Cooling of Accretion-Heated Neutron Stars

Wijnands, Rudy; Degenaar, N.; Page, Dany

doi:10.1007/s12036-017-9466-5

Cited by 115 publications

(129 citation statements)

References 193 publications

(181 reference statements)

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“…The origin of this shallow heat source is unknown and is important to resolve because the cooling curve can be used to constrain a number of different aspects of crust physics (such as conductivity of the crust and pasta, and the core specific heat; Brown & Cumming 2009;Horowitz et al 2015;Cumming et al 2017). Most systems need ∼1-2 MeV nucleon −1 of shallow heating to explain their cooling curves (e.g., Degenaar et al 2014;Parikh et al 2017;Wijnands et al 2017). The transient NS LMXB MAXI J0556−332 (hereafter J0556) was discovered on 2011 January 11 (Matsumura et al 2011) and exhibited a ∼16 month outburst.…”

Section: Introductionmentioning

confidence: 99%

Different Accretion Heating of the Neutron Star Crust during Multiple Outbursts in MAXI J0556–332

Parikh

Homan

Wijnands

et al. 2017

ApJL

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The transient neutron star (NS) low-mass X-ray binary MAXI J0556−332 provides a rare opportunity to study NS crust heating and subsequent cooling for multiple outbursts of the same source. We examine MAXI, Swift, Chandra, and XMM-Newton data of MAXI J0556−332 obtained during and after three accretion outbursts of different durations and brightnesses. We report on new data obtained after outburst III. The source has been tracked up to ∼1800 days after the end of outburst I. Outburst I heated the crust strongly, but no significant reheating was observed during outburst II. Cooling from ∼333 eV to ∼146 eV was observed during the first ∼1200 days. Outburst III reheated the crust up to ∼167 eV, after which the crust cooled again to ∼131 eV in ∼350 days. We model the thermal evolution of the crust and find that this source required a different strength and depth of shallow heating during each of the three outbursts. The shallow heating released during outburst I was ∼17 MeV nucleon −1 and outburst III required ∼0.3 MeV nucleon −1 . These cooling observations could not be explained without shallow heating. The shallow heating for outburst II was not well constrained and could vary from ∼0 to 2.2 MeV nucleon −1 , i.e., this outburst could in principle be explained without invoking shallow heating. We discuss the nature of the shallow heating and why it may occur at different strengths and depths during different outbursts.

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Section: Introductionmentioning

confidence: 99%

Different Accretion Heating of the Neutron Star Crust during Multiple Outbursts in MAXI J0556–332

Parikh

Homan

Wijnands

et al. 2017

ApJL

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“…For surface temperatures above ∼ 10 6 K and hydrogen columns larger than ∼10 5 g cm −2 , the energy deposited by nuclear burning becomes comparable to and larger than the interior luminosity (see left panel in Figure 3). The hydrogen column densities and surface temperatures where the DNB luminosity becomes non-negligible are in the range inferred from observations of neutron stars in LMXBs after accretion outbursts (see Wijnands et al 2017 for an observational overview). In Figure 4 we show the magnitude of the nuclear burning luminosity for varying hydrogen column (for T s = 1.26 × 10 6 K and T s = 3.16 × 10 6 K) in the top panel, and varying surface temperature in the bottom panel (for y H = 3.16 × 10 4 g cm −2 and y H = 3.16 × 10 6 g cm −2 ).…”

Section: Dnb Luminositymentioning

confidence: 77%

The effect of diffusive nuclear burning in neutron star envelopes on cooling in accreting systems

Wijngaarden

Chang

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Valuable information about the neutron star interior can be obtained by comparing observations of thermal radiation from a cooling neutron star crust with theoretical models. Nuclear burning of lighter elements that diffuse to deeper layers of the envelope can alter the relation between surface and interior temperatures and can change the chemical composition over time. We calculate new temperature relations and consider two effects of diffusive nuclear burning (DNB) for H-C envelopes. First, we consider the effect of a changing envelope composition and find that hydrogen is consumed on short timescales and our temperature evolution simulations correspond to those of a hydrogen-poor envelope within ∼100 days. The transition from a hydrogen-rich to a hydrogen-poor envelope is potentially observable in accreting NS systems as an additional initial decline in surface temperature at early times after the outburst. Second, we find that DNB can produce a non-negligible heat flux, such that the total luminosity can be dominated by DNB in the envelope rather than heat from the deep interior. However, without continual accretion, heating by DNB in H-C envelopes is only relevant for <1-80 days after the end of an accretion outburst, as the amount of light elements is rapidly depleted. Comparison to crust cooling data shows that DNB does not remove the need for an additional shallow heating source. We conclude that solving the time-dependent equations of the burning region in the envelope selfconsistently in thermal evolution models instead of using static temperature relations would be valuable in future cooling studies.

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“…Sources that intermittently show accretion-powered pulsations provide an independent measure on the difference between the TBO frequency and the spin frequency. These sources show a spin 1 Hz higher than the TBO frequency observed during an X-ray burst (see Casella et al 2008 for detail on Aql X-1, and for HETE J1900.1-2455 see Watts et al 2009). These observations provide a tight constraint on the rotating frame frequency of a buoyant r-mode, which must be as low as 1 Hz.…”

Section: Comparison With Observed Tbo Frequencies and Driftsmentioning

confidence: 92%

“…Since the work of PB05, a wealth of new models of thermonuclear X-ray bursts have been developed and fitted to bursts from specific sources; these models include a full treatment of the nuclear reactions in the ocean (Heger et al 2007;Keek & Heger 2017;Meisel 2018;Johnston et al 2018Johnston et al , 2019. A new heat source, shallow heating, has been suggested to resolve inconsistencies between observations and the theory needed to explain crust cooling models (for a review see ) and has implications for other phenomena such as short waiting time bursts, superburst recurrence times, and the transition between different burst regimes (Gupta et al 2007;Keek & Heger 2011, 2017. Including these effects can have a marked affect on frequency drift; Chambers et al (2019) calculated buoyant r-modes in a bursting ocean model developed by Keek & Heger (2017) that included both a changing composition and enhanced heat flux from the crust.…”

Section: Introductionmentioning

confidence: 99%

Relativistic ocean r-modes during type-I X-ray bursts

Chambers

Watts

2019

Monthly Notices of the Royal Astronomical Society

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Accreting neutron stars (NS) can exhibit high frequency modulations in their lightcurves during thermonuclear X-ray bursts, known as burst oscillations. These frequencies can be offset from the NS spin frequency by several Hz (where known independently) and can drift by 1 − 3 Hz. One plausible explanation is that a wave is present in the bursting ocean, the rotating frame frequency of which is the offset. The frequency of the wave should decrease (in the rotating frame) as the burst cools hence explaining the drift. A strong candidate is a buoyant r-mode. To date, models that calculated the frequency of this mode taking into account the radial structure neglected relativistic effects and predicted rotating frame frequencies of ∼ 4 Hz and frequency drifts of > 5 Hz; too large to be consistent with observations. We present a calculation that includes frame-dragging and gravitational redshift that reduces the rotating frame frequency by up to 30% and frequency drift by up to 20%. Updating previous models for the ocean cooling in the aftermath of the burst to a model more representative of detailed calculations of thermonuclear X-ray bursts reduces the frequency of the mode still further. This model, combined with relativistic effects, can reduce the rotating frequency of the mode to ∼ 2 Hz and frequency drift to ∼ 2 Hz, which is closer to the observed values.

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Cooling of Accretion-Heated Neutron Stars

Cited by 115 publications

References 193 publications

Different Accretion Heating of the Neutron Star Crust during Multiple Outbursts in MAXI J0556–332

Different Accretion Heating of the Neutron Star Crust during Multiple Outbursts in MAXI J0556–332

The effect of diffusive nuclear burning in neutron star envelopes on cooling in accreting systems

Relativistic ocean r-modes during type-I X-ray bursts

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