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GEO-X : Geospace X-ray imagerYuichiro Ezoe1, Yoshizumi Miyoshi2, Satoshi Kasahara3,

Hiroshi Hasegawa3, Tomoki Kimura3, Takaya Ohashi1, Yoshitaka Ishisaki1, Ikuyuki Mitsuishi1,2,Ryuichi Fujimoto4, Kazuhisa Mitsuda1, Atsushi Noda4, Kunitoshi Nishijo4, the GEO-X team

1 Tokyo Metropolitan Uni., 2 Nagoya Uni., 3 ISAS/JAXA, 4 MDSG/JAXA, E-mail : ezoe@tmu.ac.jp

1. GEO-X mission

2. Science goals & requirements

3. Science PayloadRecent observations with Earth-orbiting X-ray astronomy satellites revealed time-variable X-ray emission from Earth’s magnetosphere (m-sphere) via Charge eXchange (CX) between solar wind and exospheric neutrals.

Our science goal is visualization of m-spheric boundaries (cusp, sheath, LLBL etc..) in soft X-rays (<~1.5 keV). Requirements to meet this science goal are defined as follows.

Figure 2 – Concept of the JUXTA instrument and new technologies for the telescope (Ezoe et al., 2012, Opt. Let., 37, 779) and detector (Strueder et al., 2010, SPIE, 7732, 7732I).

Table 1 – Instrument parameters.

Figure 1 – Science objectives of JUXTA (see Ezoe et al., 2013, Adv. Space Res., 51, 1605 and references therein).

Figure 3 – JUXTA for future exploration missions and micro/small satellites.

Item Value Telescope Energy range Spatial resolution FOV Effective area Focal length

0.3-2 keV <5 arcmin 4 deg φ 3 cm2 25 cm

Detector Energy resolution Array size Pixel size

<100 eV FWHM ~2 cm x 2 cm ~200 µm x 200 µm

Instrument Mass Size Power Data rate

~10 kg ~25 cm x 25 cm x 25 cm ~10 W ~10 kbps

Item Requirements (at 60 RE) Comment

Energy band 0.3 - 2 keV・C, N, O, Fe, Ne, Mg emission lines (<~ 1.5 keV)・Estimate NXB by impacts of ions using X-ray photons above 1 keV

Spatial reso. <0.1 RE (<6 arcmin) • Resolve fine structures of cusp and sheath

Energy reso. <100 eV @ OVII Kα 0.6 keV • Resolve C, N, O, Fe, Ne Mg emission lines

Time cadence<1 hr (>~ 20 cm2 deg2 @ OVII Kα 0.6 keV)

・Detect changes of m-sphere in size and shape・Expected X-ray flux for a large magnetic storm event ~0.1 cps @ OVII Kα

FOV > 5 RE x 5 RE (5° x 5°) ・Grasp cusp and sheath at the same time

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䐠 Perigee䛻䛶ǻ91䠖770[m/sec]䜢ຍ䛘䛶Apogee㧗ᗘ䜢᭶㧗ᗘ䛻ୖ䛢䜛䠄200km×378,370km䠅

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䐢 Perigee䛻䛶ǻ92䠖134[m/sec] 䛷ῶ㏿䛧䛶239,000[䡇䡉]䛾㌶㐨䛻ධ䜜䜛

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ᆅ⌫ ᭶

4

Sun

Magnetic Field

Solar Wind

Exosphere

EarthO7+

H

O6+

e- X-ray

The X-ray intensity is “expected” to be strong at m-spheric boundaries such as magnetosheath and cusps.

We have begun concept study of a new mission GEO-X, aiming at “imaging” of Earth’s m-sphere in X-rays for the first time. Our initial study confirms that such a mission is achievable in JAXA’s small scientific satellite program.

To this end, we plan to have a 2x2 array of compact X-ray telescope units (XTUs).

cuspsheath

9

SDS-4 Spacecraft Overview

�

50kg class�

zero momentum 3-axis stabilized�

Sun oriented �

SSO altitude approx. 677km�

Piggyback payload of H-IIA LV ( FY2011 )

Weight approx. 48kgSize approx. 500�500�450 mm

Power approx. 120 WAttitude Control Three-axis Sun-oriented

Communication

S-band1 Mbps (mission downlink)

16 kbps (downlink)4 kbps (uplink)

Orbit SSO, altitude approx. 677km

Each XTU is composed of an X-ray telescope and a detector. We are currently developing a new X-ray telescope, called MEMS X-ray optics for GEO-X as well as X-ray astronomy missions. We have constructed a Wolter type-I optic optimized for soft X-rays.

Al Kα 1.49 keV

A MEMS X-ray optic is made from a few hundreds µm thick Si wafers with metal coating. It is ultra light in weight (x >40 lighter than past X-ray telescopes).

Johannes Treis MPI Halbleiterlabor 17

Prototype Macropixel devices

Demonstrator

Z pixel 500 x 500 µm²

Z format 64 x 64 pixels

3.2 x 3.2 cm²

Z frametime 450 Psec (ASTEROID)

Z temperature -80 … -90 °C

Z representative scalable results

<Expected performances>Pixel size：300 μm squareArray：64 x 64Size：1.92 cm x 1.92 cmFrame time：1 msTemperature ：<~-40 deg CE reso.：<100 eV @ 0.6 keVPower & weight : 10 W & 3.5 kg (incl. readout electronics)

<Expected performances>Diameter : 100 mmFocal length : 250 mmFOV : 4° in diameterOn-axis area : 4 cm2 @ 0.6 keVGrasp (SΩ) : 16 cm2 deg2 @ 0.6 keVWeight : 5 kg (mirrors are only 4 g)

Majewski+13

mid 2010’s early 2020’s

Solar Sail

JMO

Johannes Treis MPI Halbleiterlabor 17

Prototype Macropixel devices

Demonstrator

Z pixel 500 x 500 µm²

Z format 64 x 64 pixels

3.2 x 3.2 cm²

Z frametime 450 Psec (ASTEROID)

Z temperature -80 … -90 °C

Z representative scalable results

Earth’s m-sphere

late 2020’s

Technology development

Jupiter, Mars, Moon

GEO-X

9

SDS-4 Spacecraft Overview

�

50kg class�

zero momentum 3-axis stabilized�

Sun oriented �

SSO altitude approx. 677km�

Piggyback payload of H-IIA LV ( FY2011 )

Weight approx. 48kgSize approx. 500�500�450 mm

Power approx. 120 WAttitude Control Three-axis Sun-oriented

Communication

S-band1 Mbps (mission downlink)

16 kbps (downlink)4 kbps (uplink)

Orbit SSO, altitude approx. 677km

Several targets for future observations

1: global imaging of magnetosphere

- Field of view: 20 Re x 20 Re - View points: from side: visualization of the cusp from top : visualization of KHI at the flank

- Observations for understanding solar wind – magnetosphere interactions.

Z (G

SM)

X (GSM)

- Lunar orbit should be a good platform to observe global distributions.

Miyoshi+13

②

<Resources per XTU>Mass : 10 kgPower : 10 WSize : 30 cm cubicFOV : 4° x 4°

>

FWHM 4 arcmin

独 PNsensor, MPE が開発

Global&distribu7on&of&So:;Xray�Estimation of X-ray emission

������X-ray power density 3 1( )sw HP n g n eVcm sα − −=

��geocoronal hydrogen density ( )3

10 Re25Hn r! "

= # $% &

��solar wind density swn

��total relative speed 2 2sw thermalg u v< >= +

From MHD model

From geocoronal model spherically symmetric

��abundance of high-charge state population Assumption: O7+ is 0.1 % of H+

22 1 1

1

1( )4

r

xrayr

B eVcm s str P drπ

− − − = ∫

Team GEO-X�

Global&distribu7on&of&So:;Xray�Estimation of X-ray emission

������X-ray power density 3 1( )sw HP n g n eVcm sα − −=

��geocoronal hydrogen density ( )3

10 Re25Hn r! "

= # $% &

��solar wind density swn

��total relative speed 2 2sw thermalg u v< >= +

From MHD model

From geocoronal model spherically symmetric

��abundance of high-charge state population Assumption: O7+ is 0.1 % of H+

22 1 1

1

1( )4

r

xrayr

B eVcm s str P drπ

− − − = ∫

Team GEO-X�

the subsolar region. Clearly, a suitably instrumented space-craft should be able to detect the cusps in soft X rays.

3.2. X-Ray Observations From Outside theMagnetosheath

[22] Robertson and Cravens [2003] created images ofSWCX X-ray emission as would be seen from an observa-tion point 50 RE removed from Earth. The observation pointwas along the y axis perpendicular to the x-z plane, wherethe x axis is directed from the Earth to the Sun. Averagesolar wind conditions were used. The cusps were notincluded in this earlier study. We have now created a similarimage, but for the 31 March 2001 event and including thecusps. Figure 3 shows predicted X-ray production rates inthe GSM x-z plane (y = 0). Earth is located at the center ofthe image. The axes are in units of D, which is the subsolardistance to the magnetopause (6 RE in our case). Theresolution is 101 ! 101 pixels, which is sufficiently highfor the cusps to be evident.[23] The cusps do not extend all the way to Earth because

in our current simulations it is impossible to identify purely

solar wind plasma close to Earth. Similar to modeledobservations made by a hypothetical X-ray detector onIMAGE, the production rate is clearly at a maximum inthe cusp region, with a secondary maximum in the subsolarregion. In the flanks and tail region, where the solar winddensity is much lower, the production rates are significantlylower too.[24] Integration along each of the 101 ! 101 lines of sight

produces the image of SWCX soft X-ray emission (seeFigure 4, left side). The largest X-ray intensities are for thecusps, followed by a secondary maximum in the subsolarregion (40% less than in the cusps). Because the lines ofsight intersect the flanks, the bowshock and the magneto-pause are more diffuse, but can still be seen clearly. Themaximum subsolar X-ray intensity is twice the intensity thatwould be seen from inside the magnetosheath due to thegeometrical effects.[25] Robertson and Cravens [2003] showed images from

‘‘the outside’’ for a subsolar magnetopause distance of9.5 RE (see right side of Figure 4). The upstream solarwind density for that paper was 7 cm"3 and the speed was400 km/s. The maximum intensity obtained for thoseconditions was about 8 keV cm"2 s"1 sr"1, which was inthe subsolar region. On the other hand the maximumpredicted intensity for the subsolar region for the31 March 2001 conditions is about 160 keV cm"2 s"1 sr"1,which is a factor of 20 greater than the maximum valuesRobertson and Cravens [2003] obtained for average solarwind conditions. This clearly shows the time variability ofX-ray emissions produced by the SWCX mechanism as wellas the highly nonlinear response of the intensity as themagnetopause moves closer to the Earth. This behavior issimilar to that actually observed in the low-energy neutralatom data and simulations.[26] Charge transfer between solar wind alpha particles

and neutral hydrogen produces He+ 30.4 nm emission[Gruntman, 2001]. This process is essentially the same asthe soft X-ray process except that the He++ charge exchangecross sections are more velocity dependent and somewhatsmaller than the heavier ion cross sections. The intensitymaps in Figures 2 and 4 can easily be converted to

Figure 3. X-ray production plot in the GSM x-z plane.Earth is at (0,0). Axes are in distance to the subsolarmagnetopause (D).

Figure 4. X-ray intensities for the 31 March 2001 event, as observed from the GSM y axis 50 RE

removed from Earth (left). Units are in D, distance to the subsolar magnetopause. The right side wasmodeled by Robertson and Cravens [2003] for average solar wind conditions. Note that the color scalesof the two panels differ. To convert this map to 30.4 nm emission (photons/cm2/s/sr), multiply the X-rayintensities by 2.5 (see text for details).

A12105 ROBERTSON ET AL.: MAGNETOSHEATH X-RAY EMISSIONS

5 of 8

A12105

Expected X-rays as seen at GSE Y = 60 RE (Robertson+06)

Launch : JAXA’s Epsilon rocketSpacecraft : 330 kg (wet), 235 kg (dry)Science payload : 40 kg, 40 WAttitude : 3-axis stabilized (accuracy 1 arcmin/min)Data rate : ~30 kbps (mainly science data)

Earth MoonLunar swingby

Launch from USC (Uchinoura Space Center)

Orbit : two candidates(a) HEO, (b) Earth-Moon L1

Figure 2. Process flow of MEMS X-ray optics.

Table 1. Development items reported in this paper and their correspondence to each process step shown in figure 2.

process step 1 2 3 4 5§3. single-stage optics

! ! !

§4. coating of a heavy metal! ! !

§5. Wolter type-I optics! ! !

This method hold many advantages over the traditional mirrors and the other micro pore optics. The maturedphotolithography technology allows accurately-arranged micro pores with a width of a few tens µm. High aspectratio more than 10 is possible. The sti!ness of silicon and nickel micro structures enables a large open area ratiomore than 10 %. Consequently, the mass to area ratio shown in figure 1 can be extremely small, "1 kg for 1000cm2. Also, a large, more than 4 inch in diameter, single-piece optic can be fabricated by use of a commerciallyavailable large wafer. A short focal length optic of <1 m is possible without degradation of angular resolutiondue to the negligible conical approximation. Assuming that the side walls of the micro pores are flat and themirror arrangement is perfect, a theoretical limit on the angular resolution arises from X-ray di!raction within anarrow micro pore. If the pore width d is 20 µm and the X-ray wavelength ! is 1.24 nm (1 keV), the theoreticallimit is represented as " !/d "13 arcsec. Our final goal is this X-ray di!raction limited micro pore X-ray optics.

We started our development of this novel method with miniature optics (7.5#7.5 mm2) made of silicon and

X-ray

100 mm

20 µm-width curvilinear pores

Assembly of Wolter type-I

optic

2013 Oct

DepFET sensors developed by MPE are low noise, high frame rate, and extremely radiation hard, ideal for astronomy and planetary missions. We plan to use this detector for GEO-X.

Ezoe+12

Ogawa+14

32 mm500 µm pixel

Calibration of the DEPFET Detectors for the MIXS Instrument on BepiColombo 9

. ........

(a) (c)

(b) (d)

Fig. 2 Spectroscopic Performance. (a) Spectra of single events for all three detector modulesrecorded at a beam energy of 3314 eV. Peak and escape peak are clearly visible. The energyresolution is 103 eV ! FWHM ! 104 eV for single events and 107 eV ! FWHM ! 108 eVfor all valid events. (b) Spectra of single events for all three detector modules recorded at abeam energy of 500 eV. The energy resolution is 64 eV ! FWHM ! 67 eV for single eventsand 66 eV ! FWHM ! 69 eV for all valid events. (c) Energy resolution FWHM (singleevents) vs. photon energy for all three modules over the full energy range. As a referencethe theoretical Fano limit is shown as a dashed line. For completeness, also the result fromthe reference measurement with an 55Fe source which was recorded during the spectroscopicmeasurements before the transfer to BESSY is indicated. (d) Energy resolution FWHM forsingle events and all valid events vs. photon energy for module DPA F10.

the theoretical Fano limit, which is shown in the graph as a dashed line. At anenergy of 1820 eV, just below the silicon absorption edge (1839 eV), a dip inthe data is visible. As photons of this energy have a significantly larger pen-etration depth compared to photons at an energy of 1860 eV, just above theSi-K absorption edge, signal charge produced by these photons is significantlyless a!ected by e!ects of charge recombination in the vicinity of the dead layerat the entrance window region, hence the FWHM is narrower. For the moduleDPA F09 additional flat field measurements were done to study the propertiesclose to the Al-K edge (1560 eV) and the same e!ect - but to a much lower ex-tend - was shown. This is caused by the thin Al layer on the entrance windowside of the detector chip, which serves as an intrinsic light filter. In additionto the data points derived from the calibration measurements at BESSY-II,the energy resolution measured with an 55Fe source (Mn-K!: 5.9 keV) sev-

O Kα 0.5 keV

A typical X-ray flux in large CME and geomagnetic storm events (Dst < -100 nT) is ~30 and ~10 ph/cm2/s/str @ 0.6 keV for cusp and sheath. With one XTU, this promises S/N = 10 in ~1 ks and ~3 ks exposure times, satisfying the required time cadence (<1 hr).In early 2020’s, we expect that such events will occur ~5-10 per year.

4. Future prospectsWe plan to propose GEO-X for a future call of JAXA’s small science satellites. The earliest opportunity will be early 2020’s, corresponding to the next solar maximum phase. We envision that the XTU will be used in various future exploration missions.