2 Why X-ray Astrophysical Polarimetry ? Polarization from celestial sources may derive from:Emission processes themselves:cyclotron, synchrotron, non-thermal bremsstrahlung(Westfold, 1959; Gnedin & Sunyaev, 1974; Rees, 1975Scattering 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)
3 Astrophysics with XIPE 2.1 Acceleration phenomena– Supernova Remnants– Pulsar Wind Nebulae– Jets– mQSOs– Blazars & Radiogalaxies– Magnetic reconnection- solar flares2.2 Emission in strong magnetic fields– Accreting White Dwarfs– Millisecond X-ray pulsars– Accreting X-ray pulsars
4 2.3 Scattering in aspherical situations – X-ray binaries– Radio-quiet AGNs– X-ray reflection nebulaeFundamental physics with XIPE3.1 QED in strong magnetic fields3.2 General Relativity in extreme gravity fields3.3 Quantum Gravity3.4 Search for axion-like particles
5 Measurement of the polarization of the radiation.
6 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.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 cos2 (φ), therefore it is preferentially emitted in the direction of the electric field.Being the cross section always null for φ = 90o the modulation factor µ equals 1 for any polar angle.Heitler W.,The Quantum Theory of RadiationCosta, Nature, 2001β =v/cBy measuring the angular distribution of the emission direction of the ejected photoelectrons (the modulation curve) it is possible to derive the X-ray polarization.
7 The principle of detection X-ray polarimetry with a Gas Pixel DetectorTo efficiently image the track at energies typical of conventional telescopes IASF-Rome and INFN-Pisa developed the Gas Pixel detector. The tracks are imaged by using the charge.The principle of detectionGEM electric fieldA photon cross a Beryllium window and it is absorbed in the gas gap, the photoelectron produces a track. The track drifts toward the multiplication stage that is the GEM (Gas Electron Multiplier) which is a kapton foil metallized on both side and perforated by microscopic holes (30 um diameter, 50 um pitch) and it is then collected by the pixellated anode plane that is the upper layer of an ASIC chip.pixelGEM20 nsaEX photon (E)PCBconversiongaincollectionCosta et al., 2001, Bellazzini et al.2006, 2007Polarization information is derived from the angular distribution of the emission direction of the tracks produced by the photoelectrons.The detector has a very good imaging capability.Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory
8 Tracks reconstruction 1) The track is collected by the ASIC2) Baricenter evaluation (using all the triggered pixels)3) Reconstruction of the principal axis of the track: maximization of the second moment of charge distribution4) Reconstruction of the conversion point: third moment along the principal axis (asymmetry of charge distribution to select the lower density end) + second moment (length) to select the region for conversion point determination).5) Reconstruction of emission direction: (maximization of the second moment with respect to the conversion point ) but with pixels weighted according to the distance from it.2013/08/25SPIE Optics + Photonics, San Diego August 2013
9 The Galactic Center Black Hole Laboratory ASIC features pixels 50 μm pitchPeaking time: 3-10 ms, externally adjustable;Full-scale linear range: electrons;Pixel noise: 50 electrons ENC;Read-out mode: asynchronous or synchronous;Trigger mode: internal, external or self-trigger;Read-out clock: up to 10MHz;Self-trigger threshold: 2200 electrons (10% FS);Frame rate: up to 10 kHz in self-trigger mode(event window);Parallel analog output buffers: 1, 8 or 16;Access to pixel content: direct (single pixel) or serial(8-16 clusters, full matrix, region of interest);Fill fraction (ratio of metal area to active area): 92%)1.5 cmThe chip is self-triggered and low noise. It is not necessary to readout the entire chip since it is capable to define the sub-frame that surround the track. The dead time downloading an average of 1000 pixels is 100 time lower with respect to a download of 105 pixel.Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory
10 The Galactic Center Black Hole Laboratory Extensively tested, with thermal-vacuum cycles, it has been vibrated, irradiated with Fe ions and calibrated with polarized and unpolarized X-rays..The real implementation of a working GPD prototype.HE-DME mixture: sensitive range 2-10 keVElectronicsTitanium FrameBeryllium window9 cmDME = (CH3)2O60 µm/√cm diffusionWeight of the GPD + Lab Electronics = 2 kgPower Consumption of the GPD + Lab Electronics = 5 WGranada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory
11 IASF-Rome facility for the production of polarized X-rays. Close-up view of the polarizer and the Gas Pixel DetectorFacility at IASF-Rome/INAFkeV Crystal Line Bragg angleADP(101) CONTPET(002) CONTRh(001) Mo LαGraphite CONTAl(111) Ca KαCaF2(220) Ti KαLiF(002) FeGe(333) Cu KαFLi(420) Au LαFli(800) Mo KαCapillary plate (3 cm diameter)Aluminum and Graphite crystals.Spectrum of the orders of diffraction from the Ti X-ray tube and a PET crystal acquired with a Si-PiN detector by AmptekPET(Muleri et al., SPIE, 2008)Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory
12 Not only MonteCarlo: Our predictions are based on data Each photon produces a track. From the track the impact point and the emission angle of the photoelectron is derived. The distribution of the emission angle is the modulation curve.Not only MonteCarlo: Our predictions are based on dataMuleri et al. 2007Impact pointThe modulation factor measured 2.6 keV, 3.7 keV and 5.2 keV has been compared with the Monte Carlo previsions. The agreement is very satisfying.By rotating the polarization vector the capability to measure the polarization angle is shown by the shift of the modulation curve.Present level of absence ofsystematic effects (5.9 keV).Bellazzini 2010Soffitta et al., 2010Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory
13 More energies, more mixtures Pure DME (CH3)2OModulation curve at 2.0 keVμ = 13.5%We performed measurement at more differentenergies and gas mixtures.(Muleri et al., 2008, 2010).
14 The imaging properties of the GPD. Panter X-ray facility (MPE, Germany):JET-X (Telescope, same as Swift, ~1mm/arcmin)Focal Length (3.5 m)JET-X HEW (4.5 keV) : 18’’JET-X + GPD (HEW) : 23.2’’ (394 m )IAPS/INAF laboratory :Very narrow pencil beam.Detector shifts : 300 m.Position resolution : 30 m (rms).Half Energy Width : 93 mSpiga et al., 2013, Fabiani et al. 2013Imaging properties are mainly driven by the optics.
16 A Gas Pixel Detector for higher energies (6-35 keV) Ar-DME 2-atm; 2-barEfficiency (dashed) and modulation Factor (solid) with Monte Carlo and measurement for the low energy (2-10 keV) polarimeter and medium energy (6-35 keV) polarimeter.
17 Riunione Nazionale Astronomia X 15-16/11/2012 P. Soffitta Compton PolarimetryTriggered by the effective area at high energy up to 80 keV of the mirror foreseen for NHXM but exploiting the heritage of previews works on Compton Polarimetry We re-started such activity.Angular depandance of Compton effect.Riunione Nazionale Astronomia X /11/2012 P. SoffittaCosta et al. NIM 1995Soffitta et al., SPIE 2010
18 Riunione Nazionale Astronomia X 15-16/11/2012 P. Soffitta
19 Riunione Nazionale Astronomia X 15-16/11/2012 P. Soffitta By using GEANT 4 and a Monte Carlo specifically developed at this purpose we evaluated the tagging efficiency as a function of energy by using the two measured values at 22 keV and 60 keV. The sensitivity estimation on the right performed for a configuration similar to that of the experimental laboratory set-up is based on an experimental measurement of the efficiency.Riunione Nazionale Astronomia X /11/2012 P. Soffitta
20 NHXPM GEMSEnergy range(keV) Energy range (keV)LEP (2-10) (2-10)MEP (6-35)HEP (20-80) not includedin the propos.Angular resolutionLEP (15 ‘’) arcminMEP (20 ‘’)
21 MDP HEPThe laboratory measurements confirm the anticipation of the Monte Carlo simulation.NHXM GEMSEnergy range(keV) Energy range (keV)LEP (2-10) (2-10)MEP (6-35)HEP (20-80) not includedin the propos.Angular resolutionLEP (15 ‘’) arcminMEP (20 ‘’)GEMS : MDP is 0.01 for a 10 mCrab source with an observation of 3.3 x 105seconds For NHXM LEP it would take around 106 s.
23 Different Scenarios (Concepts) Polarimetry is an [almost] undisclosed domain of X-ray Astronomy.It can be performed, with guaranteed results and with a large discovery space, in many different scenarios.1) Baseline. Photoelectric Polarimetry with at 2-10keV GPD (imaging focal plane) for a:Small (POLARIX, IXPE, XIPE, …)Medium (NHXM-LEP)Large (XEUS, IXO)2) Extended versionsExtend the band of GPD to higher energies 5-35 keV (NHXM-MEP)Non imaging focal plane scattering polarimeter (NHXM-HEP)3) Descooped versionsArray of GPDs with collimator both LEP and/or MEP4) Side versionsPolarimetry of transients (GRB,SGR) with Wide Field InstrumentsPolarimetry of solar flaresAll these concepts produce valuable results (but costs and throughput are not the same)
24 Possibili collaborazioni con la Cina. Universita’ Tsinghua (Beijing)Pi Prof. Hua Feng. Contributo italiano Gas Pixel detector come imager e contatori di fotoni ma con finestra sottile.Pulsar X isolate e Blazars.
25 ESA-CAS joint mission Call end 2014 two years study four years implementationlaunch 2021Payload requirement :- Mass 60 kg- Power 50 Watts- Satellite weight 250 kgSpiga et al., 2014XIPE non puo’ essere riproposto con gli specchi di JET-X (70 kg ognuno). Proponiamo XILPE (XIPE Light) in cui I mandrini di JET-X possono essere riutilizzati per realizzare un payload entro i limiti :XIPE : Enrico Costa, Paolo Soffitta (IAPS/INAF). Ronaldo Bellazzini (INFN-Pisa), Hua Feng (Tsinghua University); Wang (Tonji University, Shanghai).
26 RisorseScientific capabilityEnergy range2-10 keV for polarimetryPolarization sensitivity20 % at 1 mCrab 105 sImaging capability (overall)23’’ HEW, 15’ x 15’ FoVSpectroscopic capability20 % at 6 keVTiming8 µs, 10 s dead timeBackground (point source)20 nCrabCrab rate47 c/sTelemetry29 kbit (typical 0.4 Crab)Payload PowerWattGPD + Filter Wheel (FW)2 (typical)8 (peak FW)Mirror Thermal control10 (peak)Back End Electronics12Control Electronics1648Payload Mass(kg)GPD + Filter wheel + Box3.3X-ray Telescope15Back End Electronics1.6Control Electronics5Optical bench and Telescope Tube5 (TBV)29.9Payload VolumeGPD + Filter Wheel + Box23.0 cm x 16.5 cm x 18.0 cm (L,L,H)Bee (20 cm max from GPD)19.0 cm x 13.8 cm x 10.8 cm (L,L,H)Control Electronics (anywhere)28.5 cm x 11 cm x 21 cm (L,L,H)Mirror30 cm (diameter); 60 cm (length)Focal length350 cmAbbiamo inoltre una presentazione di SEEPE Solar energetic emission and particle explorer.Siming Liu (PMO), Paolo Soffitta (IAPS/INAF), Ronaldo Bellazzini (INFN-Pisa), Robert Wimmer (Kiel)Una missione pensata per essere complementare a solar-orbiter ma senza ottiche a bordo.