We present measurements of the dimensionless spin parameters and inner-disk inclination of two stellar mass black holes. The spin parameter of SWIFT J1753.5-0127 and GRO J1655-40 are estimated by modelling the strong reflection signatures present in their XMM-Newton observations. Using a newly developed, self-consistent reflection model which includes the blackbody radiation of the disk as well as the effect of Comptonisation, blurred with a relativistic line function, we infer the spin parameter of SWIFT J1753.5-0127 to be 0.76 +0.11-0.15. The inclination of this system is estimated at 55+2-7 degrees. For GRO J1655-40 we find that the disk is significantly misaligned to the orbital plane, with an innermost inclination of 30+5-10 degrees. Allowing the inclination to be a free parameter we find a lower limit for the spin of 0.90, this value increases to that of a maximal rotating black hole when the inclination is set to that of the orbital plane of J1655-40. Our technique is independent of the black hole mass and distance, uncertainties in which are among the main contributors to the spin uncertainty in previous works.
Type I X-ray bursts and superbursts from accreting neutron stars illuminate the accretion disk and produce a reflection signal that evolves as the burst fades. Examining the evolution of reflection features in the spectra will give insight into the burst-disk interaction, a potentially powerful probe of accretion disk physics. At present, reflection has been observed during only two bursts of exceptional duration. We investigate the detectability of reflection signatures with four of the latest well-studied X-ray observatory concepts: Hitomi, NICER, Athena, and LOFT. Burst spectra are modeled …
We analyse RXTE/PCA X-ray spectra of the binary X-ray pulsar Her X-1/HZ Her during short high state and one binary orbit in the preceding low state, just before short high turn-on. The spectrum is well described by two continuum components (absorbed and unabsorbed). The resulting spectral parameters are modulated with orbital phase. During low state a significant component of the flux, and its spectrum, is consistent with X-ray reflection off the face of the companion star HZ Her. This component has a significantly harder X-ray spectrum than the rest of the flux from the Her X-1 system. A seco…
From reflection to scattering: Polarimetric signatures of funnel-type outflows. Modeling obscured ultraluminous X-ray sources
University of Turku（图尔库大学）；KTH Royal Institute of Technology and Stockholm University（瑞典皇家理工学院和斯德哥尔摩大学）；Nordita（北欧理论天体物理学研究所）；Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Space Research Institute (IKI)（空间研究所（IKI））；University of Oxford（牛津大学）
Fairall 9 is one of several type 1 active galactic nuclei for which it has been claimed that the angular momentum (or spin) of the supermassive black hole can be robustly measured, using the Fe K$α$ emission line and Compton-reflection continuum in the X-ray spectrum. The method rests upon the interpretation of the Fe K$α$ line profile and associated Compton-reflection continuum in terms of relativistic broadening in the strong gravity regime in the innermost regions of an accretion disc, within a few gravitational radii of the black hole. Here, we re-examine a Suzaku X-ray spectrum of Fairall…
We present a generally applicable formalism for modeling the emission, absorption, reflection, and reprocessing of radiation by moving plasma streams close to a Kerr Black hole. The formalism can be used to investigate the observational signatures of a wide range of phenomena, including: (i) the reflection of coronal X-ray radiation off plasma plunging from the inner edge of a black hole accretion disk towards the black hole; (ii) the reflection of coronal X-ray emission off the upper layers of a geometrically thick accretion flow; (iii) the illumination of the accretion disk by a corona movin…
Collisionless shocks are efficient particle accelerators. At Earth, ions with energies exceeding 100 keV are seen upstream of the bow shock when the magnetic geometry is quasi-parallel, and large-scale supernova remnant shocks can accelerate ions into cosmic rays energies. This energization is attributed to diffusive shock acceleration, however, for this process to become active the ions must first be sufficiently energized. How and where this initial acceleration takes place has been one of the key unresolved issues in shock acceleration theory. Using Cluster spacecraft observations, we study…
Recently, two of us have found numerically rotating Ellis wormholes as solutions of 4-dimensional Einstein gravity coupled to a phantom field. In this paper, we investigate possible observational signatures to identify similar objects in the Universe. These symmetric wormholes have a mass and are compact, so they may look like black holes. We study the iron line profile in the X-ray reflection spectrum of a thin accretion disk around rotating Ellis wormholes and we find some specific observational signatures that can be used to distinguish these objects from Kerr black holes. We simulate some …
In our previous work we investigated the effect of the hypothetical reflecting boundary near the black hole event horizon on the waveform from extreme mass-ratio inspirals (EMRIs). Even if the reflection efficiency is not extremely high, we found that a significant modification of the waveform can be expected. Then, the question is how to implement the search for this signature in the actual data analysis of future space gravitational wave antennas, such as LISA. In this paper we propose a simple but efficient method to detect the signature of the reflecting boundary. The interesting feature o…
We report the detection of relativistically broadened iron K alpha emission in the X-ray spectra of AGN detected in the 4Ms CDF-S. Using the Bayesian X-ray analysis (BXA) package, we fit 199 hard band (2-7 keV) selected sources in the redshift range z=0.5--4 with three models: (i) an absorbed power-law, (ii) the first model plus a narrow reflection component, and (iii) the second model with an additional relativistic broadened reflection. The Bayesian evidence for the full sample of sources selects the model with the additional broad component as being 10^5 times more probable to describe the …
We compute fully relativistic disc response functions in the case of the "lamp-post" geometry using the full observed reflection spectrum for various X-ray source heights, disc inclination, and spin values of the central black hole. Since the observed PSD is equal to the product of the intrinsic power spectrum with the "transfer function" (i.e. the Fourier transform of the disc response function), we are able to predict the observed PSDs in the case of X-ray illumination of the inner disc. The observed PSD should show a prominent dip at high frequencies and an oscillatory behaviour, with a dec…
Over the last decades X-ray spectroscopy has proven to be a powerful tool for the estimation of black hole spin and several other key parameters in dozens of AGN and black hole X-ray binaries. In this White Paper, we discuss the observational and theoretical challenges expected in the exploration, discovery, and study of astrophysical black holes in the next decade. We focus on the case of accreting black holes and their electromagnetic signatures, with particular emphasis on the measurement of the relativistic reflection component in their X-ray spectra.
X-ray reflection signatures are observed around multiple classes of accreting compact objects. Modelling these features yield important constraints on the physics of accretion disks, motivating the development of X-ray reflection models appropriate for a variety of systems and illumination conditions. Here, constant density ionized X-ray reflection models are presented for a disk irradiated with a very hard power-law X-ray spectrum (Γ< 1) and a variable high-energy cutoff. These models are then applied to the Suzaku data of the accreting X-ray pulsar LMC X-4, where very good fits are obtained …
Beyond Disk Truncation: X-ray Reverberation Signatures of an Outflowing Corona
School of Physics and Technology, Wuhan University（武汉大学物理科学与技术学院）；Newcastle University（纽卡斯尔大学）；Universitat Politècnica de Catalunya（加泰罗尼亚理工大学）；Institut d’Estudis Espacials de Catalunya（加泰罗尼亚空间研究所）
We present a broadband spectral analysis of the atoll source 4U~1636-536 observed for $\sim92$ ks with \nustar{}. The source was found to be in a low-luminosity state during this observation with $3-79 \kev{}$ X-ray luminosity of $L_{3-79 keV}=(1.03\pm0.01)\times 10^{37}$ ergs/s, assuming a distance of 6 kpc. We have identified and removed twelve type-I X-ray bursts during this observation to study the persistent emission. The continuum is well described by a thermal Comptonization model {\tt nthcomp} with $Γ\sim1.9$, $kT_{e}\sim28 \kev{}$, and $kT_{s}\sim0.9\kev{}$. The \nustar{} data reveal …
A comprehensive wideband spectral analysis of the brightest black hole X-ray binary 4U $1543-47$ during its 2021 outburst is carried out for the first time using NICER, NuSTAR, and AstroSat observations by phenomenological and reflection modelling. The source attains a super-Eddington peak luminosity and remains in the soft state, with a small fraction ($< 3\%$) of the inverse-Comptonized photons. The spectral modelling reveals a steep photon index ($Γ\sim 2-2.6$) and relatively high inner disk temperature ($T_{in}\sim 0.9-1.27$ keV). The line-of-sight column density varies between ($0.45-0.54…
We confirm that the spectra are best fit by a model containing two Compton reflection components, one from distant material, and the other displaying relativistic broadening, most likely from the inner accretion disk. The degree of relativistic broadening indicates a preference for high black hole spin, but the reflection is weaker than that expected for a flat disk illuminated by a point source. We investigate the Compton reflection signatures as a function of luminosity, redshift and obscuration, confirming an X-ray Baldwin effect for both the narrow and broad components of the iron line. An…
We present results from Suzaku and Swift observations of the nearby radio galaxy 3C 33, and investigate the nature of absorption, reflection, and jet production in this source. We model the 0.5-100 keV nuclear continuum with a power law that is transmitted either through one or more layers of pc-scale neutral material, or through a modestly ionized pc-scale obscurer. The standard signatures of reflection from a neutral accretion disk are absent in 3C 33: there is no evidence of a relativistically blurred Fe K$α$ emission line, and no Compton reflection hump above 10 keV. We find the upper limi…
We have calculated the relativistic reflection component of the X-ray spectra of accretion disks in active galactic nuclei (AGN). Our calculations have shown that the spectra can be significantly modified by the motion of the accretion flow and the gravity and rotation of the central black hole. The absorption edges in the spectra suffer severe energy shifts and smearing, and the degree of distortion depends on the system parameters, in particular, the inner radius of the accretion disk and the disk viewing inclination angles. The effects are significant. Fluorescent X-ray emission lines from …
"Changing look" Active Galactic Nuclei (AGN) are a subset of Seyfert galaxies characterized by rapid transitions between Compton-thin and Compton-thick regimes. In their Compton-thin state, the central engine is less obscured, hence spectroscopy or timing observations can probe their innermost structures. However, it is not clear if the observed emission features and the Compton hump are associated with relativistic reflection onto the accretion disc, or complex absorption by distant, absorbing gas clouds passing by the observer's line-of-sight. Here, we investigate these two scenarios under t…
