The Lunar Electromagnetic Monitor in X-rays: Concept, Design and Instrument Development

The Lunar Electromagnetic Monitor in X-rays: concept, design and instrument development. E. Del Monte1, Y. Evangelista1, F. Ceraudo1, G. Della Casa1, G. Dilillo1, M. Feroci1, E. Giancarli1,2, G. Lombardi1, A. Nuti1, M. Rapisarda1, G. Bertuccio3, R. Campana4, M. Centis Vignali5, E. Demenev5, F. Ficorella5, M. Fiorini6, A. Gemelli7, M. Grassi7, P. Malcovati7, F. Mele1,3, G. Pepponi5, A. Samusenko5, M. Tambussi7, G. Zampa8, N. Zorzi5, F. Esposito9, U. Cortesi10, I. Donnarumma11, F. D’Amico12, A. Turchi11, M. Gai10, A. Argan12 on behalf of the EMM team, 1INAF – IAPS, Via del Fosso del Cavaliere 100, 00133, Roma (Italy) [email protected], 2Sapienza Università di Roma – Dipartimento di Fisica, Piazzale A. Moro 5, 00185 Roma (Italy), 3Politecnico di Milano – Dipartimento di Elettronica, Informazione e Bioingegneria, Via Ponzio 34/5, 20133 Milano (Italy), 4INAF – OAS, Via Gobetti 93/3, 40129 Bologna (Italy), 5Fondazione Bruno Kessler, Via Sommarive 18, 38123 Povo (Italy), 6INAF – IASF Milano, Via Alfonso Corti 12, 20133, Milano (Italy), 7Università di Pavia – Dipartimento di Ingegneria Industriale e dell'Informazione, Via Adolfo Ferrata 5, 27100 Pavia (Italy), 8INFN – Sezione di Trieste, Padriciano 99, 34149 Trieste (Italy), 9INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli (Italy), 10CNR – Istituto Di Fisica Applicata “Nello Carrara”, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy), 11Agenzia Spaziale Italiana, Via del Politecnico snc, 00133, Roma (Italy), 12INAF – Sede Centrale, Viale del Parco Mellini 84, 00136 Roma (Italy). Context: The surface of the Moon is an interesting and promising platform for an all-sky X-ray observatory. The scientific goal is a continuous observation in search of transients and interesting events in the context of Multi-Messenger Astrophysics [1]. The all-sky coverage can be obtained by exploiting the rotation of the Moon itself. The new interest for the Moon exploration and infrastructures offers great opportunities for this purpose. Description of the project: The Lunar Electromagnetic Monitor in X-rays (LEM-X) is an all-sky X-ray observatory proposed for the surface of the Moon. The building block of LEM-X is a pair of coded aperture cameras, able to image the sky in a field of view of ~2 sr (at zero response) with a source location accuracy of ~1 arcmin. The LEM-X instrument envisages five of such camera pairs, arranged on a dome-shaped structure, to reach a sensitivity better than 1 Crab for short transients (1 s observation) and 5 mCrab for longer observations (50 ks observation) in the 2 – 50 keV energy band, with a spectral resolution better than 350 eV FWHM at 6 keV. We are developing the engineering model of the LEM-X detection system [2] and studying the configuration of LEM-X for the Moon [3]. In particular, each detection system is composed of a linear Silicon Drift Detector connected via wire bondings to two rows of 11 custom developed ASICs [4], all integrated on a ceramic front-end board. Laboratory tests on a reduced scale but representative breadboard of this assembly show an adequate capability of reconstructing the position of the photon interaction on the detector, together with an energy resolution of ~160 eV at 5.9 keV for single-anode events at a temperature of -20 °C. These activies are carried out in the framework of the “Earth-Moon-Mars” (EMM) program, funded in Italy by the Ministero dell'Università e della Ricerca in the framework of the “Piano Nazionale di Ripresa e Resilienza” and lead by the Istituto Nazionale di Astrofisica (INAF) in collaboration with Consiglio Nazionale delle Ricerche (CNR) and Agenzia Spaziale Italiana (ASI). Here we give an update of the LEM-X status, describe the instrument design and show the measured scientific performance of the prototypes. References: [1] Meszaros P. et al. (2019) Nature Reviews Physics, 1, 585–599 [2] Del Monte E. et al. (2024) SPIE Proceedings, 13093, id. 130931U [3] Nuti A. et al. (2024) SPIE Proceedings, 13093, id. 130937O [4] Mele F. et al. (2025) Proceedings of SIE 2024, Lecture Notes in Electrical Engineering, 1263, Springer, Cham