Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Silicon Optics for Wide Field X-ray Imaging Dick Willingale University of Leicester Macelo Ackermann and Max Collon Cosine Research B.V. SPIE Optics for EUV, X-Ray, and Gamma-Ray Astronomy VI San Diego 2013 August 27 th – 29 th

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Scientific Motivation Soft X-ray surveys –High angular resolution – Large sky area – Faint sources – AGN, Clusters of Galaxies… Soft X-ray transient astronomy – Good angular resolution – All sky – Short lived phenomena – GRBs, Novae… 2

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Si pore optics – XEUS to Athena 3 Focal length F=12m Rib spacing 0.83 mm Radial width Δr=0.605 mm Axial length 4.F.Δr/R Si pore module – Cosine Research Module layout – Owl design SPO originally designed for narrow field imaging with large collecting area

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Manufacture of SPO modules 4 ESA - Cosine Research

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Wide field imaging with SPO How can we modify the baseline SPO design to achieve wide field X-ray imaging? SPO are potentially good for wide field because the reflecting surfaces have a small axial length… 5

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Vignetting In-plane vignetting –Radial pore size d (fixed) –Length of pores L –Drops to zero at θ≈d/2L 6 Out-of-plane vignetting –Rib spacing d rib –Length of pores L –Drops to zero at θ≈d rib /2L Ray tracing of a single module

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Field of view vs. d rib for Athena+ 7 d rib 1, 2, 3, 4, 5 mm FOV at half on-axis area 1 keV Ray tracing full aperture

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Wide field Si pore optics – Athena+ 8 Focal length F=12m Wide rib spacing d rib 3 mm Radial width d=0.605 mm 800 – 1000 modules The optical design of the Athena+ mirror Willingale, Pareschi, Christensen, den Herder arXiv:

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 FOV, Photon Energy, Grasp – d rib 3mm 9

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Angular resolution off-axis Wolter I –principal plane (join plane) flat 10 Wolter-Schwartzschild (W-S) Obeys Abbe sine condition – principal plane spherical radius curvature F Polynomial figure not useful – modules small axial Length

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Angular resolution off-axis Figure and alignment errors – 5 arc sec HEW on-axis Axial curvature – approximate Wolter I or W-S Conical approximation ~5 arc sec HEW for F=12m W-S with axial curvature – 6.5 arc sec HEW average over 50 arc mins diameter FOV 11

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Deep X-ray Transient Imaging Require: FOV ~20 by 20 degrees or much larger Continuous coverage ~ 500 square degrees or much more Collecting area >> few cm 2 Sensitivity to transient sources - Δt 1 second - 1 day A true imaging optic to give maximum sensitivity 12 Wolter I: FOV diameter limited to ~twice grazing angle - only ~2 o Could use a fly’s-eye of small Wolter Is but very inefficient 2 in-plane reflections - lateral inversion in the image plane Solution: Square pore or Kirkpatrick-Baez geometry

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August K-B Stack – Schmidt Geometry

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 K-B Si Pore module Module shown is a Wolter I conical approximation prototype Can easily be constructed in the Kirkpatrick Baez geometry 14 square aperture, side length S number of plates N p =S/P P=760 μm T=150 μm D=610 μm open fraction front+rear 64% Wolter I Si pore module – Cosine Research No plate curvature required Plates wedged so point at common centre of curvature All stacks are identical Rib period must match wafer thickness No lateral inversion in image plane

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Packing of K-B stacks into an aperture 15 Focal length 5 m (needs to be > ~2.5 m for SPO manufacture) Collecting area ~100 cm 2, angular resolution ~20 arc seconds Using N identical K-B SPO modules For wide field K-B modules aligned on spherical surface R=2F – large FOV If co-aligned on plane surface get N narrow field foci – large area 4 modules can form a small narrow field instrument

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Wide field K-B stacks Grazing angle 1 degrees –slot width mm –axial slot length 35 mm FOV 20 degrees diameter Collecting area ~110 cm 2 at 1 keV (~constant over FOV) HEW ~22 arc seconds (constant over FOV) Grasp 3.46 m 2 deg 2 at 1 keV Focusing gain ~13300 Area at 13 cm 2 at 6.5 keV HEW limited by flat plates – can be improved using axially curved plates 16 Vignetting at 1 keV Area vs. energy

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Summary ~800 Si pore optics Wolter/W-S modules with wide rib spacing (>3 mm) can provide grasp ~same as WFXT ~0.5 m 2 deg 2 at 1 keV W-S spherical join plane and approximate axial curvature with 5 arc sec HEW on-axis will give average HEW of 6.5 arc seconds over FOV 50 arc mins in diameter Si pore K-B stacks in Schmidt geometry provide –20 degree diameter FOV – ~300 deg 2 –with ~100 cm 2 at 1 keV and HEW of ~20 arc secs –Grasp is ~10x WFXT – focusing gain – Deep wide field imaging – faint transient imaging Identical Si pore K-B stacks can also provide –Large area on narrow field – co-aligned over plane surface – N foci –Multiple small narrow field telescopes e.g. X-Nav telescopes 17

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 The End 18

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 WFXT approach Proposal to NASA – P.I. S. Murray Optics – INAF/Brera – G. Pareschi Thin shell Wolter I with polynominal figure 19

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Wide field Si pore optics Original pore geometry – grasp 0.19 m 2 deg 2 at 1 keV Wide field pore geometry – grasp 0.34 m 2 deg 2 at 1 keV HEW limited by conical approximation –Can be improved by including axial curvature Using Ir coating – a C overcoat would increase the low energy area 20

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Soft X-ray large sky area surveys 21 Looking for 5 arc sec over 1 degree FOV with collecting area ~ 4000 cm 2

Silicon Optics for Wide Field X-ray Imaging Dick Willingale et al. – SPIE August 2013 Soft X-ray Transient Astronomy ? Line: Lobster module F=300 mm Red points: Swift BAT short GRBs Black points: Swift BAT long GRBs Green points: Swift XRT GRB afterglows Looking for 1 arc min over 30 degree FOV with collecting area ~ 10 cm 2