Broad-band aperiodic variability in X-ray pulsars: accretion rate fluctuations propagating under the influence of viscous diffusion

Mushtukov, Alexander A.; Lipunova, G. V.; Ingram, Adam; Tsygankov, Sergey S.; Mönkkönen, Juhani; Klis, M. van der

doi:10.1093/mnras/stz948

Cited by 27 publications

(21 citation statements)

References 74 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This was later confirmed by the simulations of Hogg & Reynolds (2016) and may be related to what we are seeing here. A similar break, happening below the local Keplerian frequency, has recently been inferred from X-ray pulsar data (Mushtukov et al 2019).…”

Section: Power Spectrasupporting

confidence: 75%

Looking for the underlying cause of black hole X-ray variability in GRMHD simulations

Bollimpalli

Mahmoud

Done

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

ABSTRACT Long-term observations have shown that black hole X-ray binaries exhibit strong, aperiodic variability on time-scales of a few milliseconds to seconds. The observed light curves display various characteristic features like a lognormal distribution of flux and a linear rms–flux relation, which indicate that the underlying variability process is stochastic in nature. It is also thought to be intrinsic to accretion. This variability has been modelled as inward propagating fluctuations of mass accretion rate, although the physical process driving the fluctuations remains puzzling. In this work, we analyse five exceptionally long-duration general relativistic magnetohydrodynamic (GRMHD) simulations of optically thin, geometrically thick, black hole accretion flows to look for hints of propagating fluctuations in the simulation data. We find that the accretion profiles from these simulations do show evidence for inward propagating fluctuations below the viscous frequency by featuring strong radial coherence and positive time lags when comparing smaller to larger radii, although these time lags are generally shorter than the viscous time-scale and are frequency-independent. Our simulations also support the notion that the fluctuations in $\dot{M}$ build up in a multiplicative manner, as the simulations exhibit linear rms–mass flux relations, as well as lognormal distributions of their mass fluxes. When combining the mass fluxes from the simulations with an assumed emissivity profile, we additionally find broad agreement with observed power spectra and time lags, including a recovery of the frequency dependency of the time lags.

show abstract

Section: Power Spectrasupporting

confidence: 75%

Looking for the underlying cause of black hole X-ray variability in GRMHD simulations

Bollimpalli

Mahmoud

Done

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…Thus XMMU J051342.6−672412 would not reach the current spin period of 4.4 s if it was born at typical birth periods of less than one second (if XMMU J051342.6−672412 was born near its current period, the propeller timescale at these weak fields is longer than the current age; see discussion in Section 3). A time-varying accretion rate (see, e.g., Tauris et al 2012;Bhattacharyya & Chakrabarty 2017;D'Angelo 2017;Mushtukov et al 2019) might yield a solution such that XMMU J051342.6−672412 is in the accretor phase and have a weak field, but this would require fine-tuning. For example, a very high accretion rate at early times could cause cessation of the ejector phase, but this would also shorten the propeller phase such that the accretor/spin equilibrium phase would begin at much shorter periods than the current spin period.…”

Section: Discussionmentioning

confidence: 99%

Early neutron star evolution in high-mass X-ray binaries

Wijngaarden

Andersson

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

The application of standard accretion theory to observations of X-ray binaries provides valuable insights into neutron star properties, such as their spin period and magnetic field. However, most studies concentrate on relatively old systems, where the neutron star is in its late propeller, accretor, or nearly spin equilibrium phase. Here we use an analytic model from standard accretion theory to illustrate the evolution of high-mass X-ray binaries early in their life. We show that a young neutron star is unlikely to be an accretor because of the long duration of ejector and propeller phases. We apply the model to the recently discovered ∼ 4000 yr old high-mass X-ray binary XMMU J051342.6−672412 and find that the system's neutron star, with a tentative spin period of 4.4 s, cannot be in the accretor phase and has a magnetic field B > a few × 10 13 G, which is comparable to the magnetic field of many older high-mass X-ray binaries and is much higher than the spin equilibrium inferred value of a few × 10 11 G. The observed X-ray luminosity could be the result of thermal emission from a young cooling magnetic neutron star or a small amount of accretion that can occur in the propeller phase.

show abstract

“…δt is the time resolution of the light curve. Because the variability of accreting X-ray pulsars at high frequencies is strongly suppressed (Reig & Nespoli 2013), most likely due to the viscous diffusion associated to accretion rate fluctuations (Mushtukov et al 2019), the time resolution need not be too small. We set the highest frequency at 16 Hz (δt = 0.03125 s).…”

Section: Broad-band Noisementioning

confidence: 99%

“…The second approach is to use a broken power law model. Because many accreting pulsars displays breaks in their power spectra (Revnivtsev et al 2009;Mushtukov et al 2019), the broken or double broken power law model has been used successfully in broad-band noise analysis (Doroshenko et al 2014(Doroshenko et al , 2020. The model parameters of a broken power law are, in addition to the normalization, the break frequency, ν break and two power low indices, Γ 1 , Γ 2 .…”

Section: Broad-band Noisementioning

confidence: 99%

“…The slowest time scales are linked to the mass transfer process between the Be star and the neutron star and manifest as unpredictable giant (or type II) Xray outbursts on time scales of years. Time scales attributed to the accretion process vary in the range from fraction of a second to hours and manifest as broad-band noise in the power spectrum (Revnivtsev et al 2009;Mushtukov et al 2019). In addition, quasi-periodic oscillations (QPO) in the millihertz range are commonly detected (James et al 2010).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

X-ray spectral-timing variability of 1A 0535+262 during the 2020 giant outburst

Reig,

Ma,

Tao

et al. 2021

Preprint

View full text Add to dashboard Cite

Context. The Be/X-ray binary 1A 0535+262 underwent a giant X-ray outburst in November 2020, peaking at ∼ 1 × 10 38 erg s −1 (1-100 keV, 1.8 kpc), the brightest outburst recorded for this source so far. The source was monitored over two orders of magnitude in luminosity with Insight-HXMT, which allowed us to probe the X-ray variability in an unprecented range of accretion rates. Aims. Our goal is to search for patterns of correlated spectral and timing behavior that can be used to characterize the accretion states in hard X-ray transient pulsars.Methods. We have studied the evolution of the spectral continuum emission using hardness-intensity diagrams and the aperiodic variability of the source by analyzing power density spectra. We have used phenomenological models to fit the various broad-band noise components. Results. The hardness-intensity diagram displays three distinct branches that can be identified with different accretion regimes. The characteristic frequency of the noise components correlates with the luminosity. Our observations cover the highest end of this correlation, at luminosities not previously sampled. We have found evidence for a flattening of the correlation at those high luminosities, which might indicate that the accretion disk reached the closest distance from the neutron star surface during the peak of the outburst. We also find evidence for hysteresis in the spectral and timing parameters: at the same luminosity level, the spectrum is harder and the characteristic noise frequency larger during the rise than during the decay of the outburst. Conclusions. As in black hole binaries and low-mass X-ray binaries, the hardness-intensity diagram represents a useful diagnostic tool to define the source state in an accreting pulsar. Our timing analysis confirms previous findings from spectral analysis of a hysteresis pattern of variability where the spectral and timing parameters adopt different values for similar luminosity depending on whether the source is on the rising or decaying phase of the outburst.

show abstract

Broad-band aperiodic variability in X-ray pulsars: accretion rate fluctuations propagating under the influence of viscous diffusion

Cited by 27 publications

References 74 publications

Looking for the underlying cause of black hole X-ray variability in GRMHD simulations

Looking for the underlying cause of black hole X-ray variability in GRMHD simulations

Early neutron star evolution in high-mass X-ray binaries

X-ray spectral-timing variability of 1A 0535+262 during the 2020 giant outburst

Contact Info

Product

Resources

About