Thesis

Development of a Polarimeter for AstroMeV ESA Space Mission Proposal

• Call:

  IDPASC Portugal - PHD Programme 2014

• Academic Year:

  2014 /2015

• Domain:

  Astrophysics

• Supervisor:

  Rui Curado da Silva

• Co-Supervisor:

  Jorge Maia

• Institution:

  Universidade de Coimbra

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  Polarimetry in hard X- and soft gamma-ray astrophysics is still a quite unexplored domain due to the great deal of complexity that this kind of measurement requires. In fact no dedicated polarimeters have ever been launched into space. To date gamma-ray source emissions have been studied almost exclusively through spectral, timing variability analysis of the measured fluxes and by using imaging techniques based on coded mask cameras or telescopes equipped with high efficiency focal plane detectors. By measuring the polarization angle and degree of linear polarization of the detected emission, it is increased by two the number of observational parameters thereby allowing better discrimination between different models. Polarimetric observations can provide important information about geometries, magnetic fields, composition and emission mechanisms in a wide variety of gamma-ray sources such as: pulsars, solar flares, active galactic nuclei, galactic black holes or gamma-ray bursts [1]. LIP - Coimbra has been developing for more than a decade both CdZnTe polarimeter prototypes and mass model simulation code for space polarimetry [2, 3]. Our group has also joined the latest major X- and gamma-ray telescope mission proposals to ESA Cosmic Vision, like DUAL or XIPE, where the main instrument was optimized for polarization measurements [4, 5]. In response to ESA M4 Call for Missions that will be announced in the second half of August 2014, our group together with other european partners will submit to ESA the AstroMeV proposal (http://astromev.in2p3.fr/). AstroMeV is a square-meter class instrument composed of two main detectors: a gamma-ray tracker made of a stack of semiconductor detectors (Si and/or CdTe) and a calorimeter composed of an ensemble of position-sensitive scintillator modules. The mission should carry WPOL wide field camera, which aims to monitor the X-ray/gamma-ray sources and to measure their polarimetric properties. This camera will be used in space to alert the main instrument in case of transient events (gamma-ray bursts, black hole binaries state transition, supernovae, etc.) and to map the X-ray/gamma-ray polarized sources in our Galaxy, which has never been done up to now. The selected PhD student will contribute to instrument development in the framework of AstroMeV collaboration through focusing system and CdZnTe focal plane prototype testing under polarized beams, through mass model simulation using GEANT4 (http://geant4.web.cern.ch/geant4/) and MEGAlib (http://www.mpe.mpg.de/MEGA/megalib.html) simulation tools [6, 7] and by INTEGRAL satellite polarized source’s observation data analysis. Instrument sensitivity optimization should result in a configuration allowing a minimum detectable polarization lower than 5% (3σ) for mCrab equivalent source and 10^6s observation time. [1] F. Lei, A. J. Dean, and G. L. Hills, “Compton Polarimetry in Gamma-Ray Astronomy”, Space Sci. R., 82, p. 309, 1997. [2] R. M. Curado da Silva, E. Caroli, J. B. Stephen and P. Siffert, “CIPHER, a polarimeter telescope concept for Hard X-ray Astronomy”, Exp. Astron., Vol. 15, nº1, pag. 45-65, 2003. [3] R. M. Curado da Silva, et al., “Polarimetric performance of a Laue lens gamma-ray CdZnTe focal plane prototype”, J. Appl. Phys., 104, p. 084903, 2008. [4] P. von Ballmoos et al., “A DUAL mission for nuclear astrophysics”, Nucl. Instr. and Meth. Section A, 623, pp 431-433, 2010. [5] Paolo Soffitta, R. M. Curado da Silva et al., “XIPE: the X-ray Imaging Polarimetry Explorer”, Experimental Astronomy 2013, DOI: 10.1007/s10686-013-9344-3. [6] S. Agostinelliae, J. Allisonas, K. Amako “Geant4 - a simulation toolkit”, Nucl. Instr. and Meth. A, 506, pp. 250-303, 2003. [7] A. Zoglauer, R. Andritschke and F. Schopper, “MEGAlib – The Medium Energy Gamma-ray Astronomy Library”, New Astronomy Reviews 50 (2006) 629–632