Type I X-ray bursts’ spectra and fuel composition from the atoll and transient source 4U 1730–22

Lu, Yongqi; Li, Zhaosheng; Pan, Y. Y.; Yu, Wenhui; Chen, Yupeng; Ji, Long; Ge, M. Y.; Zhang, Shu; Qu, J. L.; Song, Liming; Falanga, M.

doi:10.1051/0004-6361/202244984

Cited by 5 publications

(7 citation statements)

References 42 publications

(56 reference statements)

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“…The relativistic reflection model, relxillNS (Ludlam et al 2019;Connors et al 2020) 2 , describes the radiation reprocessed from an accretion disk around the NS, in which the seed photons are characterized by a blackbody spectrum. The assumptions of this model are consistent with the accretion disk illuminated by the burst radiation, which has been successfully explained by the deviations of the burst spectra in 4U 1636-536 and 4U 1730-22 (Zhao et al 2022;Lu et al 2023). In previous works the reflection model and the f a model improved the burst spectral fitting equally well; however, the burst temperatures and bolometric fluxes from the disk reflection model were less than the values from the f a model by the factors of ∼0.25 and 2.3, respectively.…”

Section: The Disk Reflection Modelsupporting

confidence: 54%

“…flux to the Eddington flux. In this work, for the first attempt, which is the same method proposed in Zhao et al (2022) and Lu et al (2023), we fitted the burst spectra by using the model TBabs × (bbodyrad + relxillNS). The persistent emission was regarded as background and was subtracted.…”

Section: The Disk Reflection Modelmentioning

confidence: 99%

“…Subsequently, the excesses are fitted well by using the double-blackbody model and the disk reflection model, which were adopted previously to fit the X-ray burst spectra from 4U 1820-30 (Keek et al 2018), SAX J1808.4-3658 (Bult et al 2021), and 4U 1636-536 and 4U 1730-22 (Zhao et al 2022Lu et al 2023). The double-blackbody and reflection models give a roughly equivalent interpretation that the soft excess tracks an interaction between the burst emission and the neutron star environment.…”

Section: Burst Spectral Fittingmentioning

confidence: 99%

“…The enhanced persistent emission during the X-ray bursts caused by the Poynting-Robertson drag has been proposed to produce the soft and hard excess in the burst Zand et al 2013;Worpel et al 2013;Güver et al 2021). Alternatively, the excess can also be explained by the burst emission that was reflected by the accretion disk (Zhao et al 2022;Lu et al 2023;Speicher et al 2022). 4U 1820-30 is a persistent and atoll X-ray source that was first discovered by the Uhuru satellite (Giacconi et al 1974).…”

Section: Introductionmentioning

confidence: 99%

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NICER views moderate, strong, and extreme photospheric expansion bursts from the ultracompact X-ray binary 4U 1820–30

Yu,

Li,

et al. 2024

A&A

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Type I X-ray bursts in the ultracompact X-ray binary 4U 1820--30 are powered by the unstable thermonuclear burning of hydrogen-deficient material. We report the detection of 15 type I X-ray bursts from 4U 1820--30 observed by between 2017 and 2023. All these bursts occurred in the low state for the persistent flux in the range of $2.5-8 erg cm^ $ in 0.1--250 keV. The burst spectra during the tail can be nicely explained by blackbody model. However, for the first sim 5 s after the burst onset, the time-resolved spectra showed strong deviations from the blackbody model. The significant improvement of the fit can be obtained by taking into account of the enhanced persistent emission due to the Poynting-Robterson drag, the extra emission modeled by another blackbody component, or by the reflection from the surrounding accretion disk. The reflection model provides a self-consistent and physically motivated explanation. We find that the accretion disk density changed with 0.5 s delay in response to the burst radiation, which indicates the distortion of the accretion disk during X-ray bursts. From the time-resolved spectroscopy, all bursts showed the characteristic of photospheric radius expansion (PRE). We find one superexpansion burst with the extreme photospheric radius $r_ ph >10^3$ km and blackbody temperature of $ 0.2$ keV, 13 strong PRE bursts for ph >10^2$ km, and one moderate PRE burst for $r_ ph km.

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Section: The Disk Reflection Modelsupporting

confidence: 54%

Section: The Disk Reflection Modelmentioning

confidence: 99%

Section: Burst Spectral Fittingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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NICER views moderate, strong, and extreme photospheric expansion bursts from the ultracompact X-ray binary 4U 1820–30

Yu,

Li,

et al. 2024

A&A

Self Cite

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“…Since their physics is relatively known, they are used as direct probes to study the accretion process by investigating the interactions between burst photons and materials surrounding the neutron star (Degenaar et al 2018). In observations, several processes have been studied through the changes of the persistent (nonburst) emission during bursts, including a hard X-ray shortage, an enhancement or a dip of the persistent emission, and an additional reflection component (e.g., Maccarone & Coppi 2003;Ballantyne 2004;Chen et al 2012;Worpel et al 2013;Ji et al 2014;Worpel et al 2015;Keek et al 2017Keek et al , 2018Fragile et al 2020;Bult et al 2021;Zhao et al 2022;Lu et al 2023;Speicher et al 2023). We note that previous studies were mainly based on bursts in normal LMXBs because of their large number, while the situation in AMXPs might be different.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Thermonuclear Bursts on Polar Caps of the Accreting X-Ray Millisecond Pulsar MAXI J1816-195

Ji,

Ge,

Chen

et al. 2024

ApJL

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We report accretion-powered pulsations for the first time during thermonuclear bursts in hard X-rays, which were observed with Insight-HXMT in 2022 during the outburst of the accreting X-ray millisecond pulsar MAXI J1816-195. By stacking 73 bursts, we detected pulse profiles in 8–30 and 30–100 keV during bursts, which are identical to those obtained from the persistent (nonburst) emission. On average, no significant phase lag was observed between burst and persistent pulse profiles. In addition, we suggest that the interaction with burst photons can be used as a direct diagnostic to distinguish contributions from the hot plasma near polar caps and the corona around the accretion disk, which are highly degenerate in their spectral shapes.

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New insight into the hard X-ray emission influenced by the type I bursts observed by Insight-HXMT during the outburst of 4U 1636–536

Peng,

Zhang,

Chen

et al. 2024

A&A

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Thermonuclear bursts, also known as type I X-ray bursts, result from unstable nuclear burning of H/He accreted to the surface of neutron stars, lasting from tens to hundreds of seconds. Thermonuclear bursts have an important impact on accretion environments around the neutron stars, such as their disks and coronas, and are therefore a subject of extensive research. Thermonuclear bursts can be used as probes to gain a deeper understanding of the properties of their disks and coronas. By analyzing the data from Insight-HXMT and NICER, we can determine the evolution of the significance of the hard shortage in 4U 1636--536 with its spectral state, as well as the evolution of the fraction of deficit with energy. Additionally, we investigate the possible geometry and evolution of the corona in 4U 1636--536 by combining our findings with the results of spectral analysis. We extracted the light curves from the Insight-HXMT low-energy, medium-energy, and high-energy data and subtracted their pre-burst emission, which allowed us to estimate the significance of the hard shortages during the bursts. By fitting the spectra, the correlation between the persistent spectral parameters and the significance of the hard shortages could be established. The bursts were then grouped according to the spectral state in which they occurred, and the significance of the hard shortages was estimated. These in turn helped to investigate the evolution of the fraction of deficit with energy. We find that during the soft state the significance of possible hard X-ray shortage in bursts is almost zero. However, in the hard state, some bursts exhibit significant shortages (>3 sigma ), while others do not. We attempt to establish a correlation between the significance of the hard X-ray shortage and the spectral parameters, but the data quality and the limited number of bursts prevent us from finding a strong correlation. For bursts with insignificant shortages in the soft state, the fraction of the deficit remains small. However, in the hard state the fraction of deficit for all bursts increases with energy, regardless of the significance of the shortage of individual bursts. For bursts during the hard state, we investigated the evolution of the fraction of deficit during the bursts by stacking the peaks and decays of the bursts, and find that as the flux of the bursts decreases, the energy corresponding to the maximum of the fraction of deficit becomes progressively higher. We explore the possible geometry and evolution of the corona suggested by the evolution of the fraction of deficit, which is obtained from the spectral and temporal analysis.

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Type I X-ray bursts’ spectra and fuel composition from the atoll and transient source 4U 1730–22

Cited by 5 publications

References 42 publications

NICER views moderate, strong, and extreme photospheric expansion bursts from the ultracompact X-ray binary 4U 1820–30

NICER views moderate, strong, and extreme photospheric expansion bursts from the ultracompact X-ray binary 4U 1820–30

The Influence of Thermonuclear Bursts on Polar Caps of the Accreting X-Ray Millisecond Pulsar MAXI J1816-195

New insight into the hard X-ray emission influenced by the type I bursts observed by Insight-HXMT during the outburst of 4U 1636–536

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