Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038

¹ Center for Astro, Particle, and Planetary Physics, New York University Abu Dhabi, PO Box 129188 Abu Dhabi, UAE
e-mail: mcb19@nyu.edu
² INAF – Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate (LC), Italy
³ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain
e-mail: cotizelati@ice.csic.es
⁴ Institut d’Estudis Espacials de Catalunya (IEEC), Carrer Gran Capità 2–4, 08034 Barcelona, Spain
⁵ Departament de Física Quàntica i Astrofísica, Universitat de Barcelona (UB), c/ Martí Franquès 1, 08028 Barcelona, Spain
⁶ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), c/ Martí Franquès 1, 08028 Barcelona, Spain
⁷ INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
⁸ Department of Physics and Astronomy, University of Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone (RM), Italy
¹⁰ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Rome, Italy
¹¹ Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Rome, Italy
¹² ASI – Agenzia Spaziale Italiana, Via del Politecnico snc, 00133 Rome, Italy
¹³ Yunnan Observatories, Chinese Academy of Sciences, 650216 Kunming, PR China
¹⁴ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, PR China
¹⁵ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, PR China
¹⁶ University of Chinese Academy of Sciences, Beijing 100049, PR China
¹⁷ Research Center for Intelligent Computing Platforms, Zhejiang Laboratory, Hangzhou 311100, PR China
¹⁸ CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, PR China
¹⁹ School of Astronomy and Space Science, University of Science and Technology of China, Hefei, PR China
²⁰ Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, PR China
²¹ Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain
²² Division of Engineering, New York University Abu Dhabi, PO Box 129188 Saadiyat Island, Abu Dhabi, UAE
²³ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
²⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
²⁵ Instituto de Astrofísica de Canarias (IAC), Vía Láctea s/n, 38205 La Laguna, S/C de Tenerife, Spain
²⁶ Departamento de Astrofísica, Universidad de La Laguna, Avda. Astrofísico Francisco Sánchez s/n, 38206 La Laguna, S/C de Tenerife, Spain

Received: 14 March 2023
Accepted: 17 July 2023

Abstract

Transitional millisecond pulsars are an emerging class of sources that link low-mass X-ray binaries to millisecond radio pulsars in binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray to optical pulsations are observed only during the high mode. The root cause of this puzzling behaviour remains elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar prototype, PSR J1023+0038, covering from the radio to X-rays. The campaign was carried out over two nights in June 2021 and involved 12 different telescopes and instruments, including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA, and FAST. By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with ALMA at the high-to-low mode switch. The pulsar is subsequently re-enshrouded, completing our picture of the mode switches.