2025ApJ...991..135G

Pulse profile stability in millisecond pulsars (MSPs) is a key factor in achieving high-precision timing essential for detecting nanohertz gravitational waves with pulsar timing arrays (PTAs). In this work, we present a systematic analysis of profile stabilization timescales in MSPs using a direct method based on pulse stacking, applied to long-term multiepoch observations. Our study utilizes data from the upgraded Giant Metrewave Radio Telescope (uGMRT) between 300 and 750 MHz for nine MSPs over 3-5 yr and Parkes Ultra-Wideband, low-frequency receiver observations (covering 704-4032 MHz) for three of them. We find that stable profiles typically require averaging over 10⁵-10⁶ pulses. This is the first time such a quantitative approach has been applied to MSPs across a wide frequency range, providing an indirect but practical estimate of jitter noise-a dominant noise source in PTA data sets. We observe that stabilization timescales depend on signal-to-noise ratio, pulse morphology, and surface magnetic field strength, with a moderate correlation indicating a possible role of magnetic field in emission stability. A complementary single-epoch analysis of nine bright MSPs with uGMRT Band-3 (300-500 MHz) reinforces these results and demonstrates the method's applicability to broader MSP populations. We show that a strong correlation exists between profile-stability slope and the jitter parameter, implying that, for faint MSPs, profile-stability analysis can act as an effective proxy for intrinsic pulse-shape variability. Our work provides a novel and scalable framework to assess intrinsic profile variability, helping to guide integration time choices and reduce timing noise in PTA experiments.