X-ray variability of transitional millisecond pulsars: a faint, stable and fluctuating disk

Abstract

Transitional millisecond pulsars (tMSPs) have emerged in the last decade as a unique class of neutron stars at the crossroads between accretion- and rotation-powered phenomena. In their (sub-luminous) accretion disk state, with X-ray luminosities of order $10^{33}-10^{34}$ erg s${}^{-1}$, they switch rapidly between two distinct X-ray modes: the disk-high (DH) and disk-low (DL) states. We present a systematic XMM-Newton and Chandra analysis of the aperiodic X-ray variability of all three currently known tMSPs, with a main focus on their disk state and separating DH and DL modes. We report the discovery of flat-topped broadband noise in the DH state of two of them, with break frequencies of 2.8 mHz (PSR J1023+0038) and 0.86 mHz (M28-I). We argue that the lowest frequency variability is similar to that seen in disk-accreting X-ray binaries in the hard state, at typical luminosities at least 2 orders of magnitude higher than tMSPs. We find strong variability in the DH state around 1 Hz, not typical of hard state X-ray binaries, with fractional rms amplitudes close to 30%. We discuss our results and use them to constrain the properties of the accretion disk, assuming that the X-ray variability is produced by fluctuations in mass accretion rate, and that the break frequency corresponds to the viscous timescale at the inner edge of the disk. In this context, we find that the newly found break frequencies are broadly consistent with a disk truncated close to the light cylinder with $\dot{M}\simeq 10^{13}-5\times 10^{14}$ g s${}^{-1}$ and a viscosity parameter $\alpha \gtrsim$0.2.

arXiv commentMNRAS, accepted. 10 pages, 7 figures, 2 tables

References in corpus (34)

• A Radio Pulsar/X-ray Binary Link
• Accretion disc viscosity: how big is alpha?
• Swings between rotation and accretion power in a millisecond binary pulsar
• BlackCAT: A catalogue of stellar-mass black holes in X-ray transients
• The broad-band power spectra of X-ray binaries
• Re-examining the X-Ray versus Spin-Down Luminosity Correlation of Rotation Powered Pulsars
• A state change in the low-mass X-ray binary XSS J12270-4859
• Discovery of PSR J1227-4853: A transition from a low-mass X-ray binary to a redback millisecond pulsar
• An exact analytic treatment of propagating mass accretion rate fluctuations in X-ray binaries
• Modelling variability in black hole binaries: linking simulations to observations
• A Chandra X-ray Observation of the Binary Millisecond Pulsar PSR J1023+0038
• Surrounded by Spiders! New Black Widows and Redbacks in the Galactic Field
• A parallax distance and mass estimate for the transitional millisecond pulsar system J1023+0038
• X-ray follow-ups of XSSJ12270-4859: a low-mass X-ray binary with gamma ray FERMI-LAT association
• Strong disc winds traced throughout outbursts in black-hole X-ray binaries
• Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar B1821-24
• X-ray coherent pulsations during a sub-luminous accretion disk state of the transitional millisecond pulsar XSS J12270-4859
• X-ray states of redback millisecond pulsars
• Optical pulsations from a transitional millisecond pulsar
• The neutron star transient and millisecond pulsar in M28: from sub-luminous accretion to rotation-powered quiescence
• Identification of the High-Energy Gamma-Ray Source 3FGL J1544.6-1125 as a Transitional Millisecond Pulsar Binary in an Accreting State
• Detection of Low-Hard State Spectral and Timing Signatures from the Black Hole X-Ray Transient XTE J1650-500 at Low X-Ray Luminosities
• NuSTAR Observations of the State Transition of Millisecond Pulsar Binary PSR J1023+0038
• Pulsating in unison at optical and X-ray energies: simultaneous high-time resolution observations of the transitional millisecond pulsar PSR J1023+0038
• A propeller scenario for the gamma-ray emission of low-mass X-ray binaries: The case of XSS J12270-4859
• Engulfing a radio pulsar: the case of PSR J1023+0038
• "Hiccup" accretion in the swinging pulsar IGR J18245-2452
• A physical scenario for the high and low X-ray luminosity states in the transitional pulsar PSR J1023+0038
• Disks Surviving the Radiation Pressure of Radio Pulsars
• Pulsar wind-heated accretion disk and the origin of modes in transitional millisecond pulsar PSR J1023+0038
• Prolonged sub-luminous state of the new transitional pulsar candidate CXOU J110926.4-650224
• An accreting millisecond pulsar with black hole-like X-ray variability: IGR J00291+5934
• Rapid X-ray variability properties during the unusual very hard state in neutron-star low-mass X-ray binaries
• The binary millisecond pulsar PSR J1023+0038 -- II. Optical spectroscopy

Cited by in corpus (4)

• Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038
• Multiwavelength Evidence for Two New Candidate Transitional Millisecond Pulsars in the Sub-luminous Disk State: 4FGL J0639.1--8009 and 4FGL J1824.2+1231
• Polarized multiwavelength emission from pulsar wind - accretion disk interaction in a transitional millisecond pulsar
• Hydrodynamical simulations of wind interaction in spider systems : A step toward understanding transitional millisecond pulsars