The quiescent state of the neutron-star X-ray transient GRS 1747−312 in the globular cluster Terzan 6

Vats, Smriti; Wijnands, Rudy; Parikh, A. S.; Ootes, L. S.; Degenaar, N.; Page, Dany

doi:10.1093/mnras/sty733

Cited by 13 publications

(9 citation statements)

References 68 publications

(98 reference statements)

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“…Finally, an XMM observation of Terzan 6 taken when GRS 1747-312 was not in outburst showed evidence for a single X-ray source with L X ∼ 10 33 erg s −1 (assuming our distance of 6.8 kpc). A spectral fit to this source required a two-component model with both a neutron star atmosphere and a hard power law, consistent with ongoing low-level accretion onto a neutron star (Vats et al 2018). This X-ray luminosity is well below that of our Swift/XRT observations, which range from L X ∼ 7 × 10 33 to 4 × 10 34 erg s −1 .…”

Section: U 1746-37 In Ngc 6441supporting

confidence: 51%

“…Therefore we have taken the approach of fitting two models to each of the Swift/XRT observations: one with fixed Γ and free N H , and the other with both Γ and N H fixed, the latter to the estimated foreground of 1.4 × 10 22 cm −2 . Motivated by the typical photon indices for low-mass X-ray binaries at these X-ray luminosities and the spectral fitting results of (Vats et al 2018) for the source in quiescence, for the models with Γ fixed, we assume Γ = 1.7.…”

Section: U 1746-37 In Ngc 6441mentioning

confidence: 99%

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The MAVERIC Survey: Variable Jet-Accretion Coupling in Luminous Accreting Neutron Stars in Galactic Globular Clusters

Panurach,

Strader,

Bahramian

et al. 2021

Preprint

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Accreting neutron stars in low-mass X-ray binaries show outflows-and sometimes jets-in the general manner of accreting black holes. However, the quantitative link between the accretion flow (traced by X-rays) and outflows and/or jets (traced by radio emission) is much less well-understood for neutron stars than for black holes, other than the general observation that neutron stars are fainter in the radio at a given X-ray luminosity. We use data from the deep MAVERIC radio continuum survey of Galactic globular clusters for a systematic radio and X-ray study of six luminous (L X > 10 34 erg s −1 ) persistent neutron star X-ray binaries in our survey, as well as two other transient systems also captured by our data. We find that these neutron star X-ray binaries show an even larger range in radio luminosity than previously observed. In particular, in quiescence at L X ∼ 3 × 10 34 erg s −1 , the confirmed neutron star binary GRS 1747-312 in Terzan 6 sits near the upper envelope of the black hole radio/X-ray correlation, and the persistently accreting neutron star systems AC 211 (in M15) and X1850-087 (in NGC 6712) show unusual radio variability and luminous radio emission. We interpret AC 211 as an obscured "Z source" that is accreting at close to the Eddington limit, while the properties of X1850-087 are difficult to explain, and motivate future coordinated radio and X-ray observations. Overall, our results show that neutron stars do not follow a single relation between inflow and outflow, and confirm that their accretion dynamics are more complex than for black holes.

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Section: U 1746-37 In Ngc 6441supporting

confidence: 51%

Section: U 1746-37 In Ngc 6441mentioning

confidence: 99%

The MAVERIC Survey: Variable Jet-Accretion Coupling in Luminous Accreting Neutron Stars in Galactic Globular Clusters

Panurach,

Strader,

Bahramian

et al. 2021

Preprint

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“…The X-ray spectrum in the range of 0.5 − 10 keV for lowlevel accreting NSs can generally be well fitted with the model with two components, i.e., a thermal soft X-ray component plus a power-law component (e.g. Jonker et al 2004b;Campana et al 2008a,b;Fridriksson et al 2010Fridriksson et al , 2011Armas Padilla et al 2013a;Degenaar et al 2013;Campana et al 2014;Parikh et al 2017;Vats et al 2018). For certain low-level accreting NSs, the temperature of the soft X-ray component decreases with decreasing the X-ray luminosity during the decay after the outburst (Armas Padilla et al 2013b;Degenaar et al 2013;Bahramian et al 2014).…”

Section: Introductionmentioning

confidence: 88%

A systematic study of the advection-dominated accretion flow for the origin of the X-ray emission in weakly magnetized low-level accreting neutron stars

Qiao

Liu

2019

Monthly Notices of the Royal Astronomical Society

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Observationally, the X-ray spectrum (0.5 − 10 keV) of low-level accreting neutron stars (NSs) (L 0.5−10keV 10 36 erg s −1 ) can generally be well fitted by the model with two components, i.e, a thermal soft X-ray component plus a power-law component. Meanwhile, the fractional contribution of the power-law luminosity η (η ≡ L power law 0.5−10keV /L 0.5−10keV ) varies with the X-ray luminosity L 0.5−10keV . In this paper, we systematically investigate the origin of such X-ray emission within the framework of the advection-dominated accretion flow (ADAF) around a weakly magnetized NS, in which the thermal soft X-ray component arises from the surface of the NS and the power-law component arises from the ADAF itself. We test the effects of the viscosity parameter α in the ADAF and thermalized parameter f th (describing the fraction of the ADAF energy released at the surface of the NS as thermal emission) on the relation of η versus L 0.5−10keV . It is found that η is nearly a constant (∼ zero) with L 0.5−10keV for different α with f th = 1, which is inconsistent with observations. Meanwhile, it is found that a change of f th can significantly change the relation of η versus L 0.5−10keV . By comparing with a sample of non-pulsating NS-low mass X-ray binaries probably dominated by low-level accretion onto NSs, it is found that a small value of f th 0.1 is needed to match the observed range of η 10% in the diagram of η versus L 0.5−10keV . Finally, we argue that the small value of f th 0.1 implies that the radiative efficiency of NSs with an ADAF accretion may not be as high as the predicted result previously of ǫ ∼Ṁ GM R * /Ṁc 2 ∼ 0.2 despite the existence of the hard surface.

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“…It is possible that there are multiple transient LMXBs residing in Terzan 6 which are not resolved by Swift/XRT (given its high encounter rate, Bahramian et al 2013). An outburst detected by Suzaku did not show an eclipse at the predicted time, which might indicate a second LMXB in the cluster (Saji et al 2016), though Vats et al (2018) argue that it could be the same LMXB. We confirmed the outburst detected in our survey was from GRS 1747−312 by performing a follow-up Swift/XRT observation at the time of one predicted eclipse ingress (in 't Zand et al 2003), which successfully detected the eclipse.…”

Section: Known X-ray Binariesmentioning

confidence: 88%

The Swift Bulge Survey: Motivation, Strategy, and First X-ray Results

Bahramian,

Heinke,

Kennea

et al. 2020

Preprint

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Very faint X-ray transients (VFXTs) are X-ray transients with peak X-ray luminosities (L X ) of L X < ∼ 10 36 erg s −1 , which are not well-understood. We carried out a survey of 16 square degrees of the Galactic Bulge with the Swift Observatory, using short (60 s) exposures, and returning every 2 weeks for 19 epochs in 2017-18 (with a gap from November 2017 to February 2018, when the Bulge was in sun-constraint). Our main goal was to detect and study VFXT behaviour in the Galactic Bulge across various classes of X-ray sources. In this work, we explain the observing strategy of the survey, compare our results with the expected number of source detections per class, and discuss the constraints from our survey on the Galactic VFXT population. We detected 91 X-ray sources, of which 45 have known counterparts: 17 chromospherically active stars, 12 X-ray binaries, 5 cataclysmic variables (and 4 candidates), 3 symbiotic systems, 2 radio pulsars, 1 AGN, and a young star cluster. The other 46 are of previously undetermined nature. We utilize X-ray hardness ratios, searches for optical/infrared counterparts in published catalogs, and flux ratios from quiescence to outburst to constrain the nature of the unknown sources. Of these 46, 7 are newly discovered hard transients, which are likely VFXT X-ray binaries. Furthermore, we find strong new evidence for a symbiotic nature of 4 sources in our full sample, and new evidence for accretion power in 6 X-ray sources with optical counterparts. Our findings indicate that a large subset of VXFTs is likely made up of symbiotic systems.

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The quiescent state of the neutron-star X-ray transient GRS 1747−312 in the globular cluster Terzan 6

Cited by 13 publications

References 68 publications

The MAVERIC Survey: Variable Jet-Accretion Coupling in Luminous Accreting Neutron Stars in Galactic Globular Clusters

The MAVERIC Survey: Variable Jet-Accretion Coupling in Luminous Accreting Neutron Stars in Galactic Globular Clusters

A systematic study of the advection-dominated accretion flow for the origin of the X-ray emission in weakly magnetized low-level accreting neutron stars

The Swift Bulge Survey: Motivation, Strategy, and First X-ray Results

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