Research On The Evolution Of Millisecond Pulsar Profile Width With Frequency

Pulsars,a compact object discovered in the 1960s,are generally considered to be fast-spinning neutron stars or quark stars.The radiation widths of slow-turning normal pulsars have been studied with large samples,but there are few studies on millisecond pulsars.The first part of this paper is to screen 38 millisecond pulsars from the EPN database and measure the 10%peak width of the pulsar contours.The Thorsett relation is used to fit the data,and the relative variation rates of the widths of each pulsar at 400 MHz and 4.85 GHz are obtained.The results show that 48%of the millisecond pulsar profiles narrow with the increase of frequency,13%of the profiles remain basically unchanged with the increase of frequency,and 39%of the profiles broaden obviously at high frequencies.This result is similar to that,but the ratio of the width to the width of normal pulsars is significantly higher than that of normal pulsars.Kramer et al.have proposed a geometrical effect that the radio spectrum of pulsars could be steeper than the intrinsic one if the part in the emission beam swept by our line of sight get closer to the edge.With 78 pulsars with known inclination and impact angles,the relationship between pulse width and frequency,and the spectral index collected from literature,the distribution of the spectral index versus the fraction between the impact angle and the beam width was investigated in the second part of this paper.No correlation between these two parameters was found,therefore,this geometric effect inducing steeper spectra can be ruled out statistically.Our result will be helpful for the futher research of emission beam,frequency dependence of pulse width,emission mechanism.