Timing of the accreting millisecond pulsar IGR J17591-2342: evidence of spin-down during accretion

Abstract

We report on the phase-coherent timing analysis of the accreting millisecond X-ray pulsar IGR J17591-2342, using Neutron Star Interior Composition Explorer (NICER) data taken during the outburst of the source between 2018 August 15 and 2018 October 17. We obtain an updated orbital solution of the binary system. We investigate the evolution of the neutron star spin frequency during the outburst, reporting a refined estimate of the spin frequency and the first estimate of the spin frequency derivative ($\dot{\nu }\sim -7\times 10^{-14}$ Hz s${}^{-1}$), confirmed independently from the modelling of the fundamental frequency and its first harmonic. We further investigate the evolution of the X-ray pulse phases adopting a physical model that accounts for the accretion material torque as well as the magnetic threading of the accretion disc in regions where the Keplerian velocity is slower than the magnetosphere velocity. From this analysis we estimate the neutron star magnetic field $B_{eq}=2.8(3)\times 10^8$ G. Finally, we investigate the pulse profile dependence on energy finding that the observed behaviour of the pulse fractional amplitude and lags as a function of energy are compatible with a thermal Comptonisation of the soft photons emitted from the neutron star caps.

Submitted to MNRAS. 10 pages, 6 figures, 2 tables

References in corpus (10)

• Discovery of coherent millisecond X-ray pulsations in Aql X-1
• Timing of the Accreting Millisecond Pulsar XTE J1814-338
• Order in the Chaos: Spin-up and Spin-down during the 2002 Outburst of SAX J1808.4-3658
• Phase-coherent timing of the accreting millisecond pulsar SAX J1748.9-2021
• Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934
• On the timing properties of SAX J1808.4-3658 during its 2015 outburst
• Spectral and timing properties of the accreting X-ray millisecond pulsar IGR J17511-3057
• Spin up and phase fluctuations in the timing of the accreting millisecond pulsar XTE J1807-294
• Spectral and timing properties of IGR J00291+5934 during its 2015 outburst
• High-energy characteristics of the accretion-powered millisecond pulsar IGR J17591-2342 during its 2018 outburst

Cited by in corpus (10)

• Search for continuous gravitational waves from 20 accreting millisecond X-ray pulsars in O3 LIGO data
• The discovery of the 528.6 Hz accreting millisecond X-ray pulsar MAXI J1816-195
• The AstroSat observation of accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst
• Broadband X-ray timing and spectral characteristics of the accretion-powered millisecond X-ray pulsar MAXI J1816$-$195
• Spectral analysis of the AMXP IGR J17591-2342 during its 2018 outburst
• AstroSat timing and spectral analysis of the accretion-powered millisecond X-ray pulsar IGR J17591--2342
• The spin-down accretion regime of Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124
• An unusual type-I X-ray burst from the neutron star X-ray binary IGR J17591-2342: a double-photospheric-radius-expansion burst?
• The 2025 outburst of IGR J17511-3057: timing and spectral insights from NICER and NuSTAR
• Rapid Orbital Decay in the Ultracompact Double-degenerate Binary eRASSU J060839.5$-$704014