The corona contracts in a black-hole transient

Kara, Erin; Steiner, James F.; Fabian, A. C.; Cackett, Edward M.; Uttley, P.; Remillard, Ron; Gendreau, Keith C.; Arzoumanian, Zaven; Altamirano, D.; Eikenberry, S. S.; Enoto, Teruaki; Homan, J.; Neilsen, Joey; Stevens, Abigail

doi:10.1038/s41586-018-0803-x

Cited by 258 publications

(363 citation statements)

References 33 publications

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“…There is also a clear narrow core to the iron emission. The broad component of the iron line appears remarkably stable throughout the outburst, while the relative strength of the narrow core reduces with time; this behaviour is also seen in observations by NICER (Kara et al 2019). Additionally, the relative high energy flux increases during the outburst, possibly indicating an increase in coronal temperature.…”

Section: Qualitative Comparisonsupporting

confidence: 63%

MAXI J1820+070 with NuSTAR I. An increase in variability frequency but a stable reflection spectrum: coronal properties and implications for the inner disc in black hole binaries

Buisson

Fabian

Barret

et al. 2019

Monthly Notices of the Royal Astronomical Society

103

185

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MAXI J1820+070 (optical counterpart ASASSN-18ey) is a black hole candidate discovered through its recent very bright outburst. The low extinction column and long duration at high flux allow detailed measurements of the accretion process to be made. In this work, we compare the evolution of X-ray spectral and timing properties through the initial hard state of the outburst. We show that the inner accretion disc, as measured by relativistic reflection, remains steady throughout this period of the outburst. Nevertheless, subtle spectral variability is observed, which is well explained by a change in coronal geometry. However, characteristic features of the temporal variability -lowfrequency roll-over and QPO frequency -increase drastically in frequency, as the outburst proceeds. This suggests that the variability timescales are governed by coronal conditions rather than solely by the inner disc radius. We also find a strong correlation between X-ray luminosity and coronal temperature. This can be explained by electron pair production with a changing effective radius and a non-thermal electron fraction of ∼ 20%.

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Section: Qualitative Comparisonsupporting

confidence: 63%

MAXI J1820+070 with NuSTAR I. An increase in variability frequency but a stable reflection spectrum: coronal properties and implications for the inner disc in black hole binaries

Buisson

Fabian

Barret

et al. 2019

Monthly Notices of the Royal Astronomical Society

103

185

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“…A broad line profile with a strong red wing was also observed in the 4-8 keV range in the super-Eddington regime. This is the first time that such a broad asymmetric Fe line has been detected in a stronglymagnetized accreting neutron star (see also Miller et al 2018 andKara et al 2019 for NICER spectral capabilities in the Fe-band). The 6.4 keV line is identified as a fluorescent line from neutral or weakly ionized Fe, whereas the 6.67 and 6.98 keV lines originate from highly ionized He-like and H-like Fe ions, respectively.…”

Section: Evolution Of Iron Linesmentioning

confidence: 71%

An Evolving Broad Iron Line from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124

Jaisawal

Wilson-Hodge

Fabian

et al. 2019

ApJ

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We present a spectral study of the ultraluminous Be/X-ray transient pulsar Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER) observations during the system's 2017-2018 giant outburst. The 1.2-10 keV energy spectrum of the source can be approximated with an absorbed cut-off power law model. We detect strong, luminosity-dependent emission lines in the 6-7 keV energy range. A narrow 6.42 keV line, observed in the sub-Eddington regime, is seen to evolve into a broad Fe-line profile in the super-Eddington regime. Other features are found at 6.67 and 6.97 keV in the Fe-line complex. An asymmetric broad line profile, peaking at 6.67 keV, is possibly due to Doppler effects and gravitational redshift. The 1.2-79 keV broadband spectrum from NuSTAR and NICER observations at the outburst peak is well described by an absorbed cut-off power law plus multiple Gaussian lines and a blackbody component. Physical reflection models are also tested to probe the broad iron line feature. Depending on the mass accretion rate, we found emission sites that are evolving from ∼5000 km to a range closer to the surface of the neutron star. Our findings are discussed in the framework of the accretion disk and its implication on the magnetic field, the presence of optically thick accretion curtain in the magnetosphere, jet emission, and the massive, ultra-fast outflow expected at super-Eddington accretion rates. We do not detect any signatures of a cyclotron absorption line in the NICER or NuSTAR data.

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“…This can be attributed to the 'compactification' of the corona. In this paradigm, the ratio of the scale-height of the corona (h) to R in decreases with decreasing spectral hardness (Kara et al 2019). Another possible scenario is when the radius of the co-rotating slab corona decreases, thereby leading to a softer emission (Zhang et al 2019).…”

Section: Reflection Strength (R S )mentioning

confidence: 99%

Evolution of the Accretion Disk–Corona during the Bright Hard-to-soft State Transition: A Reflection Spectroscopic Study with GX 339–4

Sridhar

García

Steiner

et al. 2020

ApJ

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We present the analysis of several observations of the black hole binary GX 339-4 during its bright intermediate states from two different outbursts (2002 and 2004), as observed by RXTE/PCA. We perform a consistent study of its reflection spectrum by employing the relxill family of relativistic reflection models to probe the evolutionary properties of the accretion disk including the inner disk radius (R in ), ionization parameter (ξ), temperatures of the inner disk (T in ), corona (kT e ), and its optical depth (τ ). Our analysis indicates that the disk inner edge approaches the inner-most stable circular orbit (ISCO) during the early onset of bright hard state, and that the truncation radius of the disk remains low (< 9R g ) throughout the transition from hard to soft state. This suggests that the changes observed in the accretion disk properties during the state transition are driven by variation in accretion rate, and not necessarily due to changes in the inner disk's radius. We compare the aforementioned disk properties in two different outbursts with state transitions occurring at dissimilar luminosities, and find identical evolutionary trends in the disk properties, with differences only seen in corona's kT e and τ . We also perform an analysis by employing a self-consistent Comptonized accretion disk model accounting for the scatter of disk photons by the corona, and measure low inner disk truncation radius across the bright intermediate states, using the temperature dependent values of spectral hardening factor, thereby independently confirming our results from the reflection spectrum analysis.

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The corona contracts in a black-hole transient

Cited by 258 publications

References 33 publications

MAXI J1820+070 with NuSTAR I. An increase in variability frequency but a stable reflection spectrum: coronal properties and implications for the inner disc in black hole binaries

MAXI J1820+070 with NuSTAR I. An increase in variability frequency but a stable reflection spectrum: coronal properties and implications for the inner disc in black hole binaries

An Evolving Broad Iron Line from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124

Evolution of the Accretion Disk–Corona during the Bright Hard-to-soft State Transition: A Reflection Spectroscopic Study with GX 339–4

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