X-ray Polarimetry - INAF-IASF-Roma

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SXRP (Stellar X-ray Polarimeter) • A step forward in the sensitivity was done devising and building a polarimeter based on Bragg diffraction and Thomson scattering in the focus of a large X-ray telescope. • Photons coming from the SODART telescope are diffracted by a thin mosaic graphite crystal at 2.6 keV and 5.2 keV creating a secondary focus. The photons at E > 5 keV that do not satisfy the Bragg condition pass through and are diffused around by a lithium scatterer. 4 position sensitive proportional counters detect simultaneously the radiation. SXRP is in rotation around the telescope axis. • Bragg diffraction saves the images and is more sensitive at low flux, Thomson scattering provides better sensitivity at large fluxes but the image is lost. Kaaret et al., SPIE 1989, Soffitta et al., NIM A, 1998 • 4 x 100 cm 2 imaging proportional counter • Composite window thickness : 150 m for Thomson scattered photons 50 m for Bragg diffracted photons, ø = 3.3 cm ) • Graphite mosaic cristal (50 m thick) • Lithium scatterer 7 cm long and Ø = 3 cm encapsulated in 150 m thick beryllium case • Rotary motor for the ensamble detector/analyser at 1 rpm T=10 5 s. Paolo Soffitta The Extreme and Variable High Energy Sky Chia Laguna 19-21/09/2011
Modern polarimeters dedicated to X-ray Astronomy exploit the photoelectric effect resolving most of the problems connected with Thomson/Bragg polarimeter. The exploitation of the photoelectric effect was tempted very long ago, but only since five-ten years it was possible to devise photoelectric polarimeters mature for a space mission. Heitler W.,The Quantum Theory of Radiation Costa, Nature, 2001 sin cos 5 Z 2 mc 2 7 2 2 2 β =v/c 4 2 r o 4 4 137 h 1 cos By measuring the angular distribution of the ejected photelectrons (the modulation curve) it is possible to derive the X-ray polarization. An X-ray photon directed along the Z axis with the electric vector along the Y axis, is absorbed by an atom. The photoelectron is ejected at an angle θ (the polar angle) with respect the incident photon direction and at an azimuthal angle φ with respect to the electric vector. If the ejected electron is in ‘s’ state (as for the K–shell) the differential cross section depends on cos 2 (φ), therefore it is preferentially emitted in the direction of the electric field. Being the cross section always null for φ = 90 o the modulation factor µ equals 1 for any polar angle. Paolo Soffitta The Extreme and Variable High Energy Sky Chia Laguna 19-21/09/2011
Page 1 and 2: X-Ray Polarimetry Paolo Soffitta IA
Page 3 and 4: Bragg diffraction Bragg diffraction
Page 5 and 6: OSO-8 satellite with a dedicated Br
Page 7: Thomson Polarimeters They were the
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Page 13 and 14: The real implementation of a workin
Page 15 and 16: Each photon produces a track. From
Page 17 and 18: X-ray polarimetry with a micropatte
Page 19 and 20: GRAVITY and EXTREME MAGNETISMS SMAL
Page 21 and 22: The sensitivity to polarization of
Page 23 and 24: POLARIX The missions where the GPD
Page 25 and 26: A detector more tuned on hard X-ray
Page 27 and 28: Spectro-imaging polarimetry of PWNe
Page 29 and 30: Was the GC an AGN a few hundreds ye
Page 31 and 32: IXO: Polarimetry of extended Jets i
Page 33 and 34: For a non focal plane experiment to

X-ray Polarimetry - INAF-IASF-Roma

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