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

The effect of diffusive nuclear burning in neutron star envelopes on cooling in accreting systems
The effect of diffusive nuclear burning in neutron star envelopes on cooling in accreting systems
Valuable information about the neutron star (NS) interior can be obtained by comparing observations of thermal radiation from a cooling NS 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 time-scales and our temperature evolution simulations correspond to those of a hydrogen-poor envelope within ∼100 d. 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 d 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 self-consistently in thermal evolution models instead of using static temperature relations would be valuable in future cooling studies.
0035-8711
4936-4944
Wijngaarden, M. J. P.
e6064827-8f6f-4fc4-b24d-140d11939237
Ho, Wynn C.G.
d78d4c52-8f92-4846-876f-e04a8f803a45
Chang, Philip
7f213428-5533-49c7-bd52-a5a2feee4792
Page, Dany
5f9c4edb-50e2-4d9d-bf5d-284293446739
Wijnands, Rudy
4ac16ff6-b564-4e5d-89d4-36ff92c6030c
Ootes, Laura S.
0802e0df-5910-44f3-8fc3-e82aad94c34c
Cumming, Andrew
32f48ee9-7fac-4a2b-9b92-388acca15654
Degenaar, Nathalie
347a2379-6b78-482e-976c-52f08a96114d
Beznogov, Mikhail
50a96abd-1d56-4274-8d7f-ca6a0681b4d8
Wijngaarden, M. J. P.
e6064827-8f6f-4fc4-b24d-140d11939237
Ho, Wynn C.G.
d78d4c52-8f92-4846-876f-e04a8f803a45
Chang, Philip
7f213428-5533-49c7-bd52-a5a2feee4792
Page, Dany
5f9c4edb-50e2-4d9d-bf5d-284293446739
Wijnands, Rudy
4ac16ff6-b564-4e5d-89d4-36ff92c6030c
Ootes, Laura S.
0802e0df-5910-44f3-8fc3-e82aad94c34c
Cumming, Andrew
32f48ee9-7fac-4a2b-9b92-388acca15654
Degenaar, Nathalie
347a2379-6b78-482e-976c-52f08a96114d
Beznogov, Mikhail
50a96abd-1d56-4274-8d7f-ca6a0681b4d8

Wijngaarden, M. J. P., Ho, Wynn C.G., Chang, Philip, Page, Dany, Wijnands, Rudy, Ootes, Laura S., Cumming, Andrew, Degenaar, Nathalie and Beznogov, Mikhail (2020) The effect of diffusive nuclear burning in neutron star envelopes on cooling in accreting systems. Monthly Notices of the Royal Astronomical Society, 493 (4), 4936-4944. (doi:10.1093/mnras/staa595).

Record type: Article

Abstract

Valuable information about the neutron star (NS) interior can be obtained by comparing observations of thermal radiation from a cooling NS 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 time-scales and our temperature evolution simulations correspond to those of a hydrogen-poor envelope within ∼100 d. 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 d 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 self-consistently in thermal evolution models instead of using static temperature relations would be valuable in future cooling studies.

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2003.09307 - Accepted Manuscript
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Accepted/In Press date: 26 February 2020
Published date: 18 March 2020

Identifiers

Local EPrints ID: 439418
URI: http://eprints.soton.ac.uk/id/eprint/439418
ISSN: 0035-8711
PURE UUID: 263e6b8c-10d5-4848-95d5-82dbc7617466
ORCID for Wynn C.G. Ho: ORCID iD orcid.org/0000-0002-6089-6836

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Date deposited: 22 Apr 2020 16:30
Last modified: 26 Nov 2021 02:54

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Contributors

Author: Wynn C.G. Ho ORCID iD
Author: Philip Chang
Author: Dany Page
Author: Rudy Wijnands
Author: Laura S. Ootes
Author: Andrew Cumming
Author: Nathalie Degenaar
Author: Mikhail Beznogov

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