The GMRT High-resolution Southern Sky Survey for Pulsars and Transients. VIII. Orbital Variability and the Evolution of a 1 day He-WD Millisecond Pulsar J2101–4802

Abstract

Abstract We present timing and orbital phase-resolved polarimetry of the millisecond pulsar (MSP) J2101−4802, having a spin period of 9.48 ms and dispersion measure (DM) 25.05 pc cm −3 discovered with the Giant Meter Radio Telescope (GMRT). From the phase-connected timing of this MSP spanning 3.7 yr, we identify that PSR J2101–4802 is in a ∼1 day binary orbit with a likely helium-white-dwarf (He-WD) companion having a median companion mass ≃0.15 M ⊙ (assuming the inclination angle 60°), consistent with canonical recycling in the Galactic field. The timing solution further reveals an unusually large orbital period derivative, P ̇ b (∼10 −11 s s −1 ), compared to typical Galactic-field MSP–HeWD binaries, which cannot be explained by the contributions from kinematic effects (Shklovskii and Galactic acceleration) or general-relativistic damping. Using wideband, full-Stokes observations, we also trace the linear and circular polarization variation across the orbital phase and fit a rotating-vector model (RVM) to its position-angle swing across orbital phase, yielding constraints on the emission geometry (magnetic inclination and impact angle) of this system. The combination of a ∼1 day orbit, ∼0.15 M ⊙ companion, modest spin-down power, unusually large P ̇ b , and phase-locked magnetized intrabinary plasma signatures suggests that PSR J2101−4802 represent a transitional system linking redback-like spiders to detached He-WD MSP binaries.