The youngest white dwarf companion to a millisecond pulsar: Insights from NGC 362D
arXiv:2609.05608
Abstract
We report on the identification of the optical counterpart to the recently discovered millisecond pulsar (MSP) NGC362D in the Galactic globular cluster NGC362 based on deep, multi-band, and multi-epoch Hubble Space Telescope observations. Our analysis robustly shows that this object is a very low-mass () He white dwarf (WD) still in the pre-cooling phase. Interestingly, a detailed comparison with updated binary evolution models indicates that this object completed the mass-transfer phase only recently ( Gyr ago), thus strongly suggesting that COM-NGC362D is the youngest WD companion to a MSP identified to date. Remarkably, in this respect, the photometric properties of NGC362D show, for the first time in this class of objects, significant wavelength-dependent variations that are consistent with the presence of residual circumstellar material. This system therefore provides a valuable test case to directly probe the immediate aftermath of the MSP recycling process and to constrain the early evolutionary stages of proto-WD companions and their radio and optical properties. Our results suggest that residual material can produce radio and optical signatures that mimic those of systems with non-degenerate companions, potentially leading to the misclassification of young MSPs.
Accepted for publication in Astronomy and Astrophysics Letters. 4 pages, 2 figures (additional 4 pages and 6 figures in the Appendix)