arXiv subjects

Mengmeng Ni

Publications and source records attributed to Mengmeng Ni.

4 recordsLinked to original sources

arXiv2026

A pulsar escaping an ancient open cluster via tidal stripping

Open clusters are the primary birthplaces of stars in the Milky Way disk, yet their neutron star progeny are rarely found within them, presumably due to supernova-induced kicks that eject them at birth. Here we report the arcsec-level localization of the pulsar PSR J1921+3745 to the tidal tail of NGC 6791, one of the oldest and most massive open clusters. Our N-body simulation shows that more than 95% of neutron stars formed in such clusters have been ejected. This pulsar's location in the tidal tail indicates it was retained for billions of years before being stripped by Galactic tides. This long-term retention requires low natal kicks, consistent with formation via electron-capture supernova. Our findings capture a rare snapshot of a neutron star transitioning into the Galactic field, identifying tidal stripping of ancient clusters as a verified source of the Galactic neutron star population.

astro-ph.HE↗

arXiv2026

Discovery of a millisecond pulsar with a CO white dwarf companion

We report the discovery and characterization of PSR J1810-0623, a fully recycled millisecond pulsar with a spin period of 4.55 ms, discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and followed up with FAST and the Green Bank Telescope (GBT). A phase-connected timing solution spanning over 6.5 years reveals a 15.4-day binary orbit with extremely low eccentricity (about 1.5E-5). Assuming a neutron star mass of 1.4 Msun, the inferred companion median mass (about 0.64 Msun) is consistent with a carbon-oxygen white dwarf, indicating an evolutionary origin in an intermediate mass Xray binary. The system's properties closely resemble those of other massive white dwarf binaries thought to form via Case A Roche lobe overflow, suggesting a prolonged accretion phase during which the neutron star was efficiently recycled. Polarimetric analysis of FAST data yields a moderate degree of linear polarization and a rotation measure of 86.6 pm 0.6 rad/m^2, offering constraints on the Galactic magnetic field. The inferred characteristic age (about 32 Gyr) and low surface magnetic field (about 1E8 G) indicate a highly recycled pulsar. Proper-motion measurements imply a modest transverse velocity, consistent with those of recycled millisecond pulsars in the Galactic field. Although the proximity of the globular cluster Pal 7 raises the possibility of a dynamical origin, discrepancies in dispersion measure and proper motion argue against a physical association. PSR J1810-0623 adds to the rare class of long-orbital period MSP-COWD systems and provides a valuable laboratory for studying pulsar recycling, binary evolution, and Galactic structure.

astro-ph.HE↗

arXiv2023

Discovery and Timing of Millisecond Pulsars in the Globular Cluster M5 (NGC 5904) with FAST and Arecibo

We report on a comprehensive multi-wavelength study of the pulsars in the globular cluster (GC) M5, including the discovery of M5G, a new compact non-eclipsing "black widow" pulsar. Thanks to the analysis of 34 years of radio data taken with the FAST and Arecibo telescopes, we obtained new phase-connected timing solutions for four pulsars in the clusters and improved those of the other three known pulsars. These have resulted in, among other things: a) much improved proper motions for five pulsars, with transverse velocities that are smaller than their respective escape velocities; b) 3-sigma and 1.5-sigma detections of Shapiro delays in M5F and M5D, respectively; c) greatly improved measurement of the periastron advance in M5B, whose value of 0.01361(6) implies that M5B is still likely to be a heavy neutron star. The binary pulsars M5D, E and F are confirmed to be in low-eccentricity binary systems, the low-mass companions of which are newly identified to be He white dwarfs using Hubble Space Telescope data. Four pulsars are also found to be associated with X-ray sources. Similarly to the eclipsing pulsar M5C, M5G shows little or no non-thermal X-ray emission, indicative of weak synchrotron radiation produced by intra-binary shocks. All the seven pulsars known in M5 have short spin periods and five are in binary systems with low orbital eccentricities. These characteristics differ from the overall GC pulsar population, but confirm the expectations for the pulsar population in a cluster with a small rate of stellar encounters per binary system.

astro-ph.HE↗

arXiv2022

Radio detection of an elusive millisecond pulsar in the Globular Cluster NGC 6397

We report the discovery of a new 5.78 ms-period millisecond pulsar (MSP), PSR J1740-5340B (NGC 6397B), in an eclipsing binary system discovered with the Parkes radio telescope (now also known as Murriyang), Australia, and confirmed with the MeerKAT radio telescope in South Africa. The measured orbital period, 1.97 days, is the longest among all eclipsing binaries in globular clusters (GCs) and consistent with that of the coincident X-ray source U18, previously suggested to be a 'hidden MSP'. Our XMM-Newton observations during NGC 6397B's radio quiescent epochs detected no X-ray flares. NGC 6397B is either a transitional MSP or an eclipsing binary in its initial stage of mass transfer after the companion star left the main sequence. The discovery of NGC 6397B potentially reveals a subgroup of extremely faint and heavily obscured binary pulsars, thus providing a plausible explanation to the apparent dearth of binary neutron stars in core-collapsed GCs as well as a critical constraint on the evolution of GCs.

astro-ph.HE↗