Orbital parameters of V 0332+53 from 2015 giant outburst data

Abstract

We present the updated orbital solution for the transient Be X-ray binary V 0332+53, which we obtained by complementing historical measurements with the data from the gamma-ray burst monitor onboard Fermi. These were acquired during the outburst in June-October 2015. We modeled the observed changes in the spin-frequency of the pulsar and deduced the orbital parameters of the system. We significantly improved existing constrains and show that contrary to previous findings, no change in orbital parameters is required to explain the spin evolution of the source during the outbursts in 1983, 2005, and 2015. The reconstructed intrinsic spin-up of the neutron star during the latest outburst is found to be comparable with previously observed values and predictions of the accretion torque theory.