Absence of Reflection Features in NuSTAR Spectra of the Luminous Neutron Star X-Ray Binary GX 5–1

Homan, J.; Steiner, James F.; Lin, Dacheng; Fridriksson, Joel K.; Remillard, Ron; Miller, J. M.; Ludlam, R. M.

doi:10.3847/1538-4357/aaa439

Cited by 21 publications

(22 citation statements)

References 47 publications

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“…In contrast to 4U 1746−371, GX 13+1 continuously shows a broad Fe line component and narrow Fe absorption features indicative of winds (Díaz Trigo et al 2012). This could be due to the fact that Fe line flux is cor-10 -3 10 -2 10 -1 10 0 F Edd Another source was recently found to not have reflection features present in its persistent spectrum: the Z source GX 5−1 (Homan et al 2018). The likeliest explanation for the absence of reflection features was a highly ionized disk given the sources high luminosity (L 1−100 keV = 2.97 × 10 38 − 4.27 × 10 38 ergs s −1 ).…”

Section: Discussionmentioning

confidence: 99%

NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371

Ludlam

Miller

Barret

et al. 2019

ApJ

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Atoll sources are accreting neutron star (NS) low-mass X-ray binaries. We present a spectral analysis of four persistent atoll sources (GX 3+1, 4U 1702−429, 4U 0614+091, and 4U 1746−371) observed for ∼ 20 ks each with NuSTAR to determine the extent of the inner accretion disk. These sources range from an apparent luminosity of 0.006 − 0.11 of the Eddington limit (assuming the empirical limit of 3.8 × 10 38 ergs s −1 ). Broad Fe emission features shaped by Doppler and relativistic effects close to the NS were firmly detected in three of these sources. The position of the disk appears to be close to the innermost stable circular orbit (ISCO) in each case. For GX 3+1, we determine R in = 1.8 +0.2 −0.6 R ISCO (90% confidence level) and an inclination of 27 • −31 • . For 4U 1702−429, we find a R in = 1.5 +1.6 −0.4 R ISCO and inclination of 53 • − 64 • . For 4U 0614+091, the disk has a position of R in = 1.3 +5.4 −0.2 R ISCO and inclination of 50 • −62 • . If the disk does not extend to the innermost stable circular orbit, we can place conservative limits on the magnetic field strength in these systems in the event that the disk is truncated at the Alfvén radius. This provides the limit at the poles of B ≤ 6.7 × 10 8 G, 3.3 × 10 8 G, and 14.5 × 10 8 G for GX 3+1, 4U 1702−429, and 4U 0614+091, respectively. For 4U 1746−371, we argue that the most plausible explanation for the lack of reflection features is a combination of source geometry and strong Comptonization. We place these sources among the larger sample of NSs that have been observed with NuSTAR.

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Section: Discussionmentioning

confidence: 99%

NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371

Ludlam

Miller

Barret

et al. 2019

ApJ

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“…In conclusion, our analysis shows that although we do not have clear evidence of a broad emission line in the Fe-K region, a relativistic smeared reflection component is necessary to fit the 0.3-40 keV broadband spectrum. The lack of residuals associated with a broad emission line is likely due to the available low statistics in the Fe-K region, unlike the source GX 5-1 for which the lack of the broad emission line is explained as being due to the high ionization parameter (see Homan et al 2018). Our prediction will be confirmed in the near future, after the launch of the enhanced X-Ray Timing and Polarimetry (eXTP; De Rosa et al 2019) observatory.…”

Section: Discussionmentioning

confidence: 53%

Reflection component in the Bright Atoll Source GX 9+9

Iaria

Mazzola

Salvo

et al. 2020

A&A

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Context. GX 9+9 (4U 1728-16) is a low mass X-ray binary (LMXB) source harboring a neutron star. Although it belongs to the subclass of the bright Atoll sources together with GX 9+1, GX 3+1, and GX 13+1, its broadband spectrum is poorly studied and apparently does not show reflection features in the spectrum. Aims. To constrain the continuum well and verify whether a relativistic smeared reflection component is present, we analyze the broadband spectrum of GX 9+9 using BeppoSAX and XMM-Newton spectra covering the 0.3-40 keV energy band. Methods. We fit the spectrum adopting a model composed of a disk-blackbody plus a Comptonized component whose seed photons have a blackbody spectrum (Eastern Model). A statistically equivalent model is composed of a Comptonized component whose seed photons have a disk-blackbody distribution plus a blackbody that mimics a saturated Comptonization likely associated with a boundary layer (Western model). Other trials did not return a good fit.Results. The spectrum of GX 9+9 was observed in a soft state and its luminosity is 2.3 × 10 37 erg s −1 assuming a distance to the source of 5 kpc. In the Eastern Model scenario, we find the seed-photon temperature and electron temperature of the Comptonized component to be 1.14 +0.10 −0.07 keV and 2.80 +0.09 −0.04 keV, respectively, while the optical depth of the Comptonizing corona is 8.9 ± 0.4. The color temperature of the inner accretion disk is 0.86 +0.08 −0.02 keV and 0.82 ± 0.02 keV for the BeppoSAX and XMM-Newton spectrum, respectively. In the Western Model scenario, instead, we find that the seed-photon temperature is 0.87 ± 0.07 keV and 1.01 ± 0.08 keV for the BeppoSAX and XMM-Newton spectrum, respectively. The electron temperature of the Comptonized component is 2.9 ± 0.2 keV, while the optical depth is 9.4 +1.5 −1.1 . The blackbody temperature is 1.79 +0.09 −0.18 keV and 1.85 +0.07 −0.15 keV for the BeppoSAX and XMM-Newton spectrum, respectively. The addition of a relativistic smeared reflection component improved the fit in both the scenarios, giving compatible values of the parameters, even though a significant broad emission line in the Fe-K region is not observed. Conclusions. From the reflection component we estimated an inclination angle of about 43 +6−4 deg and 51 +9 −2 deg for the Eastern and Western Model, respectively. The value of the reflection fraction Ω/2π is 0.18 ± 0.04 and 0.21 ± 0.03 for the Eastern and Western Model, respectively, suggesting that the Comptonized corona should be compact and close to the innermost region of the system.

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“…In the end, we tested also the model used by Homan et al (2018), composed of two thermal component, a power-law and a Gaussian component to fit the iron emission line at 6.6 keV, plus a TBabs component to take into account the absorption due to the interstellar medium. For the NB spectrum, we inferred a χ 2 /d.o.f.…”

Section: Modelmentioning

confidence: 99%

“…Hence, the whole reflection spectrum is believed to be modified by transverse Doppler shifts, Doppler broadening, relativistic Doppler boosting and gravitational redshift, which produce the characteristic broad and skewed line profile (Fabian et al 1989). On the other hand, there are some Z-sources where reflection spectral components are absent (as for example the source GX 5-1, see Bhulla et al 2019;Homan et al 2018;Jackson et al 2009), suggesting different geometries or accretion flow properties or different metallicities.…”

Section: Introductionmentioning

confidence: 99%

“…The authors showed that the hard tail was well described by a power-law shape without cut-off up to 200-300 keV, proposing that it originates as a Compton up-scattering of soft seed photons on electrons with a non-thermal distribution. Homan et al (2018) partially analysed the NuSTAR observation of Sco X-1 reported here, in order to compare the results with those obtained in their study of the Z-source GX 5-1. Here, we extended the analysis of NuSTAR data, studying the 3-60 keV spectra extracted for NB and FB with two different classes of models which lead to the same physical description of the source.…”

Section: Introductionmentioning

confidence: 99%

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Fe K$α$ and Fe K$β$ line detection in the NuSTAR spectrum of the ultra-bright Z-source Scorpius X-1

Mazzola,

Iaria,

Di Salvo

et al. 2021

Preprint

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Context. Low-mass X-ray binaries hosting a low-magnetised neutron star, which accretes matter via Roche-lobe overflow, are generally grouped in two classes, named Atoll and Z sources after the path described in their X-ray colour-colour diagrams. Scorpius X-1 is the brightest persistent low-mass X-ray binary known so far, and it is the prototype of the Z sources.Aims. We analysed the first NuSTAR observation of this source to study its spectral emission exploiting the high statistics data collected by this satellite. Examining the colour-colour diagram, the source was probably observed during the lower normal and flaring branches of its Z-track. We separated the data from the two branches in order to investigate the evolution of the source along the track. Methods. We fitted the 3-60 keV NuSTAR spectra using the same models for both the branches. We adopted two description for the continuum: in the first case we used a blackbody and a thermal Comptonisation with seed photons originating in the accretion disc; in the second one, we adopted a disc-blackbody and a Comptonisation with a blackbodyshaped spectrum of the incoming seed photons. A power-law fitting the high energy emission above 20 keV was also required in both cases.Results. The two models provide the same physical scenario for the source in both the branches: a blackbody temperature between 0.8 and 1.5 keV, a disc-blackbody with temperature between 0.4 and 0.6 keV, and an optically thick Comptonising corona with optical depth between 6 and 10 and temperature about 3 keV. Furthermore, two lines related to the Kα and Kβ transitions of the He-like Fe xxv ions were detected at 6.6 keV and 7.8 keV, respectively. A hard tail modelled by a power law with a photon index between 2 and 3 was also required for both the models.

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Absence of Reflection Features in NuSTAR Spectra of the Luminous Neutron Star X-Ray Binary GX 5–1

Cited by 21 publications

References 47 publications

NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371

NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371

Reflection component in the Bright Atoll Source GX 9+9

Fe K$α$ and Fe K$β$ line detection in the NuSTAR spectrum of the ultra-bright Z-source Scorpius X-1

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