EDVHOLQH�PLVVLRQ��ZKLFK�ZLOO�HQDEOH�XV�to complete all of the science planned for IXO.$UFXV�ZLOO�XVH�DQ�KLJK�75/�SUHFLVLRQ�RSWLFDO�EHQFK�VLPLODU�WR�WKDW�RI�NuSTAR. The bench carries with it a shroud for stray light control. A full-size prototype of this shroud-enclosed bench has undergone over 200 GHSOR\PHQW�F\FOHV�GXULQJ�JURXQG�WHVWLQJ��/LNH�1X67$5�DQG�$VWUR�+��D�PHWURORJ\�V\VWHP�LV�HPSOR\HG�WR�WUDFN���DQG�FRUUHFW�IRU���UHODWLYH�PRWLRQ�EHWZHHQ�WKH�RSWLFV�DQG�WKH�IRFDO�SODQH�GXH�WR�WKH�VOLJKWO\�ÁH[LEOH�EHQFK�Contamination from other activies on or around the ISS has been a con-FHUQ�IRU�;�UD\�RSWLFV��EXW�UHFHQW�VWXGLHV��H�J��6WHDJDOO�HW�DO��������-65����������VKRZ�WKDW�WKHVH�SUREOHPV�KDYH�ODUJHO\�DEDWHG��H[FHSW�GXULQJ�H[-WHUQDO�GRFNLQJ�RI�SD\ORDGV�DQG�VLPLODU�HYHQWV���7KH�ÀJXUH�DW�right shows Arcus in ob-VHUYLQJ�PRGH��mounted to the FRAM via a two-axis gim-bal system. The EOB system is completely con-tained within the circular ring beneath the op-tical layout.

Grating Arrays

To achieve the required 650 cm2�DUHD�DW�����NH9��Arcus uses at least 3 ‘petals’ (goal of 4) op-WLPDOO\�SDFNHG�ZLWK�VLO-LFRQ�SRUH�RSWLFV��632��with a ~5m focal length and off-plane grating modules (see right).

Each petal will have an individual focal plane GHWHFWRU��FRQVLVWLQJ�RI�D�6X]DNX�W\SH�EDFN�LOOXPLQDWHG�&&'�show in this diagram as a rectangle near the narrow end of each petal. The modular petal design leaves us substantial freedom to arrange the V\VWHP�WR�ÀW�ZLWKLQ�WKH�ISS and other mission re-quirements.

To maximize the low-en-HUJ\�WKURXJKSXW��$U-FXV�UHXVHV�ÀOWHUV�GHYHO-oped for Astro-H and the UW-Madision XQC VRXQGLQJ�URFNHW�SURJUDP�(shown at right).

IncomingLight

Star Tracker

Optics Assembly(incl. Gratings)

Deployable Boom

Detectors andControl Electronics

Internal MetrologySystem and light-rejecting“sock” (not shown)

Gimbals

FRAM Support Plate

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