The accretion powered spin-up of GRO J1750-27

TL;DR

This study analyzes the spin-up behavior of the pulsar GRO J1750-27 during an outburst, measuring its orbital parameters, intrinsic spin changes, and estimating its distance and magnetic field using X-ray data.

Contribution

The paper provides the first detailed measurement of the intrinsic spin-up and orbital parameters of GRO J1750-27 during a 2008 outburst, and estimates its distance and magnetic field strength.

Findings

Detected intrinsic spin-up with specific Pdot and Pdotdot values.

Estimated the neutron star's magnetic field as ~2E12 G.

Suggested the source is located 12-22 kpc away.

Abstract

The timing properties of the 4.45 s pulsar in the Be X-ray binary system GRO J1750-27 are examined using hard X-ray data from INTEGRAL and Swift during a Type II outburst observed during 2008. The orbital parameters of the system are measured and agree well with those found during the last known outburst of the system in 1995. Correcting the effects of the doppler shifting of the period, due to the orbital motion of the pulsar, leads to the detection of an intrinsic spin-up that is well described by a simple model including Pdot and Pdotdot terms of -7.5E-10 ss^-1 and 1E-16 ss^-2 respectively. The model is then used to compare the time-resolved variation of the X-ray flux and intrinsic spin-up against the accretion torque model of Ghosh & Lamb (1979); this finds that GRO J1750-27 is likely located 12-22 kpc distant and that the surface magnetic field of the neutron star is ~2E12 G. The shape of the pulse and the pulsed fraction shows different behaviour above and below 20 keV indicating that the observed pulsations are the convolution of many complex components.