Wide X-ray Field of View

Transcription

1 NAOC Beijing June 25 th 2013 Wide X-ray Field of View Dick Willingale University of Leicester

2 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 X-ray optics focusing highest signal-to-noise 2

3 X-ray Optics Geometry 3 Options Wolter Type I XMM-Newton, Chandra, Swift Angel - Square Pore Lobster Eye Kirkpatrick-Baez - Schmidt Geometry Always 2 grazing incidence reflections to focus 3

4 Soft X-ray large sky area surveys Want 5 arc sec over 1 degree FOV with collecting area ~ 1 m 2 4

5 WFXT approach Proposal to NASA P.I. S. Murray Optics INAF/Brera G. Pareschi Thin shell Wolter I with polynominal figure Shells similar to XMM but glass 5

6 Si pore optics Athena+ - ESA Making the Si pore stacks approximate Wolter I surfaces Si wafers cut ribs Deposit wedge Apply high Z coating (Gold, Iridium ) between ribs Cold weld plates together with curvature 6

7 Si pore optics Athena+ ESA Si pore module Cosine Research Focal length F=12m Original rib spacing 0.83 mm Radial width Δr=0.605 mm Axial length 4.F.Δr/R Wolter-Schwartzschild geometry Gap between 1 st and 2 nd surface - spherical 7

8 Wide field Si pore optics Wide rib spacing Module layout to populate aperture 8

9 Wide field Si pore optics WFXT Grasp 0.37 m 2 deg 2 at 1 kev m 2 deg 2 at 4 kev m 2 deg 2 at 6.5 kev Original pore geometry grasp 0.19 m 2 deg 2 at 1 kev Wide field pore geometry grasp 0.5 m 2 deg 2 at 1 kev HEW limited by conical approximation Can be improved by including axial curvature 9

10 Athena+ area vs. energy Using Ir coating a C overcoat increases the low energy area 10

11 Line: Lobster module F=300 mm Soft X-ray Transient Astronomy Red points: Swift BAT short GRBs Black points: Swift BAT long GRBs? Green points: Swift XRT GRB afterglows Want ~1 arc min over 30 degree FOV with collecting area ~ 10 cm 2

12 X-ray Transient Imaging Require: FOV ~30 by 30 degrees or larger Continuous coverage ~1000 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 Wolter I: FOV diameter limited to ~twice grazing angle - only ~2 o Could use a fly s-eye of small Wolter I s but very inefficient 2 in-plane reflections - lateral inversion in the image plane Solution: Angel Square pore or Kirkpatrick-Baez geometry 12

13 Square pore geometry - Angel Focusing by 2 reflections from adjacent walls of a square pore Reflection planes orthogonal - No lateral inversion in image plane Focusing independent of rotation of pore about pore axis φ Pores on spherical surface radius R Pore axes point to common centre of curvature Image on a spherical surface radius f=r/2 NO limit to the FOV

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15 Square Pore MCPs Glass plate - thickness 1-2 mm transmission ~67% Pores d~20 μm, wall~4 μm, L/d~100 K-B stacks 15

16 Pore packing geometries Cartesian packing Lobster Eye - high aperture utilization but correlated single reflection background Random packing inefficient use of aperture Waffle packing -redistribute the single reflection background but retain high aperture utilization No centre of symmetry no preferred axis optimum for wide field imaging Octagonal packing, φ=45 degrees Radial packing, φ=0 degrees With radial packing require tandem plates to approximate Wolter I imaging Optimum for narrow field imaging

17 Plate imperfections: Lobster eye PSF Figure errors and surface roughness of the channel walls 4.5 Å rms Misalignment of the channel axes ± 1 arc mins Channel rotation errors ± 1 degree Channel shear ~1/40 of channel pitch Focal length 500 mm Channel L/D 50 1 st cross-arm zero 2FD/L=20 mm HEW of core ~ 4.8 arc mins FWHM ~ 3 arc mins Focusing gain ~

18 Measured PSF FWHMY = arcmin (depending on plate scale Linearisation) FWHMX = arcmin (depending on plate scale Linearisation)

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39 Lobster eye collecting area Total collecting area ~22 cm 2 at 1 kev ~ 30% of area in central focused spot Crab ~93 cts/sec 39

40 10 x Lobster modules Total FOV ~9000 sq degrees 6 degree cant angle of modules 240mm square Lobster optics frames, 500mm focal length Angular resolution ~3 arc mins Collecting area ~9 cm 2 at 1 kev

41 K-B Stack Schmidt Geometry 41

42 K-B Si Pore module Module shown is a Wolter I conical approximation prototype Could easily be constructed in the Kirkpatrick Baez geometry 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 42

43 Packing of K-B stacks into an aperture Si stacks suitable for larger instruments Focal length 5 m (needs to be > ~2.5 m) Collecting area ~100 cm 2, angular resolution ~20 arc seconds Sensitivity 5-50 better than Lobster module F=500 mm Narrow field - pointed wide field - survey 43

44 Wide field K-B stack Vignetting at 1 kev 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 Focusing gain ~13300 Area at 13 cm 2 at 6.5 kev Area vs. energy HEW limited by flat plates can be improved using axially curved plates 44

45 Summary Si pore optics modules with wide rib spacing and spherical join plane (Wolter-Schwartzschild) can provide grasp >= WFXT better than 10 arc sec imaging over 1 degree FOV can be improved by introducing axial curvature Glass square pore MCPs provide ~4 arc min imaging and focusing gain of ~ by 30 degree FOV area ~9 cm 2 at 1 kev 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 A new class of instrument deep wide field imaging faint transient imaging 45