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Consistent accretion-induced heating of the neutron-star crust in MXB 1659-29 during two different outbursts

Consistent accretion-induced heating of the neutron-star crust in MXB 1659-29 during two different outbursts
Consistent accretion-induced heating of the neutron-star crust in MXB 1659-29 during two different outbursts

Monitoring the cooling of neutron-star crusts heated during accretion outbursts allows us to infer the physics of the dense matter present in the crust. We examine the crust cooling evolution of the low-mass X-ray binary MXB 1659-29 up to ∼505 days after the end of its 2015 outburst (hereafter outburst II) and compare it with what we observed after its previous 1999 outburst (hereafter outburst I) using data obtained from the Swift, XMM-Newton, and Chandra observatories. The observed effective surface temperature of the neutron star in MXB 1659ae -ae 29 dropped from ∼92 eV to ∼56 eV from ∼12 days to ∼505 days after the end of outburst II. The most recently performed observation after outburst II suggests that the crust is close to returning to thermal equilibrium with the core. We model the crust heating and cooling for both its outbursts collectively to understand the effect of parameters that may change for every outburst (e.g. the average accretion rate, the length of outburst, the envelope composition of the neutron star at the end of the outburst) and those which can be assumed to be the same during these two outbursts (e.g. the neutron star mass, its radius). Our modelling indicates that all parameters were consistent between the two outbursts with no need for any significant changes. In particular, the strength and the depth of the shallow heating mechanism at work (in the crust) were inferred to be consistent during both outbursts, contrary to what has been found when modelling the cooling curves after multiple outburst of another source, MAXI J0556-332. This difference in source behaviour is not understood. We discuss our results in the context of our current understanding of cooling of accretion-heated neutron-star crusts, and in particular with respect to the unexplained shallow heating mechanism.

Accretion, Accretion disks, Stars: neutron, X-rays: binaries, X-rays: individuals: MXB 1659-29
0004-6361
Parikh, A. S.
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Wijnands, R.
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Ootes, L. S.
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Page, D.
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Degenaar, N.
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Bahramian, A.
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Brown, E. F.
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Cackett, E. M.
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Cumming, A.
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Heinke, C.
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Homan, J.
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Rouco Escorial, A.
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Wijngaarden, M. J.P.
e6064827-8f6f-4fc4-b24d-140d11939237
Parikh, A. S.
21ab1c15-6144-40a1-ac71-618e02bc37d6
Wijnands, R.
382893ee-0e03-45e3-9321-db8b9fc74914
Ootes, L. S.
ad187f1b-e024-4fa3-8f53-afac44c52b8f
Page, D.
b47b77ff-942c-478f-9002-6d0b588e769b
Degenaar, N.
54149051-d74e-4e43-a7cd-501ec4023511
Bahramian, A.
1f016b89-98b9-4fa9-8df0-9390fbb5eeda
Brown, E. F.
357f29dd-cc4e-4a6e-9fea-4aad75253aa4
Cackett, E. M.
d14dd97a-9acb-4cf2-b9a7-17f9791fdee0
Cumming, A.
533b7dad-e34c-492f-a284-5b69a9c362be
Heinke, C.
f46b0379-2882-4b02-a633-476ad9f148ad
Homan, J.
549baf32-2442-4247-824e-21bb018b05f5
Rouco Escorial, A.
2277c2c1-0ae9-4f36-995b-0844702a11e9
Wijngaarden, M. J.P.
e6064827-8f6f-4fc4-b24d-140d11939237

Parikh, A. S., Wijnands, R., Ootes, L. S., Page, D., Degenaar, N., Bahramian, A., Brown, E. F., Cackett, E. M., Cumming, A., Heinke, C., Homan, J., Rouco Escorial, A. and Wijngaarden, M. J.P. (2019) Consistent accretion-induced heating of the neutron-star crust in MXB 1659-29 during two different outbursts. Astronomy and Astrophysics, 624, [A84]. (doi:10.1051/0004-6361/201834412).

Record type: Article

Abstract

Monitoring the cooling of neutron-star crusts heated during accretion outbursts allows us to infer the physics of the dense matter present in the crust. We examine the crust cooling evolution of the low-mass X-ray binary MXB 1659-29 up to ∼505 days after the end of its 2015 outburst (hereafter outburst II) and compare it with what we observed after its previous 1999 outburst (hereafter outburst I) using data obtained from the Swift, XMM-Newton, and Chandra observatories. The observed effective surface temperature of the neutron star in MXB 1659ae -ae 29 dropped from ∼92 eV to ∼56 eV from ∼12 days to ∼505 days after the end of outburst II. The most recently performed observation after outburst II suggests that the crust is close to returning to thermal equilibrium with the core. We model the crust heating and cooling for both its outbursts collectively to understand the effect of parameters that may change for every outburst (e.g. the average accretion rate, the length of outburst, the envelope composition of the neutron star at the end of the outburst) and those which can be assumed to be the same during these two outbursts (e.g. the neutron star mass, its radius). Our modelling indicates that all parameters were consistent between the two outbursts with no need for any significant changes. In particular, the strength and the depth of the shallow heating mechanism at work (in the crust) were inferred to be consistent during both outbursts, contrary to what has been found when modelling the cooling curves after multiple outburst of another source, MAXI J0556-332. This difference in source behaviour is not understood. We discuss our results in the context of our current understanding of cooling of accretion-heated neutron-star crusts, and in particular with respect to the unexplained shallow heating mechanism.

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Accepted/In Press date: 4 March 2019
e-pub ahead of print date: 15 April 2019
Published date: April 2019
Keywords: Accretion, Accretion disks, Stars: neutron, X-rays: binaries, X-rays: individuals: MXB 1659-29

Identifiers

Local EPrints ID: 431775
URI: http://eprints.soton.ac.uk/id/eprint/431775
ISSN: 0004-6361
PURE UUID: 4ebc1e81-1582-4f99-b854-2bbedc9ce2dc

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Date deposited: 14 Jun 2019 16:30
Last modified: 17 Mar 2024 12:26

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Contributors

Author: A. S. Parikh
Author: R. Wijnands
Author: L. S. Ootes
Author: D. Page
Author: N. Degenaar
Author: A. Bahramian
Author: E. F. Brown
Author: E. M. Cackett
Author: A. Cumming
Author: C. Heinke
Author: J. Homan
Author: A. Rouco Escorial
Author: M. J.P. Wijngaarden

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