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 comple- menting historical measurements with the data from the gamma-ray burst monitor onboard Fermi obtained during the outburst in June-October 2015. We model the observed changes in the spin- frequency of the pulsar and deduce the orbital parameters of the system. We significantly improve existing constrains and show that contrary to the 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 previosly observed values and predictions of the accretion torque theory.