Discovery of two new millisecond pulsars toward the Galactic bulge

¹ NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
² University of Maryland, Department of Astronomy, College Park, MD 20742, USA
³ LAPTh, CNRS, USMB, 74940 Annecy, France
⁴ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁵ Australia Telescope National Facility, CSIRO, Space and Astronomy, PO Box 76, Epping, NSW 1710, Australia
⁶ Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia
⁷ George Mason University, resident at the Naval Research Laboratory, Washington, DC 20375, USA
⁸ Department of Engineering and Physics, Sweet Briar College, Sweet Briar, VA 24595, USA
⁹ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
¹⁰ Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
¹¹ National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA
¹² INAF - Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
¹³ Max-Planck-Institut für Radioastronomie, Auf dem Huügel 69, 53121 Bonn, Germany
¹⁴ Max Planck Institute for Gravitational Physics (Albert Einstein Institute), 30167 Hannover, Germany
¹⁵ Leibniz Universität Hannover, 30167 Hannover, Germany
¹⁶ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
¹⁷ National Astronomical Research Institute of Thailand, Don Kaeo, Mae Rim, Chiang Mai 50180, Thailand

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 17 July 2025
Accepted: 16 December 2025

Abstract

Aims. The mysterious Galactic center (GC) gamma-ray (γ-ray) excess (GCE) could be explained by a large population of millisecond pulsars (MSPs) hiding in the Galactic bulge, too faint to be detected as individual high-energy point sources by the Fermi Large Area Telescope and too fast and dispersed to be detected in shallow radio pulsation surveys.

Methods. Motivated by an innovative candidate selection method, we aim to detect millisecond pulsars associated with the GCE by carrying out deep radio pulsation searches toward promising candidates detected in the inner Galaxy in X rays by Chandra and in radio or γ rays by the Very Large Array or Fermi.

Results. We conducted deep radio observation and follow-up campaigns with MeerKAT, as well as the Murriyang and Green Bank telescopes toward nine X-ray candidate sources.

Conclusions. We report the detection of two new MSPs, including a black widow candidate, toward the Galactic bulge: PSRs J1740-2805 and J1740-28. These discoveries double the number of MSPs discovered within the innermost 2° from the GC.