GRI focusing on the evolving violent universe

Authors: Jürgen Knödlseder Peter von Ballmoos Filippo Frontera Angela Bazzano Finn Christensen Margarida Hernanz Cornelia Wunderer

Publish Date: 2008/09/06

Volume: 23, Issue: 1, Pages: 121-138

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Abstract

The gammaray imager GRI is a novel mission concept that will provide an unprecedented sensitivity leap in the soft gammaray domain by using for the first time a focusing lens built of Laue diffracting crystals The lens will cover an energy band from 200–1300 keV with an effective area reaching 600 cm2 It will be complemented by a single reflection multilayer coated mirror extending the GRI energy band into the hard Xray regime down to ∼10 keV The concentrated photons will be collected by a position sensitive pixelised CZT stack detector We estimate continuum sensitivities of better than 10 − 7 ph cm − 2s − 1keV − 1 for a 100 ks exposure the narrow line sensitivity will be better than 3 × 10 − 6 ph cm − 2s − 1 for the same integration time As focusing instrument GRI will have an angular resolution of better than 30 arcsec within a field of view of roughly 5 arcmin—an unprecedented achievement in the gammaray domain Owing to the large focal length of 100 m of the lens and the mirror the optics and detector will be placed on two separate spacecrafts flying in formation in a high elliptical orbit RD work to enable the lens focusing technology and to develop the required focal plane detector is currently underway financed by ASI CNES ESA and the Spanish Ministery of Education and Science The GRI mission has been proposed as class M mission for ESAs Cosmic Vision 2015–2025 program GRI will allow studies of particle acceleration processes and explosion physics in unprecedented detail providing essential clues on the innermost nature of the most violent and most energetic processes in the universeThe GRI mission has been proposed as an international collaboration between in alphabetical order Belgium CSR China IHEP Tsinghua Univ Denmark DNSC Southern Univ France CESR APC ILL CSNSM IAP LAM Germany MPE Ireland UCD School of Physics Italy INAF/IASF Rome Bologna Milano Palermo INAF/OA Brera Roma UNIFE CNR/IMEM Poland NCAC Portugal Combra Univ Evora Univ Russia SINP MSU Ioffe Inst Spain IEECCSICIFAE CNMIMB the Netherlands SRON Utrecht Univ Turkey Sabanci Univ United Kingdom Univ of Southampton MSSL RAL Edinburgh Univ and the United States of America SSL UC Berkeley Argonne National Lab MSFC GSFC US NRLFollowing four years of successful operations INTEGRAL has significantly changed our vision of the gammaray sky 10 The telescopes aboard the satellite have revealed hundreds of sources of different types new classes of objects extraordinary and puzzling views of antimatter annihilation in our galaxy and fingerprints of recent nucleosynthesis processes With the wide fields of view of the IBIS and SPI telescopes INTEGRAL is an exploratorytype mission 11 that allows extensive surveys of the hard Xray and soft gammaray sky providing a census of the source populations and firstever allsky maps in this interesting energy range The good health of the instruments allows continuing the exploration during the upcoming years enabling INTEGRAL to provide the most complete and detailed survey ever which will be a landmark for the discipline throughout the next decadesBased on the INTEGRAL discoveries and achievements there is now a growing need to perform more focused studies of the observed phenomena Highsensitivity investigations of point sources such as compact objects pulsars and active galactic nuclei should help to uncover their yet poorly understood emission mechanisms A deep survey of the galactic bulge region with sufficiently highangular resolution should shed light on the still mysterious source of positrons And a sensitivity leap in the domain of gammaray lines should allow the detection of nucleosynthesis products in individual supernova events providing direct insights into the physics of the exploding starsTechnological advances in the past years in the domain of gammaray focusing using Laue diffraction have paved the way towards a new gammaray mission that can fulfil these requirements Laboratory work and balloon campaigns have provided the proofofprinciple for using Laue lenses as focusing devices in gammaray telescopes 1 7 8 9 and concept studies by CNES and ESA have demonstrated that such an instrument is technically feasible and affordable 3 6 Complemented by a hard Xray telescope based on a singlereflection multilayer coated concentrator a broadband energy coverage can be achieved that allows detailed studies of astrophysical sources at unprecedented sensitivity and angular resolution from ∼10 keV up to at least 1 MeVThe GRI mission deployed in space GRI is composed of two spacecrafts flying in formation at a distance of 100 m The optics spacecraft front carries the Laue crystal lens and the multilayer coated single reflection mirror payloads that concentrate incoming hard Xrays and soft gammarays onto a focal spot situated 100 m behind the spacecraft The detector spacecraft back carrying the detector payload is placed at the location of the focal spot to collected the concentrated photonsThe exploration of the soft gammaray band is complementary to the progress that is presently being made in very highenergy VHE gamma rays by ground based Cherenkov telescopes such as HESS MAGIC or VERITAS The new window opened in the VHE domain resulted so far in more than 50 new sources mainly belonging to the pulsar wind nebulae supernova remnant blazar and mircoquasar source classes In addition AGILE and GLAST will soon provide new vistas of the highenergy gammaray sky in the GeV domain Understanding highenergy emission processes relies heavily on a broad spectral coverage and combining GRI observations with those achieved at GeV and TeV energies will provide unique constraints on the underlying physics

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