The Effective Magnetic Field Decay of Radio Pulsars: Insights from the Statistical Properties of Their Spin Frequency's Second Derivatives

We present a new method to investigate the effective magnetic field decay of isolated neutron stars, from the analysis of the long-term timing data of a large sample of radio pulsars. There are some differences between the distributions of frequency's second derivatives of the pulsar spins with different effective field decay timescales. Kolmogorov-Smirnov tests are performed to reexamine the consistency of distributions of the simulated and reported data for a series of values of decay timescales. We show that the timescale of the effective field decay exceeds similar to 5 Myr for pulsars with spindown age tau(C)< 10(7) yr or similar to 100 Myr for pulsars with 10(7) < tau(C) < 10(9) yr in the sample. The result does not depend on any specific theories of the field evolution, the inclination decay, or the variation in the moment of inertia. It is also found that the extent of the closed-line region of the magnetic field is close to the light cylinder r(1c), i.e., the corotating radius r(c) approximate to r(1c) is a good approximation for the observed pulsar population.