Black hole-like hysteresis and accretion states in neutron star low-mass X-ray binaries

Muñoz-Darias, T.; Fender, R. P.; Motta, S.; Belloni, T.

doi:10.1093/mnras/stu1334

Cited by 142 publications

(155 citation statements)

References 75 publications

(77 reference statements)

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“…Comparing the state classification defined by Muñoz-Darias et al (2014) and the X-ray colour analysis reported by Kajava et al (2014) for 4U 1636-536, 4U 1608-52, and 4U 1728-34, we found that for a few bursts the two methods resulted in ambiguous classifications (particularly for 4U 1636-536), and in those cases we adjusted the limits so that both colour and rms diagrams had the least ambiguities. We also find that (see Fig.…”

Section: Muñozmentioning

confidence: 88%

“…Galloway et al 1 See also http://burst.sci.monash.edu/sources and https://personal.sron.nl/ jeanz/bursterlist.html 2008; Kajava et al 2014, and references therein). Many bursting NSs in LXMBs alternate between so-called hard and soft spectral states (Muñoz-Darias et al 2014), and X-ray bursts can occur while the LMXB is in either of those two states or during state transitions (i.e. the intermediate state).…”

Section: Introductionmentioning

confidence: 99%

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Flux decay during thermonuclear X-ray bursts analysed with the dynamic power-law index method

Kuuttila

Kajava

Nättilä

et al. 2017

A&A

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The cooling of type-I X-ray bursts can be used to probe the nuclear burning conditions in neutron star envelopes. The flux decay of the bursts has been traditionally modelled with an exponential, even if theoretical considerations predict power-law-like decays. We have analysed a total of 540 type-I X-ray bursts from five low-mass X-ray binaries observed with the Rossi X-ray Timing Explorer. We grouped the bursts according to the source spectral state during which they were observed (hard or soft), flagging those bursts that showed signs of photospheric radius expansion (PRE). The decay phase of all the bursts were then fitted with a dynamic power-law index method. This method provides a new way of probing the chemical composition of the accreted material. Our results show that in the hydrogen-rich sources the power-law decay index is variable during the burst tails and that simple cooling models qualitatively describe the cooling of presumably helium-rich sources 4U 1728-34 and 3A 1820-303. The cooling in the hydrogen-rich sources 4U 1608-52, 4U 1636-536, and GS 1826-24, instead, is clearly different and depends on the spectral states and whether PRE occurred or not. Especially the hard state bursts behave differently than the models predict, exhibiting a peculiar rise in the cooling index at low burst fluxes, which suggests that the cooling in the tail is much faster than expected. Our results indicate that the drivers of the bursting behaviour are not only the accretion rate and chemical composition of the accreted material, but also the cooling that is somehow linked to the spectral states. The latter suggests that the properties of the burning layers deep in the neutron star envelope might be impacted differently depending on the spectral state.

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Section: Muñozmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Flux decay during thermonuclear X-ray bursts analysed with the dynamic power-law index method

Kuuttila

Kajava

Nättilä

et al. 2017

A&A

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“…The neutron star spin frequency is measured to be about 363 Hz from X-ray burst oscillations (Strohmayer et al 1996). RXTE/PCA observations have shown that 4U 1728-34 undergoes the typical hysteresis pattern between hard and soft spectral states (e.g., Muñoz-Darias et al 2014). In the hard state the X-ray bursts are almost exclusively Eddingtonlimited photospheric radius expansion bursts (Galloway et al 2008;Zhang et al 2016), although the peak fluxes show a weak dependency with the properties of the persistent emission (Galloway et al 2003).…”

Section: Observations and Data Analysismentioning

confidence: 99%

X-ray burst-induced spectral variability in 4U 1728–34

Kajava

Sánchez–Fernández

Kuulkers

et al. 2017

A&A

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Aims. INTEGRAL has been monitoring the Galactic center region for more than a decade. Over this time INTEGRAL has detected hundreds of type-I X-ray bursts from the neutron star low-mass X-ray binary 4U 1728-34, a.k.a. "the slow burster". Our aim is to study the connection between the persistent X-ray spectra and the X-ray burst spectra in a broad spectral range. Methods. We performed spectral modeling of the persistent emission and the X-ray burst emission of 4U 1728-34 using data from the INTEGRAL JEM-X and IBIS/ISGRI instruments. Results. We constructed a hardness intensity diagram to track spectral state variations. In the soft state the energy spectra are characterized by two thermal components -likely from the accretion disc and the boundary/spreading layer -together with a weak hard X-ray tail that we detect in 4U 1728-34 for the first time in the ∼40 to 80 keV range. In the hard state the source is detected up to ∼200 keV and the spectrum can be described by a thermal Comptonization model plus an additional component: either a powerlaw tail or reflection. By stacking 123 X-ray bursts in the hard state, we detect emission up to 80 keV during the X-ray bursts. We find that during the bursts the emission above 40 keV decreases by a factor of about three with respect to the persistent emission level. Conclusions. Our results suggest that the enhanced X-ray burst emission changes the spectral properties of the accretion disc in the hard state. The likely cause is an X-ray burst induced cooling of the electrons in the inner hot flow near the neutron star.

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“…Because the mass-to-radius ratio in neutron stars and black holes is similar 1 , the characteristic velocities and dynamical time scales near the compact object are also similar (v ∼ 0.5c, t < ∼ 1 ms). Thus, it is not surprising that BHXB and NSXB show very similar X-ray spectral and temporal characteristics (van der Klis 1994Klis , 2005Maccarone & Coppi 2003;Barret 2004;Di Salvo et al 2006;Muñoz-Darias et al 2014).…”

Section: Introductionmentioning

confidence: 99%

The origin of the hard X-ray tail in neutron-star X-ray binaries

Reig

Kylafis

2016

A&A

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Context. Neutron star X-ray binaries emit a compact, optically thick, relativistic radio jet during low-luminosity, usually hard states, as Galactic black-hole X-ray binaries do. When radio emission is bright, a hard power-law tail without evidence for an exponential cutoff is observed in most systems. Aims. We have developed a jet model that explains many spectral and timing properties of black-hole binaries in the states where a jet is present. Our goal is to investigate whether our jet model can reproduce the hard tail, with the correct range of photon index and the absence of a high-energy cutoff, in neutron-star X-ray binaries. Methods. We performed Monte Carlo simulations of the Compton upscattering of soft, accretion-disk or boundary layer photons in the jet and computed the emergent energy spectra, as well as the time lag of hard photons with respect to softer ones as a function of Fourier frequency. We fit the energy spectra with a power law modified by an exponential cutoff at high energy. Results. We demonstrate that our jet model naturally explains the observed power-law distribution with photon index in the range 1.8-3. With an appropriate choice of the parameters, the cutoff expected from Comptonization is shifted to energies above ∼300 keV, producing a pure power law without any evidence for a rollover, in agreement with the observations. Conclusions. Our results reinforce the idea that the link between the outflow (jet) and inflow (disk) in X-ray binaries does not depend on the nature of the compact object, but on the process of accretion. Furthermore, we address the differences between jets in black-hole and neutron-star X-ray binaries and predict that the break frequency in the spectral energy distribution of neutron-star X-ray binaries, as a class, will be lower than that of black-hole binaries.

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Black hole-like hysteresis and accretion states in neutron star low-mass X-ray binaries

Cited by 142 publications

References 75 publications

Flux decay during thermonuclear X-ray bursts analysed with the dynamic power-law index method

Flux decay during thermonuclear X-ray bursts analysed with the dynamic power-law index method

X-ray burst-induced spectral variability in 4U 1728–34

The origin of the hard X-ray tail in neutron-star X-ray binaries

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