Speaker
Description
We studied accretion torque induced change in the pulse period derivative of the X-ray binary pulsar A 0535+262 using the long-term light curve from the MAXI/GSC and the time variation of the pulse period from the Fermi/GBM. We found a clear anti-correlation between the bolometric luminosity and the period derivative. We applied the accretion torque model proposed by Ghosh and Lamb (1979) to the observed anti-correlation. This model predicts the relation between the luminosity and the period derivative considering the fundamental parameters of the system including the mass and radius of the neutron star, and hence the application of the model to the data enables us to constrain these parameters. From the A 0535+262 data, we obtained a neutron star mass of 1.1-1.2 solar mass. In this presentation, we will present the details of the analysis and results and discuss possible uncertainties in the results produced by the model and the data.
