On the curious pulsation properties of the accreting millisecond pulsar IGR J17379-3747

Abstract

We report on the Neutron Star Interior Composition Explorer (NICER) monitoring campaign of the 468 Hz accreting millisecond X-ray pulsar IGR J17379-3747. From a detailed spectral and timing analysis of the coherent pulsations we find that they show a strong energy dependence, with soft thermal emission lagging about 640 microseconds behind the hard, Comptonized emission. Additionally, we observe uncommonly large pulse fractions, with measured amplitudes in excess of 20% sinusoidal fractional amplitude across the NICER passband and fluctuations of up to ~70%. Based on a phase-resolved spectral analysis, we suggest that these extreme properties might be explained if the source has an unusually favorable viewing geometry with a large magnetic misalignment angle. Due to these large pulse fractions, we were able to detect pulsations down to quiescent luminosities (~5 x 10^33 erg s^-1). We discuss these low-luminosity pulsations in the context of transitional millisecond pulsars.

16 pages, 8 figures, 3 tables. Accepted for publication in ApJ

References in corpus (15)

• TEMPO2, a new pulsar timing package. I: Overview
• The 3rd IBIS/ISGRI soft gamma-ray survey catalog
• INTEGRAL/IBIS all-sky survey in hard X-rays
• The hard X-ray spectral evolution in X-ray binaries and its application to constrain the black hole mass of ultraluminous X-ray sources
• NuSTAR J095551+6940.8: a highly magnetised neutron star with super-Eddington mass accretion
• The Variable Quiescent X-ray Emission of the Neutron Star Transient XTE J1701-462
• Models of AM CVn star outbursts
• Neutron star crust cooling in KS 1731-260: the influence of accretion outburst variability on the crustal temperature evolution
• Spectral and timing properties of IGR J00291+5934 during its 2015 outburst
• Spectral and timing properties of the accreting X-ray millisecond pulsar IGR J17498-2921
• Hard X-ray Bursts Detected by the IBIS Telescope Onboard the INTEGRAL Observatory in 2003-2004
• Precise Orbital Parameters and Anomalous Phase Variations of the Accretion-powered Millisecond Pulsar XTE J1807-294
• The aperiodic X-ray variability of the accreting millisecond pulsar SAX J1808.4-3658
• Spectral Softening Between Outburst and Quiescence In The Neutron Star Low-Mass X-Ray Binary SAX J1750.8-2900
• Discovery of 1-5 Hz flaring at high luminosity in SAX J1808.4-3658

Cited by in corpus (8)

• Search for continuous gravitational waves from 20 accreting millisecond X-ray pulsars in O3 LIGO data
• Low-Mass X-ray Binaries
• A NICER look at the state transitions of the black hole candidate MAXI J1535-571 during its reflares
• Variability and phase lags of the type-C quasi-periodic oscillation of MAXI J1348-630 with NICER
• The radiative efficiency of neutron stars at low-level accretion
• Detection of low-luminosity X-ray pulsations from the accreting millisecond pulsar IGR J17511-3057: An ever-thinning thread between bright accretion and sub-luminous states
• Updated Spin and Orbital Parameters and Energy Dependent Pulse Behaviors of the Accreting Millisecond X-ray Pulsar IGR J17591$-$2342
• The 2025 outburst of IGR J17511-3057: timing and spectral insights from NICER and NuSTAR