X-ray Telescope (XRT)
1. Instrumental Requirements for XRT
The instrumental requirements for the Solar-B/X-ray telescope(XRT) are:ooooo

In order to isolate coronal structures that correspond to magnetic elements seen in the
optical telescope, the pixel size must be of order 1 arcsec.
Because coronal events are often global, XRT must provide full Sun imaging.
In comparison to Yohkoh/SXT, the low T response must be increased.
Because both hot and cool features need to be observed, the telescope should cover abroad range of temperatures.
The XRT temperature coverage should include that of the EIS.

These requirements can be accomplished with an optimized Wolter I grazing-incidence telescope
similar to that used on Yohkoh, although with certain modifications, plus a large format backilluminated CCD detector and appropriate entrance aperture and focal plane filters.

2. Optics
XRT has two optical systems. One is for X-ray and the other is for visible light (G-band). Theoptics is similar to Yohkoh/SXT and these optical systems make X-ray and G-band images onone CCD.
X-RayOptimized Wolter-I Grazing Incidence Optics
Focal Length

2708 mm

Aperture Size

> 340 mm

Band Width2 − 200 Å

Effective Area

> 3.0cm2 @ 0.56 keV & 1 keV

Field of View

>30 arcmin

XRT Optics (XRT-T)

Visible Light
Focal Length

2708 mm

Wavelength4305 Å

Field of View

>30 arcmin

Reference: XRT ICD (ICD Requirements)

3. X-ray Analysis Filters
XRT has two filter wheels for X-ray analysis filters and a G-band filter. These filter wheels have intotal 12 positions (6 position in each filter wheel). 9 positions are used for X-ray analysis filters.
The X-ray analysis filters (see the following table and figures) shall provide the capability oftemperature analysis over the range 6.1 < log T < 7.5.

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Design of X-ray Analysis Filters
Name

Metal

Metal Thickness

Substrate

Substrate Thickness

Thin-Al/Mesh

Al1600 Å

Mesh

N/A

Thin-Al/PolyAl

1250 Å

Polyimide

2500 Å

Thin-Be

Be

9 µm

Mesh

N/A

Med-Be

Be

30 µm

N/A

N/A

Thick-Be

Be

1 mm

N/A

N/A

Thick-Al

Al25 µm

N/A

N/A

Med-AlAl

12.5 µm

N/A

N/A

Ti/PolyTi

2300 ÅPolyimide

2500 ÅC/PolyC

4800 Å

Polyimide

2500 ÅThese temperature response functions include the properties of the entrance filter, the effective areaof the X-ray mirror, and QE of the CCD.

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4. Camera (CCD)
In order to provide a high-resolution soft X-ray image with low noise and large dynamic range, thedata acquisition system for XRT uses a single 2k × 2k pixel CCD array. The CCD will be operated
under –43 °C on the orbit.
CCD Type

2k × 2k back-illuminated CCD (E2C/CCD 42-40)

Pixel Size

13.5 × 13.5 µm(Correspond to 1 arcsec × 1 arcsec)
1 × 1, 2 × 2, 4 × 4, 8 × 8

Pixel Binning Mode
2Dark Current
CTE*

0.4 nA/cm (0.1 electrons/sec/pixel @ -65 °C)
Parallel >0.999996, Serial > 0.999999 (–93 < T (°C) < –50)

QE* (X-ray/EUV)

0.93@13Å, 0.61@45Å, 0.46@116Å, 0.56@304Å

QE (Visible Light)

0.44@4000Å, 0.66@5000Å

Full-well Capacity

2.0 × 105 electrons*The values of CTE and QE (X-ray/EUV) are preliminary results from the CCD calibration test at NAOJ.

XRT can take partial frame images. The sizes of partial frame images are 64,128, 192, 256, 384,512, 768, 1024, 1536, and 2048 pixels. We can select not only square but also rectangular areas
for the shape of partial frame images (ex. 1024 × 256, 256 × 512). The size of 64 pixels is,however, used only for the square images (64 × 64).
XRT has a focus adjustment mechanism. The range of focus adjustment is ± 1 mm. We can use
the mechanism for canceling the focus shift by the launch environments.

5. Mission Data Processor (MDP)The Mission Data Processor (MDP) of Solar-B not only handles the data from XRT/FPP/EIS, butalso controls XRT using observation tables and the results of image analysis on MDP. Theobservation tables and the parameters for the image analysis are uploaded from the groundstation.
<MDP Functions for XRT>
oObservation controlled by observation tables.

¾

Compile exposure parameters based on the observation table and send thesecommands to XRT.

¾

Highest time resolution of XRT is 2 sec.

¾

Change the observation table for flares, automatically.

oAutomatic Exposure Control (AEC)¾MDP achieves the proper exposure time by analyzing intensity distribution of observed
X-ray images.

¾MDP also selects the proper X-ray analysis filter (Default or Thick filter).

¾

AEC can apply to an image that is smaller than 256 k pixels (= 512 × 512 image).

oAutomatic Region Selector (ARS)¾

MDP selects the region suitable for observation by onboard image analysis.

¾ARS have two modes.

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¾

GLOBAL search: Select the brightest region in the field of view.

LOACL search: Track 3 specific regions

MDP uses ARS patrol images for the ARS function. The time resolution of ARS depends
on the time resolution of ARS patrol images. The baseline of ARS time resolution is 1.5hour (~one orbit).

oFlare Detection (FLD)¾

MDP can detect the occurrence of a flare using flare patrol images taken by XRT.

¾Detection by intensity increase compared with previous running-averaged patrol image.

¾When MDP detects the occurrence of a flare, MDP changes the observation table forflare observation and informs the flare to SOT and EIS.

¾The function also detects radiation belts (SAA and HLZ).

oPre-Flare Buffer¾Observers can select the use of the special buffer for pre-flare observations byobserving tables.

¾If MDP detects the occurrence of a flare and XRT is observing the flare site before theflare, MDP keeps the data in the pre-flare buffer until the downlink. If MDP does notdetect a flare, MDP writes the data over the previous data on the pre-flare buffer.

¾The size of the pre-flare buffer is total 5.5 Mbytes.

oImage Compression¾

MDP can compress the image data using JPEG or DPCM method.

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