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Ray-tracing simulation and in-orbit performance of the ASTRO-H hard x- ray telescope (HXT)

H. Matsumoto, H. Awaki, A. Furuzawa, M. Ishida, H. Kunieda, et al.

H. Matsumoto, H. Awaki, A. Furuzawa, M. Ishida, H. Kunieda, Y. Haba, T. Hayashi, R. Iizuka, K. Ishibashi, M. Itoh, T. Kosaka, Y. Maeda, I. Mitsuishi, T. Miyazawa, H. Mori, H. Nagano, Y. Namba, Y. Ogasaka, K. Ogi, T. Okajima, S. Sugita, Y. Suzuki, K. Tamura, Y. Tawara, K. Uesugi, S. Yamauchi, "Ray-tracing simulation and in-orbit performance of the ASTRO-H hard x-ray telescope (HXT)," Proc. SPIE 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, 990541 (19 July 2016); doi: 10.1117/12.2232135

Event: SPIE Astronomical Telescopes + Instrumentation, 2016, Edinburgh, United Kingdom

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tracing simulation and in H. Awaki Y. Tawara - , Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, edited by and Instrumentation 2016: Ultraviolet to Gamma Ray, Telescopes Space *a Figure 10%. Department of Technology, Nagoya University, Japan; University, Nagoya of Technology, Department of the ofASTRO k Ray Ehime University, Japan; University, Ehime Jan-Willem A. den Herder, Tadayuki Takahashi, Marshall Bautz, Proc. of SPIE Vol. 9905, 990541 Marshall Bautz, Proc. of SPIE Vol. Takahashi, Tadayuki A. den Herder, Jan-Willem b , Y. Namba

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The Hard X Hard X reflectors reflectcan hard X developed. measurements within encircled energy function and measure the half power diameter obtained Keywords: from the data are consistent with the ground A A ray

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2. RAY-TRACING SIMULATIONS A ray-tracing code is being developed by a Hitomi software team. Energy dependence of the half power diameter (HPD) and that of the effective area were simulated based on the ray-tracing code. These results were compared with HXT performances measured at the synchrotron facility, SPring-8 Beam Line 20B2, where we have built a general calibration system for X-ray telescopes2. Both the HPD (Figure 2) and effective area (Figure 3) are consistent with the ground measurements within 10%.

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o 20 40 60 80 o 20 40 60 80 Energy lkeNg Energy [keV] Figure 2. Simulated effective area (red) and that measured at Synchrotron Facility SPring-8 Beam Line 20B2 (black). The HXT1 data are shown in the left panel, while those of HXT2 are shown in the right panel.

comp2_hpdilps_twps_scl_full.qdp 1013b3,0818 comp2_hpdilps_twps_scl_fullcidp(150714a,3) 2.5 2.5 Reperiment Experiment Simulation Simulation 2 2 - I 15 HXT1 Pull telescope H)(72 full telescope .1 [ 1.1 IS rd 0.9 0.9 o 20 40 60 80 o 20 40 so Energy [keNg Energy [keV] Figure 3. Simulated half power diameter (red) and that measured at Synchrotron Facility SPring-8 Beam Line 20B2 (black). The HXT1 data are shown in the left panel, while those of HXT2 are shown in the right panel.

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3. IN-ORBIT PERFORMANCE Hitomi observed the pulsar wind nebula G21.5-0.9 from Mar. 23 to 25 in 2016. The effective exposure time was 105.1 ks. The X-ray images taken with HXT and HXI are shown in Figure 4. The images above 50 keV are statistically poor. Then we focus on the data below 50 keV in the following analysis.

5-80keV 5-10keV 10-20 keV

HXT1 20-30keV 30-50keV 50-80 keV

5-80keV 5-10keV 10-20 keV

HXT2 20-30keV 30-50keV 50-80 keV

Figure 4 X-ray images of G21.5-0.9 obtained with HXT and HXI in various energy ranges. The top panel shows the HXT1 images, while the bottom panel shows the HXT2 images.

The location of the center of these images was examined. The center portion of the images was projected to the X and Y axes, and the projection profiles were fitted with the Lorentz function plus a constant component. The peak positions of these images thus determined are shown in Figure 5. The error bars show the 1휎 confidence range. We see no significant change among the various energy ranges. Then we define the image-formation position of the HXT as that in the 5—80 keV band.

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HXT1 5-80keV- HXT2 5-80keV HXT1 5-10keV HXT2 5-10keV y HXT1 10-20keV -- HXT210-20keV 1218 HXT1 20-30keV - 1217 HXT2 20-30keV ' 1-1XT130-SOkeV HXT2 30-50keV

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1211 1212 1213 1214 1213 1214 1215 X(pix) X (pix) Figure 5. Peak positions of the images shown in Figure 4. The error bars show The error bars show the 1휎 confidence range. One pixel size corresponds to 1.77 arcsec.

The encircled-energy functions (EEF) around the image-formation point in various energy ranges are shown in Figure 6. The HPD estimated from the EEF is also in Table 1. Both the EEF and HPD show no strong dependence on X-ray energy.

0.8 0.8

W 0.6 W 0.6 W 0.4 HXT1 5-80 keV 0.4 HXT2 5-80 keV HXT1 5-10 keV - HXT2 5-10 keV - 0.2 HXT1 10-20 keV 0.2 HXT2 10-20 keV -- HXT1 20-30 keV -e-- HXT2 20-30 keV .-a-- HXT130-50 keV HXT2 30-50 keV 0 0 0 50 100 150 200 250 0 50 100 150 200 250 arcsec arcsec Figure 6. Encircled energy function of HXT1 (left) and HXT2 (right) in various energy ranges.

Table 1. Half power diameter in arcsec determined from the EEF shown in Figure 6. Energy Range HXT1 HXT2 5 – 80 keV 106.2 106.2 5 – 10keV 106.2 106.2 10 – 20 keV 102.6 102.6 20 – 30 keV 102.6 106.2 30 – 50 keV 102.6 102.6

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The in-orbit encircled energy functions are compared with those measured at SPring-8 in Figure 8; the encircled energy functions of HXT1 at 30 keV, 40 keV, and 50 keV were measured, while those of HXT2 were obtained at 20 keV, 30 keV, 40 keV and 50 keV. The in-orbit data are roughly consistent with those measured on ground, but for HXT2 in the 10-20keV band, we see a little discrepancy. The reason for this is not fully understood, but the mirror foils at large radii that work effectively for the 20 keV X-rays might suffer gravitational distortion in the ground measurements. In general the core of the in-orbit function is slightly wider than that of the flight data. Probably this is because the core is affected by an intrinsic spatial extension of G21.5-0.93.

1.2 1.2 HXT1 G21.5 -0.9 20 -30keV - HXT1 ground @ 30keV - 1

0.8 0.8 ¡sa0.6 W 0.6 W 410.4 0.4 0.2 HXT1 G215 -0.9 30 -50keV - 0.2 HXT1 ground @ 30keV - 0 HXT1 ground @ 40keV - ' HXT1 ground @ 50keV - o0 -0.20 50 100 150 200 250 50 100 150 200 250 arcsec arcsec

1.2 1.2 1.2

0.8 0.8 0.8

0.6 W 0.s W 0.6

0.4 0.4 0.4 HXT2 G21.5 -0.9 30 -50keV- HXT2 G21.5 -0.9 20 -30keV HXT2 ground @ 30keV - 0.2 0.2 -- 0.2 HXT2 G215 -0.9 10 -20keV -- HXT2 ground @ 20keV - HXT2 ground @ 40keV - HXT2 ground @ 20keV - HXT2 ground @ 30keV - HXT2 ground @ SOkeV - 50 100 150 200 250 00 50 100 150 200 250 0 0 50 100 150 200 250 arcsec arcsec arcsec Figure 7. In-orbit encircled energy functions are compared with those measured at the Synchrotron facility SPring-8.

The energy-spectra obtained from the region within 4 arcmin from the image-formation center are shown in Figure 8. The background spectra taken from the outer region are subtracted. The spectra are fitted with the best-fit model to the NuSTAR spectrum3 with free noralizations. The flux in the 15-50keV band obtained from the HXT+HXI spectra is 4.75e-11 erg s-1 cm2, which is 6% smaller than the NuSTAR value. This suggests that the offset angle of G21.5-0.9 from the optical axis is less than 1 arcmin.

5 10 20 50 Energy (keV) Figure 8. X-ray spectra of G21.5-0.9 obtained with HXT1 and HXI-1 (black) and HXT2 and HXI2 (red). The data are fitted with the best-fit model to the NuSTAR spectrum3 with free normalizations.

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REFERENCES

[1] Awaki, H., Kunieda, H., Ishida, M., Matsumoto, H. et al., “Hard x-ray telescopes to be onboard ASTRO-H”, Applied Optics, vol. 53, issue 32, p. 7664 (2014) [2] Ogasaka, Y., et al., “Characterization of a Hard X-ray Telescope at Synchrotron Facility SPring-8”, Japanese Journal of Applied Physics, Volume 47, Issue 7, pp. 5743 (2008). [3] Nynka, M. et al., “NuSTAR Study of Hard X-Ray Morphology and Spectroscopy of PWN G21.5-0.9”, The Astrophysical Journal, Volume 789, Issue 1, article id. 72, 12 pp. (2014).

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