DIOS:  Dark  baryon  exploring  mission  

Performance improvements and schedule Possibility of performance improvements Since cost cap of JAXA's small mission has been renewed and Epsilon rocket keeps improving, we look into the following additional capability for DIOS. 1. Larger X-ray telescope: extension of focal length to 1.2 m will give a few times larger are, making DIOS also suitable for point sources.

2. Fast repointing capability: Fast maneuver will enable observing X-ray afterglow of gamma-ray bursts after about 3 minutes of the burst onset. Absorption line spectroscopy of host galaxy gas and intervening WHIM against strong afterglow will give rich information on distant metals.

Other science from DIOS: The large field of view (50 arcmin) of DIOS will enable us to observe large-scale plasmas in many objects very efficiently. Fig. 8 shows gas dynamics which can be performed from DIOS. Fig. 8: Gas dynamics studied with DIOS. Gas motion of ~10 km s-1 will

be resolved from all categories of large-scale plasmas.

T.  Ohashi,  Y.  Ishisaki,  Y.  Ezoe  (Tokyo  Metropolitan  U)，Y.  Tawara  (Nagoya  U)，K.  Mitsuda,  N.  Yamasaki,  Y.  Takei  (ISAS/JAXA)，and  DIOS  working  group  

DIOS  satellite.  An  X-‐ray  telescope  and  a  dewar  is  placed  on  the  satellite  bus.  End  to  end  length  of  solar  paddle  is  about  10  m.  

Abstract Among the 3 components of the local universe (dark energy 73%、dark matter 23%、baryon 4%), major part of baryons, even though they are normal matter, remains unidentified. It is predicted that baryons mostly remain in the form of Warm-Hot Intergalactic Medium (WHIM) and distribute along large-scale structures. Since WHIM has a temperature around 106 K, containing heavy elements, observation of red-shifted emission lines with TES microcalorimeters will show us 3-dimensional distribution of WHIM. DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite, aiming for launch in 2020 by JAXA's Epsilon rocket, carrying 4-reflection X-ray telescope and TES microcalorimeters cooled by mechanical coolers. The grasp (SΩ) will be very large, and DIOS can study dynamics of hot intergalactic medium, galactic winds, supernova remnants and many other extended sources. We need to further develop the technologies of the ASTRO-H microcalorimeters and the cooling system. We also look into a possibility of improving the area of the telescope over baseline design of DIOS and fast repointing capability, which would bring additional science to DIOS.

DIOS  payload  design  ~  Thermal  and  mechanical  design  allowing  cooler  power  ~  

DIOS will inherit all the technologies developed for ASTRO-H SXS, but improvements are needed such as cryogen free operation. Difference between DIOS and ASTRO-H is listed in Table 3. Major developments needed for DIOS are reliable cooling, anti-vibration measures, multi input SQUID for readout, magnetic shield, multiplexing technique (time domain or frequency domain), and aperture design against heat input from large field of view. Fig. 5 shows the payload design. One X-ray telescope and a dewar are the main parts. Mass of the payload is about 300 kg, and the spacecraft mass is about 600 kg, in the capability of Epsilon launch. Intrinsic vibration frequency is over 10 Hz, meeting the requirement. Thermal design based on the ASTRO-H cooler performance shows the cooler power to be about 280 W, resulting in a total mission power to be about 380 W. Solar paddle has 4 panels on each side. Other issues are contamination control, pyrotechnic parts, thermal vacuum test of the whole system, which all requires study including the bus system design. Command operation will be once a week nominally and downlink contacts will be needed twice per day.

DIOS ASTRO-H TES calorimeters with SQUID readout 　− magnetic shield

Si thermistor with JFET readout

256−400 pixels 　− heat input from wirings 　− multiplexing 　− multi-layer wirings

36 pixels

Wide field (50') with short FL (70 cm) 　− Aperture opening angle ±30° 　− Radiation heat input

Narrow field (3') with long FL (5.6 m)

Fig. 5: Payload of DIOS consists of X-ray telescope and the dewar.

Table 3: Comparison of DIOS and ASTRO-H SXS

DIOS  mission  ~  Very  high  sensiRvity  within  the  framework  of  JAXA's  small  satellite    ~  

Science  of  dark  baryons   ~ Cosmic structure traced by WHIM ~ Baryons occupy about 4% of the energy density of the universe, but more than half of them remains unidentified. Numerical simulations predicts that baryons exist as WHIM with a few times 106 K, tracing the large-scale structure of the universe. WHIM should contain heavy elements injected by galactic winds in the period of galaxy formation. Its density is around 10-5 cm-3 (10-100 times the mean density in the universe), so continuum X-ray are unobservable due to strong foreground emission in our Galaxy. Superior energy resolution can revolve red-shifted oxygen lines, and not only the WHIM detection but study of its 3-dimensional structure to z ~ 0.3 will be performed. 　WHIM accumulates energy released by gravitational collapse in the processes of galaxy and cluster formations, as well as heavy elements. So WHIM study will show us the thermal and chemical evolution of the universe from different looking angle than the collapsed objects. DIOS, with its wide field microcalorimeters, has a unique capability suitable for the study of WHIM.

Expected results from DIOS ~ Structure of WHIM probed by OVII and OVIII lines ~

DIOS DIOS will reveal the large-scale structure of the universe in a clearer way. Lines emitted from Galactic hot gas and solar-wind charge exchange are about 100 times stronger than the WHIM lines, and we need to choose energy ranges which are relatively free from those liens. This gives us several windows in the redshift space. Simulation of DIOS observations is shown in Fig. 6, for a 5 deg × 5 deg region with 1 Msec per pointing and a total observing time of 2 yrs. This is for a redshift range of 0.2 ± 0.02. Left panel shows the whole gas, and right one shows a map based on a simultaneous detection of OVII and OVIII lines over 5σ. Large-scale filaments can be seen fairly well (Takei et al. 2011, ApJ 734, 91).

Galaxies  (~104K)  Dark  maWer  

Fig.  1  (right)  Large-‐scale  structure  predicted  by  numerical  simulaRon.  Upper  leZ  panel  shows  the  dark  maWer  structure.  Galaxies  and  clusters  show  only  the  main  part,  but  WHIM  will  reveal  the  full  structures.  

Fig.  2  (below)  Pie  chart  of  baryon  consRtuents.  About  40%  is  missing,  and  even  WHIM  part  has  quite  large  uncertainty.

Cluster  gas  (107K)  Warm-‐hot  IGM  (105-‐107K)  

Fig.  3:  DIOS  payload  system

Mass total ~  400  kg  

payload ~  200  kg  

Size launch 1.2×1.45×1.4  m  

in  orbit 5.9×1.45×1.4  m  

Agtude control 3-‐axix

accuracy ≦30  arcsec

Power total 500  W  

payload >300  W  

EffecRve  Area  200  cm2        (>  100  cm2)      

F.  o.  v   50'  diameter  

SΩ

~  100  cm2deg2  (0.6  keV)  

Angular  resol.   3'  (16  x  16  pix  or  more)  

Energy  resol.   2  eV  (FWHM)  

Energy  range   0.3  –  1.5  keV  

Mission  life   >  1  yr  (goal  5  yr)   Fig.  4:  Grasp  (SΩ)  against  energy  resoluRon  for  missions

Table  1:  DIOS  spacecraZ

Table  2:  DIOS  instruments

Fig. 6: Gas structure in a redshift range z = 0.2 ± 0.02. Left panel shows the whole gas, and right panel shows DIOS observation of OVII and OVIII lines simultaneously over 5σ.

DIOS  2Ms

Fig. 7: WHIM density against surface brightness. Limit of 2 Ms observation with DIOS is indicated.

Fig. 9: Schedule of DIOS for a launch in 2020.

図 2: DIOS観測装置 (FXT+XSA)のシステム構成。

同一口径、同一入射角の場合でも、焦点距離を 2回反射鏡の約半分にすることができる。焦点距離が0.7 mであれば、10 mm程度の検出器で 1度の視野を見込むことができる。また、DIOSは伸展機構を持たない小型衛星であることからも、こうしたコンパクトな光学系が望ましい。

FXTの製作方法としては、最適設計を行い、「あすか」、「すざく」で実績のあるレプリカフォイルミラーの積層を考える。光線追跡法により、有効面積、視野、角度分解能等の性能を評価した。設計パラメータを表 4にまとめる。口径 60 cm, 焦点距離 70 cmの望遠鏡と 12 mm × 12 mmの検出器を組み合わせた場合の有効面積は、C(50 Å) + Ni(50 Å) + Pt(1000 Å)の複合鏡の場合、0.6 keVで500 cm2 以上であり、MgのK輝線を含む 1.5 keV程度までのエネルギーを観測することができる。視野は 0.97 deg2に相当し、端へ向かっての反射効率の劣化を考慮しても SΩ > 250 cm2deg2である。検出器側の検出効率が 50%程度であれば、SΩ > 100 cm2deg2を確保できる。また、質量は表 5 に示すように 24kgと軽量である。

FXTの製作では、基本的には「すざく」、「Astro-H」等の 2回反射Ｘ線望遠鏡の要素技術をすべて利用することができる。ガラスマンドレルからのレプリカミラー方式を基本とし、マンドレルを円筒から円錐にするなどの工夫で短焦点でも優れた撮像性能を実現する。CAD図と、実際に製作したquadrantのハウジングを図 3に示す。quadrantに一部の反射板をとりつけた望遠鏡に対して、Ｘ線ビームテストまで行い、角分解能 5分角 (HPD)を確認した、今後は 3分角を目標に各分解能の改善を図るとともに、総数 2728枚に及ぶ要素ミラーの量産体制の確立を目指す。

5

International collaboration Fig. 9 shows schedule for a launch in 2020. The hardware development is in progress, but international collaboration is important to meet this schedule. TES calorimeters with over 100 pixels will be developed together with US and Japan (with possible European support). Micro-X rocket payload will be the baseline for the DIOS instrument, including its readout system and cooling with ADR. There is a consortium comprising Japan, US and European members, and it has proposed several missions aiming for the dark baryon study. This group is expected to work together for DIOS including effort of obtaining national support.

DIOS (Diffuse Intergalactic Oxygen Surveyor)

DIOS (Diffuse Intergalactic Oxygen Surveyor)

1  m

DIOS

Fig. 3 shows a schematic payload design, consisting of 4-reflection telescope, TES microcalorimeters and cooling system. Life is determined by the mechanical cooler function. The cooling is performed by mechanical coolers of the same design as for ASTRO-H combined with adiabatic demagnetization refrigerators. The radiator at about 300 K exhausts the heat. Main parameters of the satellite are listed in Table 1, and those of instruments are shown in Table 2. The satellite will be 3-axis controlled and can point to desired direction with attitude measured by star trackers. The field of view is about 50 arcmin and the image is take by a TES array of 256 to 400 pixels. The grasp is about 150 cm2deg2, which is almost the largest in all X-ray missions and close to the level of Athena's X-IFU. The 4 reflection limits the energy range up to about 2 keV, but Fe-L and Si lines will enable us to study wide range of temperatures for clusters and SNRs.

Pointing of 2 Ms probes WHIM spatial density dN/dz ~ 1. Observing 20 square degrees with Δz = 0.02, 100- 200 WHIM clouds will be detected and about 30% of dark baryons probed.

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Launch

2016 2017 2018 2019 2020 2021 202320222015CY

SpacecraZ

Payload  

   Coolers      TES  

   Electronics  

   Telescope

WHIM  survey GO      

Test  of  whole  payload

Proposal-‐selecRon

1081

10

100

1000

10000

v  (km/s)

SpaRal  scale  (pc)

100 104102 106

SNR  shocks

GalacRc  winds

AGN  jets

WHIM  Filaments

Cooling  flows

Evolved  SNR

Cluster  merger

XMM

Chandra

Suzaku--XIS

ATHENA--X4IFU

ASTRO4H--SXS

DIOS

1000

100

10

1

0.10.1 1 10 100

Energy-ResoluCon-(eV)

SΩ-(cm

2 -deg

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