Reflecting on accretion in neutron star low-mass X-ray binaries

Ludlam, Renee M.

doi:10.1007/s10509-024-04281-y

Cited by 7 publications

(2 citation statements)

References 127 publications

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“…We also see that in both RELXILL and RELXILLNS, the emissivity index q is unphysically high, approaching the upper bound of 10 for RELXILLNS. We attempt to freeze these values at q = 3, a more reasonable value for NSs (Wilkins 2018;Ludlam 2024), but this only serves to worsen the χ 2 further. While this should not be taken as direct support that SLX 1735−269 is in fact a UCXB, this demonstrates that models with higher carbon and oxygen abundances do in fact provide a better explanation for the properties of the X-ray spectrum.…”

Section: Discussionmentioning

confidence: 99%

“…For NS LMXBs, this can provide an upper bound on the radius of the NS, which is important for understanding the NS equation of state (Cackett et al 2008;Miller et al 2013;Ludlam et al 2017). For a recent comprehensive review of reflection studies in NS LMXBs, see Ludlam (2024). In reflection studies we are therefore able to model the spectral contribution from 3-4 different components: nonthermal photons from the corona, thermal photons from the disk, reflected emission, and/or thermal emission from the NS and boundary layer itself.…”

Section: Introductionmentioning

confidence: 99%

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Investigating the Ultracompact X-Ray Binary Candidate SLX 1735-269 with NICER and NuSTAR

Moutard,

Ludlam,

Sudha

et al. 2024

ApJ

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We present two simultaneous NICER and NuSTAR observations of the ultracompact X-ray binary (UCXB) candidate SLX 1735−269 while the source was in two different spectral states. Using various reflection modeling techniques, we find that xillverCO, a model used for fitting X-ray spectra of UCXBs with high carbon and oxygen abundances is an improvement over relxill or relxillNS, which instead contains solar-like chemical abundances. This provides indirect evidence in support of the source being ultracompact. We also use this reflection model to get a preliminary measurement of the inclination of the system, i = 57 − 7 + 23 degrees. This is consistent with our timing analysis, where a lack of eclipses indicates an inclination of i < 80°. The timing analysis is otherwise inconclusive, and we cannot confidently measure the orbital period of the system.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigating the Ultracompact X-Ray Binary Candidate SLX 1735-269 with NICER and NuSTAR

Moutard,

Ludlam,

Sudha

et al. 2024

ApJ

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Broadband X-ray spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during the 2023 outburst

Li,

Kuiper,

Pan

et al. 2024

A&A

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We report on the broadband spectral and timing properties of the accreting millisecond X-ray pulsar during its April 2023 outburst. We used data from (1--10 keV) nustar \ (3--79 keV) (2--150 keV), and (30--150 keV). We detected significant 401 Hz pulsations across the 0.5--150 keV band. The pulse fraction increases from sim 2<!PCT!> at 1 keV to sim 13<!PCT!> at 66 keV. We detected five type-I X-ray bursts, including three photospheric radius expansion bursts, with a rise time of sim 2 s and an exponential decay time of sim 5 s. The recurrence time is sim 9.1 h, which can be explained by unstable thermonuclear burning of hydrogen-deficient material on the neutron star surface. The quasi-simultaneous 1--150 keV broadband spectra from nustar \ and can be aptly fitted by an absorbed reflection model relxillCp and a Gaussian line of instrumental origin. The Comptonized emission from the hot corona is characterized by a photon index Gamma of sim 1.8 and an electron temperature $kT_ e $ of sim 40 keV. We obtained a low inclination angle $i The accretion disk shows properties of strong ionization, $ erg cm over-solar abundance Fe 7.7$, and high density, $ e 19.5$. However, a lower disk density with normal abundance and ionization could also be possible. Based on the inner disk radius of in =1.67R_ ISCO $ and the long-term spin-down rate of $-3.1(2) Hz $, we were able to constrain the magnetic field of to the range of $(0.9-2.4) G.

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X-ray spectropolarimetric characterization of GX 340+0 in the horizontal branch: A highly inclined source?

La Monaca,

Di Marco,

Ludlam

et al. 2024

A&A

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We report the first detection of X-ray polarization in the horizontal branch for as obtained by the Imaging X-ray Polarimetry Explorer ( A polarization degree of 4.3<!PCT!>pm 0.4<!PCT!> at a confidence level of 68<!PCT!> is obtained. This value agrees with the previous polarization measurements of Z-sources in the horizontal branch. The spectropolarimetric analysis, performed using a broadband spectral model obtained by and quasi-simultaneous observations, allowed us to constrain the polarization for the soft and hard spectral components that are typical of these sources. The polarization angle for the two components differs by sim This result can be explained by a misalignment of the NS rotation axis with respect to the accretion disk axis. We compared the results with the polarization that is expected in different models. Theoretical expectations for the polarization of the disk and the Comptonization components favor a higher orbital inclination for than 60 as expected for Cyg-like sources. This is in contrast with the results we report for the reflection component based on the broadband spectrum.

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Reflecting on accretion in neutron star low-mass X-ray binaries

Cited by 7 publications

References 127 publications

Investigating the Ultracompact X-Ray Binary Candidate SLX 1735-269 with NICER and NuSTAR

Investigating the Ultracompact X-Ray Binary Candidate SLX 1735-269 with NICER and NuSTAR

Broadband X-ray spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during the 2023 outburst

X-ray spectropolarimetric characterization of GX 340+0 in the horizontal branch: A highly inclined source?

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