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arXiv · 2608.20898

EXPO: a quantum leap in fast, wide-band X-ray polarimetry for astrophysics

Paolo Soffitta·Sebastien Guillot·Ian Hutchinson·Fabio Muleri·Mark Pearce·Andrea Santangelo·Daniele Spiga·Ivan Agudo·Gino Bruno Amata·Jaroslaw Bakala·Elisabetta Baracchini·Stefano Basso·Jorg Bayer·Benedikt Bergmann·Jaroslaw Borek·Enrico Bozzo·Soren Krinstian Brandt·Carl Budtz-Jorgensen·Vadim Burwitz·Stefano Cesare·Jerome Chenevez·Enrico Costa·Elisa Costantini·Vincenzo Cotroneo·Walter Cugno·Riccardo Ferrazzoli·Nicolas De Angelis·Desiree Della Monica Ferreira·Klaus Desch·Giorgio Dho·Giuseppe Di Persio·Sergio Fabiani·Davide Fiorina·Szymon Gburek·Markus Gruber·Allan Hornstrup·Jennifer Jones·Jochen Kaminski·Mozsi Kiss·Irfan Kuvvetli·Carlo Lefevre·Hannah Lerman·Honghui Liu·Pasqualino Loffredo·Niels Lund·Hemanth Manikantan·Melissa McHugh·Paul O'Brien·Stephane Paltani·Giovanni Pareschi·Stefano Piacentini·Vladislavs Plesanovs·John Rankin·Ajay Ratheesh·Selina Ringsborg Howalt Owe·Alda Rubini·Miguel Andres Sanchez Carrasco·Emanuele Scalise·Konrad R. Skup·Gianpiero Tagliaferri·Chris Tenzer·Berend Winter·Silvia Zane·Lorenzo Amati·Alessio Anitra·Maria Cristina Baglio·Thibault Barnouin·Stefano Bianchi·Fabrizio Bocchino·Markus Boettcher·Niccolo Bucciantini·Sara Capecchiacci·Fiamma Capitanio·Martina Cardillo·Eugene Churazov·Stefano Covino·Filippo D'Ammando·Laura Di Gesu·Alessandro Di Marco·Tiziana Di Salvo·Michal Dovciak·Lorenzo Ducci·Hua Feng·Giorgio Galanti·Giancarlo Ghirlanda·Vittoria Elvezia Gianolli·Andrea Gnarini·Emanuele Greco·Jeremy Heyl·Adam Ingram·Svetlana Jorstad·Philip Kaaret·Ildar Khabibullin·Fabian Kislat·Henric Krawczynski·Josefin Larsson·Ioannis Liodakis·Frederic Marin·Andrea Marinucci·Lorenzo Marra

Abstract

The Enhanced X-ray Polarimetry Observatory (EXPO) is a mission concept proposed to ESA as an M8 candidate, with a prospective launch in 2041. Building on the scientific success of IXPE, EXPO is designed to overcome its two main limitations, the narrow 2-8 keV energy band and the very slow repointing time, and to enable new scientific capabilities. A wide energy band and fast repointing are essential for investigating the hard X-ray emission of magnetars and black-hole binaries, particle acceleration in supernova remnants and pulsar-wind nebulae, radiative transfer in highly magnetized plasmas, X-ray reflection in accretion flows and active galactic nuclei, and the prompt and afterglow emission of gamma-ray bursts and magnetar flares. EXPO comprises five focusing X-ray telescopes and gas photoelectric polarimeters based on the Timepix ASIC family with InGrid amplification, enabling three-dimensional track imaging and operation in the 2-35 keV band through optimized low- and medium-energy detector configurations. The mirror modules use proven electroformed nickel technology with Au-C coatings and an XMM-like focal length of 7.5 m. The polarimeters are complemented by a coded-mask Wide Field Instrument (WFI), derived from SVOM/ECLAIRs for continuous monitoring of a 2 sr field of view; a Spectral Imaging Camera (SIC), based on stacked CMOS and CdTe detectors for broadband imaging spectroscopy and accurate spectro-polarimetric decomposition; and an Instrument Control Unit (ICU) for payload management, onboard WFI image reconstruction, transient identification, and autonomous spacecraft repointing requests. These capabilities extend X-ray polarimetry into the hard X-ray domain and open a new observational window on fast transients, time-domain astrophysics, and multi-messenger astronomy.

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Paolo Soffitta, Sebastien Guillot, Ian Hutchinson, Fabio Muleri, Mark Pearce, Andrea Santangelo, Daniele Spiga, Ivan Agudo, Gino Bruno Amata, Jaroslaw Bakala, Elisabetta Baracchini, Stefano Basso, Jorg Bayer, Benedikt Bergmann, Jaroslaw Borek, Enrico Bozzo, Soren Krinstian Brandt, Carl Budtz-Jorgensen, Vadim Burwitz, Stefano Cesare, Jerome Chenevez, Enrico Costa, Elisa Costantini, Vincenzo Cotroneo, Walter Cugno, Riccardo Ferrazzoli, Nicolas De Angelis, Desiree Della Monica Ferreira, Klaus Desch, Giorgio Dho, Giuseppe Di Persio, Sergio Fabiani, Davide Fiorina, Szymon Gburek, Markus Gruber, Allan Hornstrup, Jennifer Jones, Jochen Kaminski, Mozsi Kiss, Irfan Kuvvetli, Carlo Lefevre, Hannah Lerman, Honghui Liu, Pasqualino Loffredo, Niels Lund, Hemanth Manikantan, Melissa McHugh, Paul O'Brien, Stephane Paltani, Giovanni Pareschi, Stefano Piacentini, Vladislavs Plesanovs, John Rankin, Ajay Ratheesh, Selina Ringsborg Howalt Owe, Alda Rubini, Miguel Andres Sanchez Carrasco, Emanuele Scalise, Konrad R. Skup, Gianpiero Tagliaferri, Chris Tenzer, Berend Winter, Silvia Zane, Lorenzo Amati, Alessio Anitra, Maria Cristina Baglio, Thibault Barnouin, Stefano Bianchi, Fabrizio Bocchino, Markus Boettcher, Niccolo Bucciantini, Sara Capecchiacci, Fiamma Capitanio, Martina Cardillo, Eugene Churazov, Stefano Covino, Filippo D'Ammando, Laura Di Gesu, Alessandro Di Marco, Tiziana Di Salvo, Michal Dovciak, Lorenzo Ducci, Hua Feng, Giorgio Galanti, Giancarlo Ghirlanda, Vittoria Elvezia Gianolli, Andrea Gnarini, Emanuele Greco, Jeremy Heyl, Adam Ingram, Svetlana Jorstad, Philip Kaaret, Ildar Khabibullin, Fabian Kislat, Henric Krawczynski, Josefin Larsson, Ioannis Liodakis, Frederic Marin, Andrea Marinucci, Lorenzo Marra. 2026-08-21. EXPO: a quantum leap in fast, wide-band X-ray polarimetry for astrophysics. https://arxiv.org/abs/2608.20898

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