X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa X-Ray Polarimetry with a Micro Pattern Gas Detector with Pixel Read-out Ronaldo Bellazzini INFN - Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Polarization from celestial sources may derive from: Emission processes themselves: cyclotron, synchrotron, non-thermal bremmstrahlung (Westfold, 1959; Gnedin & Sunyaev, 1974; Rees, 1975 Scattering on aspherical accreting plasmas: disks, blobs, columns. (Rees, 1975; Sunyaev & Titarchuk, 1985; Mészáros, P. et al. 1988) Vacuum polarization and birefringence through extreme magnetic fields (Gnedin et al., 1978; Ventura, 1979; Mészáros & Ventura, 1979) Why X-ray Astrophysical Polarimetry?

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Polarization from Supernova Remnants: The Crab case Crab-Nebula shows the same degree and angle of polarization from radio to X-rays and this is a signature of synchrotron emission. Radio (VLA) Optical (Palomar) Infrared (Keck) X-rays (Chandra)

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa X-ray polarimetry offers a definitive test of strong field gravity near very compact sources: Black Hole binaries, Neutron Stars and microquasars... Unlike spectral data, polarization data are strongly affected by general relativistic effects. For example: A BH is surrounded by an optically thick and geometrically thin accretion disk. Heigher energy photons come from smaller disk radii. As a consequence, as the photon energy increases from 1 to 10 KeV, the plane of linear polarization will swing smoothly trough an angle of ˜27° for a 9 Solar Mass BH and 40º for an extreme Kerr BH (for an inclination of 41º). This effect is due to the strong gravitational bending of light rays.

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Simulated view of an accretion disk around a black hole as it appears to a distant observer - Light bending makes visible the bottom part of a disk. - Doppler boosting produce an increased intensity of one-side Polarimetry would add to energy and time two further observable quantities, the amount and the angle of polarization, constraining any model and interpretation: a theoretical/observational breakthrough.” P. Meszaros et al Accreting X-ray Pulsar

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Heitler W.,The Quantum Theory of Radiation The photo-electric effect is very sensitive to photon polarization Polarization information is derived from the track of the photoelectrons imaged by a finely subdivided gas detector

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Dependence of polar angle of photo-electron in Ne

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa The photoelectron is slowed by ionizing collisions with outer electrons of the atoms of the medium. The energy loss increases with decreasing kinetic energy (Bethe law for low energy). Electrons are also scattered by charges in the nuclei with no significant energy loss. This follows the screened Rutherford law : While scattering crucially depends on the atomic number, slowing down is only moderately dependent. The photoelectron leaves in the absorber a string of electron/ion pairs, marking the path from its creation to the stopping point. We call this cluster a “track”: in the initial part of this track resides the information on the original electron direction and thence the key to derive the polarization of the photon. This dependence is preserved if the track is projected onto a plane perpendicular to the radiation. Basics of photoeffect in gases

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Projection of MC photoelectron tracks

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa The micro-pattern gas detector scheme

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa The overall detector assembly and read-out electronics

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa The anode charge collection plane

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Microscope picture of the GEM structure Microscope picture of the pixelized read-out

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Electric field structure X ray gas mixture: - Ne / Ar / Kr ….. - Methane/ Ethane C02, DME… ns  E X photon (E) PCB GEM pixel conversion gain collection

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa 5.9 KeV electrons

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Angular distribution 5.9 KeV unpolarized source 5.4 KeV polarized source Modulation factor = (Cmax – Cmin)/ (Cmax + Cmin) ˜ 50% at 6 KeV MDP scales as:for bright sources for faint sources

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Scatter plot of the baricenters relative to the reconstructed impact point 5.9 KeV unpolarized source 5.4 KeV polarized source No rotation of the detector is needed!

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa 5.9 KeV unpolarized source 5.4 KeV polarized source

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Red line – direction of the photoelectrons using the baricenter information Green line – reconstructed direction using impact point

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Imaging capability BaricentersImpact points

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa Present and optimized configuration for astrophysical applications

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa PCB read-out anodes Next technological step VLSI pixel chip from digital X-ray camera

X-Ray Polarimetry with Micro Pattern Gas Detectors Nuclear Science Symposium – November 2001 R.Bellazzini - INFN Pisa According to Nature….. “ the work is highly significant for high energy astrophysics and astronomy in general. X-ray polarimetry is a unique probe of particle acceleration in the universe. It will provide a new tool for studying the fascinating and poorly understood jet sources. The instrumentation described here will very likely revolutionize this area of study …..”