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X-ray polarimetry at INAF Paolo Soffitta IAPS/INAF (Rome, Italy) 1 IAPS/INAF : Enrico Costa, Sergio Fabiani, Fabio Muleri, Alda Rubini, Paolo Soffitta.

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Presentation on theme: "X-ray polarimetry at INAF Paolo Soffitta IAPS/INAF (Rome, Italy) 1 IAPS/INAF : Enrico Costa, Sergio Fabiani, Fabio Muleri, Alda Rubini, Paolo Soffitta."— Presentation transcript:

1 X-ray polarimetry at INAF Paolo Soffitta IAPS/INAF (Rome, Italy) 1 IAPS/INAF : Enrico Costa, Sergio Fabiani, Fabio Muleri, Alda Rubini, Paolo Soffitta. INFN-Pisa : Ronaldo Bellazzini, Alessandro Brez, Massimo Minuti, Michele Pinchera, Gloria Spandre.

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, 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)

3 2.1 Acceleration phenomena – Jets – Pulsar Wind Nebulae – Supernova Remnants – m QSOs – Blazars & Radiogalaxies – Magnetic reconnection - solar flares 2.2 Emission in strong magnetic fields – Accreting White Dwarfs – Millisecond X-ray pulsars – Accreting X-ray pulsars Astrophysics with XIPE

4 2.3 Scattering in aspherical situations – X-ray binaries – Radio-quiet AGNs – X-ray reflection nebulae Fundamental physics with XIPE 3.1 QED in strong magnetic fields 3.2 General Relativity in extreme gravity fields 3.4 Search for axion-like particles 3.3 Quantum Gravity

5 Measurement of the polarization of the radiation.

6 Heitler W.,The Quantum Theory of Radiation 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 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. β =v/c By measuring the angular distribution of the emission direction of the ejected photoelectrons (the modulation curve) it is possible to derive the X-ray polarization. Costa, Nature,

7 GEM electric field Polarization 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. pixel GEM 20 ns a E X photon (E) PCB conversion gain collection The principle of detection X-ray polarimetry with a Gas Pixel Detector A 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. To 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. Costa et al., 2001, Bellazzini et al.2006, 2007 Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory7

8 1) The track is collected by the ASIC 2) Baricenter evaluation (using all the triggered pixels) 3) Reconstruction of the principal axis of the track: maximization of the second moment of charge distribution 4) 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. Tracksreconstruction Tracks reconstruction 2013/08/258 SPIE Optics + Photonics, San Diego August 2013

9 ASIC features pixels 50 μm pitch Peaking time: 3-10  s, externally adjustable; Peaking time: 3-10  s, externally adjustable; Full-scale linear range: electrons; Full-scale linear range: electrons; Pixel noise: 50 electrons ENC; Pixel noise: 50 electrons ENC; Read-out mode: asynchronous or synchronous; Read-out mode: asynchronous or synchronous; Trigger mode: internal, external or self-trigger; Trigger mode: internal, external or self-trigger; Read-out clock: up to 10MHz; Read-out clock: up to 10MHz; Self-trigger threshold: 2200 electrons (10% FS); Self-trigger threshold: 2200 electrons (10% FS); Frame rate: up to 10 kHz in self-trigger mode Frame rate: up to 10 kHz in self-trigger mode (event window); (event window); Parallel analog output buffers: 1, 8 or 16; Parallel analog output buffers: 1, 8 or 16; Access to pixel content: direct (single pixel) or serial Access to pixel content: direct (single pixel) or serial (8-16 clusters, full matrix, region of interest); (8-16 clusters, full matrix, region of interest); Fill fraction (ratio of metal area to active area): 92%) Fill fraction (ratio of metal area to active area): 92%) The 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 10 5 pixel. Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory9 1.5 cm

10 . The real implementation of a working GPD prototype. Extensively tested, with thermal-vacuum cycles, it has been vibrated, irradiated with Fe ions and calibrated with polarized and unpolarized X-rays.. DME = (CH3) 2 O 60 µm/√cm diffusion Titanium Frame 9 cm Beryllium window Electronics Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory10 Weight of the GPD + Lab Electronics = 2 kg Power Consumption of the GPD + Lab Electronics = 5 W HE-DME mixture: sensitive range 2-10 keV

11 IASF-Rome facility for the production of polarized X-rays. keV Crystal Line Bragg angle 1.65 ADP(101) CONT PET(002) CONT Rh(001) Mo L α Graphite CONT Al(111) Ca K α CaF 2 (220) Ti K α LiF(002) 55 Fe Ge(333) Cu K α FLi(420) Au L α Fli(800) Mo K α 44.8 Facility at IASF-Rome/INAF Close-up view of the polarizer and the Gas Pixel Detector Capillary 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 Amptek (Muleri et al., SPIE, 2008) PET Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory11

12 Not only MonteCarlo: Our predictions are based on data The 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. 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. By rotating the polarization vector the capability to measure the polarization angle is shown by the shift of the modulation curve. Muleri et al Soffitta et al., 2010 Present level of absence of systematic effects (5.9 keV). Bellazzini 2010 Impact point Granada, 19-22, Nov.2013The Galactic Center Black Hole Laboratory12

13 More energies, more mixtures We performed measurement at more different energies and gas mixtures. Pure DME (CH 3 ) 2 O μ = 13.5% Modulation curve at 2.0 keV (Muleri et al., 2008, 2010).

14 The imaging properties of the GPD. IAPS/INAF laboratory : Very narrow pencil beam. Detector shifts : 300  m. Position resolution : 30  m (rms). Half Energy Width : 93  m 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 ) Spiga et al., 2013, Fabiani et al Imaging properties are mainly driven by the optics.

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16 A Gas Pixel Detector for higher energies (6-35 keV) Ar-DME 2-atm; 2-bar Efficiency (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 Triggered 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. Costa et al. NIM 1995 Soffitta et al., SPIE 2010 Compton Polarimetry

18 Riunione Nazionale Astronomia X 15-16/11/2012 P. Soffitta

19 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.

20 NHXPM GEMS Energy range(keV) Energy range (keV) LEP (2-10) (2-10) MEP (6-35) HEP (20-80) not included in the propos. Angular resolution LEP (15 ‘’) 12 arcmin MEP (20 ‘’)

21 The laboratory measurements confirm the anticipation of the Monte Carlo simulation. MDP HEP GEMS : MDP is 0.01 for a 10 mCrab source with an observation of 3.3 x 10 5 seconds. For NHXM LEP it would take around 10 6 s. NHXM GEMS Energy range(keV) Energy range (keV) LEP (2-10) (2-10) MEP (6-35) HEP (20-80) not included in the propos. Angular resolution LEP (15 ‘’) 12 arcmin MEP (20 ‘’)

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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 versions Extend the band of GPD to higher energies 5-35 keV (NHXM-MEP) Non imaging focal plane scattering polarimeter (NHXM-HEP) 3) Descooped versions Array of GPDs with collimator both LEP and/or MEP 4) Side versions Polarimetry of transients (GRB,SGR) with Wide Field Instruments Polarimetry of solar flares All 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 implementation launch 2021 Payload requirement : - Mass 60 kg - Power 50 Watts - Satellite weight 250 kg XIPE 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). Spiga et al., 2014

26 Risorse Scientific capability Energy range2-10 keV for polarimetry Polarization sensitivity20 % at 1 mCrab 10 5 s Imaging capability (overall)23’’ HEW, 15’ x 15’ FoV Spectroscopic capability20 % at 6 keV Timing 8 µs, 10  s dead time Background (point source)20 nCrab Crab rate47 c/s Telemetry29 kbit (typical 0.4 Crab) Payload PowerWatt GPD + Filter Wheel (FW) 2 (typical) 8 (peak FW) Mirror Thermal control10 (peak) Back End Electronics12 Control Electronics16 48 Payload Volume GPD + Filter Wheel + Box 23.0 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 cm Payload Mass(kg) GPD + Filter wheel + Box3.3 X-ray Telescope15 Back End Electronics1.6 Control Electronics5 Optical bench and Telescope Tube 5 (TBV) 29.9 Abbiamo 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.

27 27/37 XTP (Possible) Instruments. Prima versione High-energy Collimated Array (1-100 keV) Low-energy Collimated Array ( keV) High-energy Focused Array (1-100 keV) All Sky Monitor (5-300 keV) Polarization Observation Telescope (2-10 keV) Low-energy Focused ( keV) 4 m focal length SDD/CZT CCD SCD GEM CZT

28 Past collaboration with China for X-ray polarimetry HXMT


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