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A NICER look at thermonuclear X-ray bursts from Aql X-1

A NICER look at thermonuclear X-ray bursts from Aql X-1
A NICER look at thermonuclear X-ray bursts from Aql X-1
We present spectral and temporal properties of all the thermonuclear X-ray bursts observed from Aql X-1 by the Neutron Star Interior and Composition Explorer (NICER) between 2017 July and 2021 April. This is the first systematic investigation of a large sample of type I X-ray bursts from Aql X-1 with improved sensitivity at low energies. We detect 22 X-ray bursts including two short recurrence burst events in which the separation was only 451 s and 496 s. We perform time resolved spectroscopy of the bursts using the fixed and scaled background (fa method) approaches. We show that the use of a scaling factor to the pre-burst emission is the statistically preferred model in about 68 per cent of all the spectra compared to the fixed background approach. Typically the fa values are clustered around 1–3, but can reach up to 11 in a burst where photospheric radius expansion is observed. Such fa values indicate a very significant increase in the pre-burst emission especially at around the peak flux moments of the bursts. We show that the use of the fa factor alters the best-fitting spectral parameters of the burst emission. Finally, we employed a reflection model instead of scaling the pre-burst emission. We show that reflection models also do fit the spectra and improve the goodness of the fits. In all cases, we see that the disc is highly ionized by the burst emission and the fraction of the reprocessed emission to the incident burst flux is typically clustered around 20 per cent.
0035-8711
1577–1596
Güver, Tolga
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Boztepe, Tuğba
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Ballantyne, D.R.
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Bostancı, Z. Funda
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Bult, Peter
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Jaisawal, Gaurava K.
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Göğüş, Ersin
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Strohmayer, Tod E.
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Altamirano, Diego
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Guillot, Sebastien
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Chakrabarty, Deepto
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Güver, Tolga
42c68e75-5602-4ddf-a230-07264c1308f4
Boztepe, Tuğba
cf8284ac-461e-4d1d-a0aa-49d5a9a1146b
Ballantyne, D.R.
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Bostancı, Z. Funda
8026d87a-e2f3-4eb8-9f29-b0f0db0e0a5c
Bult, Peter
8306a3c0-8aac-4761-b719-4d5d2b40d066
Jaisawal, Gaurava K.
4d5dcd39-0881-426d-8ad7-f378238405ae
Göğüş, Ersin
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Strohmayer, Tod E.
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Altamirano, Diego
d5ccdb09-0b71-4303-9538-05b467be075b
Guillot, Sebastien
307953c0-47da-4e92-8caf-5ae719f02c52
Chakrabarty, Deepto
2fbe9d21-20d7-4db8-a75c-92b0ed8b30a4

Güver, Tolga, Boztepe, Tuğba, Ballantyne, D.R., Bostancı, Z. Funda, Bult, Peter, Jaisawal, Gaurava K., Göğüş, Ersin, Strohmayer, Tod E., Altamirano, Diego, Guillot, Sebastien and Chakrabarty, Deepto (2021) A NICER look at thermonuclear X-ray bursts from Aql X-1. Monthly Notices of the Royal Astronomical Society, 510 (2), 1577–1596. (doi:10.1093/mnras/stab3422).

Record type: Article

Abstract

We present spectral and temporal properties of all the thermonuclear X-ray bursts observed from Aql X-1 by the Neutron Star Interior and Composition Explorer (NICER) between 2017 July and 2021 April. This is the first systematic investigation of a large sample of type I X-ray bursts from Aql X-1 with improved sensitivity at low energies. We detect 22 X-ray bursts including two short recurrence burst events in which the separation was only 451 s and 496 s. We perform time resolved spectroscopy of the bursts using the fixed and scaled background (fa method) approaches. We show that the use of a scaling factor to the pre-burst emission is the statistically preferred model in about 68 per cent of all the spectra compared to the fixed background approach. Typically the fa values are clustered around 1–3, but can reach up to 11 in a burst where photospheric radius expansion is observed. Such fa values indicate a very significant increase in the pre-burst emission especially at around the peak flux moments of the bursts. We show that the use of the fa factor alters the best-fitting spectral parameters of the burst emission. Finally, we employed a reflection model instead of scaling the pre-burst emission. We show that reflection models also do fit the spectra and improve the goodness of the fits. In all cases, we see that the disc is highly ionized by the burst emission and the fraction of the reprocessed emission to the incident burst flux is typically clustered around 20 per cent.

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2111.12105 - Accepted Manuscript
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Accepted/In Press date: 22 November 2021
Published date: 26 November 2021
Additional Information: arXiv:2111.12105

Identifiers

Local EPrints ID: 455536
URI: http://eprints.soton.ac.uk/id/eprint/455536
ISSN: 0035-8711
PURE UUID: c88e8274-cdda-40ee-8964-52622ef8d3d6
ORCID for Diego Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 24 Mar 2022 17:41
Last modified: 25 Mar 2022 02:42

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Contributors

Author: Tolga Güver
Author: Tuğba Boztepe
Author: D.R. Ballantyne
Author: Z. Funda Bostancı
Author: Peter Bult
Author: Gaurava K. Jaisawal
Author: Ersin Göğüş
Author: Tod E. Strohmayer
Author: Sebastien Guillot
Author: Deepto Chakrabarty

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