Search results for "Black hole physics"
showing 10 items of 24 documents
First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
2019
The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring rad…
On Relativistic Disk Spectroscopy in Compact Objects with X-ray CCD Cameras
2010
X-ray charge-coupled devices (CCDs) are the workhorse detectors of modern X-ray astronomy. Typically covering the 0.3-10.0 keV energy range, CCDs are able to detect photoelectric absorption edges and K shell lines from most abundant metals. New CCDs also offer resolutions of 30-50 (E/dE), which is sufficient to detect lines in hot plasmas and to resolve many lines shaped by dynamical processes in accretion flows. The spectral capabilities of X-ray CCDs have been particularly important in detecting relativistic emission lines from the inner disks around accreting neutron stars and black holes. One drawback of X-ray CCDs is that spectra can be distorted by photon "pile-up", wherein two or mor…
First M87 Event Horizon Telescope Results. II. Array and Instrumentation
2019
The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ~1.3 mm, EHT angular resolution (λ/D) is ~25 μas, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of th…
On the nature of the soft γ-ray emission in the hard state of the black hole transient GRS 1716-249
2020
The black hole transient GRS 1716-249 was monitored from the radio to the gamma-ray band during its 2016-2017 outburst. This paper focuses on the Spectral Energy Distribution (SED) obtained in 2017 February-March, when GRS 1716-249 was in a bright hard spectral state. The soft gamma-ray data collected with the INTEGRAL/SPI telescope show the presence of a spectral component which is in excess of the thermal Comptonisation emission. This component is usually interpreted as inverse Compton emission from a tiny fraction of non-thermal electrons in the X-ray corona. We find that hybrid thermal/non-thermal Comptonisation models provide a good fit to the X/gamma-ray spectrum of GRS 1716-249. The …
Accrétion et éjection dans les systèmes binaires X transitoires à trous noirs : le cas de GRS 1716-249
2020
I buchi neri transienti (BHT) sono tra le sorgenti con emissione ai raggi X più luminose della galassia. Grazie all’elevato flusso in banda X e alla loro alta variabilità temporale. queste sorgenti offrono un’opportunità unica per studiare la fisica dell’accrescimento in straordinareie condizioni fisiche. I BHT mostrano episodici outburst caratterizzati da diverse luminosità in banda X e γ, diverse forme spettrali e proprietà della variabilità temporale. L’obiettivo di questa tesi è lo studio della geometria, dei meccanismi e dei processi fisici coinvolti nell’emissione del buco nero transiente GRS 716-249. Di seguito presento l’analisi spettrale e temporale delle osservazioni della GRS 171…
First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
2019
We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of ~40 μas, consistent with the size and shape of the lensed photon orbit encircling the "shadow" of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others' work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to av…
The jets and disc of SS 433 at super-Eddington luminosities
2009
We examine the jets and the disc of SS 433 at super-Eddington luminosities with 600 times Eddington critical accretion rate by time-dependent two-dimensional radiation hydrodynamical calculations, assuming alpha-model for the viscosity. One-dimensional supercritical accretion disc models with mass loss or advection are used as the initial configurations of the disc. As a result, from the initial advective disc models with alpha =0.001 and 0.1, we obtain the total luminosities 2.5x10^{40} and 2.0x10^{40} erg/s. The total mass-outflow rates are 4x10^{-5} and 10^{-4} solar-mass/yr and the rates of the relativistic axial outflows in a small half opening angle of 1 degree are about 10^{-6} solar…
Black-Hole Accretion Discs and Jets at Super-Eddington Luminosity
2004
Super-Eddington accretion discs with 3 and 15 dot M_E around black holes with mass 10 M_sun are examined by two-dimensional radiation hydrodynamical calculations extending from the inner disc edge to 5*10^4 r_g and lasting up to \sim 10^6 r_g/c. The dominant radiation-pressure force in the inner region of the disc accelerates the gas vertically to the disc plane, and jets with 0.2 -- 0.4$c$ are formed along the rotational axis. In the case of the lower accretion rate, the initially anisotropic high-velocity jet expands outward and becomes gradually isotropic flow in the distant region. The mass-outflow rate from the outer boundary is as large as \sim 10^{19} -- 10^{23} g s^{-1}, but it is v…
High-energy monitoring of NGC 4593 II. Broad-band spectral analysis: testing the two-corona model
2019
It is widely believed that the primary X-ray emission of AGN is due to the Comptonisation of optical-UV photons from a hot electron corona, while the origin of the 'soft-excess' is still uncertain and matter of debate. A second Comptonisation component, called warm corona, was therefore proposed to account for the soft-excess, and found in agreement with the optical-UV to X-ray emission of a sample of Seyfert galaxies. In this context, we exploit the broadband XMM-Newton and NuSTAR simultaneous observations of the Seyfert galaxy NGC 4593 to further test the so called "two corona model". The NGC 4593 spectra are well reproduced by the model, from the optical/UV to the hard X-rays. Moreover, …
A Simple Model of Radiative Emission in M87
2005
We present a simple physical model of the central source emission in the M87 galaxy. It is well known that the observed X-ray luminosity from this galactic nucleus is much lower than the predicted one, if a standard radiative efficiency is assumed. Up to now the main model invoked to explain such a luminosity is the ADAF (Advection-Dominated-Accretion-Flow) model. Our approach supposes only a simple axis-symmetric adiabatic accretion with a low angular momentum together with the bremsstrahlung emission process in the accreting gas. With no other special hypothesis on the dynamics of the system, this model agrees well enough with the luminosity value measured by Chandra.