scholarly journals Multi-wavelength torus–jet model for Sagittarius A*

2019 ◽  
Vol 624 ◽  
pp. A52
Author(s):  
F. H. Vincent ◽  
M. A. Abramowicz ◽  
A. A. Zdziarski ◽  
M. Wielgus ◽  
T. Paumard ◽  
...  
Keyword(s):  
Black Hole ◽  
Numerical Simulations ◽  
Spectral Index ◽  
Analytic Description ◽  
Emission Region ◽  
Quiescent State ◽  
Infrared Spectral ◽  
Multi Wavelength ◽  
Sgr A ◽  
Best Fit

Context. The properties of the accretion/ejection flow surrounding the supermassive central black hole of the Galaxy Sgr A* will be scrutinized by the new-generation instrument GRAVITY and the Event Horizon Telescope (EHT). Developing fast, robust, and simple models of such flows is therefore important and very timely. Aims. We want to model the quiescent emission of Sgr A* from radio to mid-infrared wavelengths, using thermal and nonthermal synchrotron. The radiation is emitted by the overlay of a magnetized compact torus close to the black hole, and a large-scale magnetized jet. We compare model spectra and images to the multi-wavelength observable constraints available to date. We simulate EHT observations at 1.3 mm of the best-fit model for different inclinations. methods. We use a simple analytic description for the geometry of the torus and jet. We model their emission by thermal synchrotron and κ-distribution synchrotron, respectively. We use relativistic ray tracing to compute simulated spectra and images, restricting our analysis to the Schwarzschild (zero spin) case. A best-fit is found by adjusting the simulated spectra to the latest observed data, and we check the consistency of our spectral best fits with the radio-image sizes and infrared spectral index constraints. We use the open-source eht-imaging library to generate EHT-reconstructed images. Results. We find perfect spectral fit ( χred2 ≈ 1) both for nearly face-on and nearly edge-on views. These best fits give parameter values very close to those found by the most recent numerical simulations, which are much more complex than our model. The intrinsic radio size of Sgr A* is found to be in reasonable agreement with the centimetric observed constraints. Our best-fit infrared spectral index is in perfect agreement with the latest constraints. Our emission region at 1.3 mm, although larger than the early-EHT Gaussian best fit, does contain bright features at the ≲40 μas scale. EHT-reconstructed images show that torus/jet-specific features persist after the reconstruction procedure, and that these features are sensitive to inclination. Conclusions. The main interest of our model is to provide a simple and fast model of the quiescent state of Sgr A*, which gives extremely similar results to those of state-of-the-art numerical simulations. Our model is easy to use and we publish all the material necessary to reproduce our spectra and images, meaning that anyone interested can use our results relatively straightforwardly. We hope that such a public tool will be useful in the context of the recent and near-future GRAVITY and EHT results.

scholarly journals The large gamma-ray flare of the flat-spectrum radio quasar PKS 0346−27

2019 ◽  
Vol 627 ◽  
pp. A140
Author(s):  
R. Angioni ◽  
R. Nesci ◽  
J. D. Finke ◽  
S. Buson ◽  
S. Ciprini
Keyword(s):  
Spectral Properties ◽  
Emission Region ◽  
Short Time Scale ◽  
Quiescent State ◽  
Emission Model ◽  
X Rays ◽  
High State ◽  
Spectrum Radio ◽  
Multi Wavelength ◽  
Radio Quasar

Aims. In this paper, we characterize the first γ-ray flaring episode of the flat-spectrum radio quasar PKS 0346−27 (z = 0.991), as revealed by Fermi-LAT monitoring data, and the concurrent multi-wavelength variability observed from radio through X-rays. Methods. We studied the long- and short-term flux and spectral variability from PKS 0346−27 by producing γ-ray light curves with different time binning. We complement the Fermi-LAT data with multi-wavelength observations from the Atacama Large Millimeter Array (radio mm-band), the Rapid Eye Mount telescope (near-infrared) and Swift (optical-UV and X-rays). This quasi-simultaneous multi-wavelength coverage allowed us to construct time-resolved spectral energy distributions (SEDs) of PKS 0346−27 and compare the broadband spectral properties of the source between different activity states using a one-zone leptonic emission model. Results. PKS 0346−27 entered an elevated γ-ray activity state starting from the beginning of 2018. The high-state continued throughout the year, displaying the highest fluxes in May 2018. We find evidence of short-time scale variability down to approximately 1.5 h, which constrains the γ-ray emission region to be compact. The extended flaring period was characterized by a persistently harder spectrum with respect to the quiescent state, indicating changes in the broadband spectral properties of the source. This was confirmed by the multi-wavelength observations, which show a shift in the position of the two SED peaks by approximately two orders of magnitude in energy and peak flux value. As a result, the non-thermal jet emission completely outshines the thermal contribution from the dust torus and accretion disk during the high state. The broadband SED of PKS 0346−27 transitions from a typical Low-Synchrotron-Peaked (LSP) to the Intermediate-Synchrotron-Peaked (ISP) class, a behavior previously observed in other flaring γ-ray sources. Our one-zone leptonic emission model of the high-state SEDs constrains the γ-ray emission region to have a lower magnetic field, larger radius, and higher maximum electron Lorentz factors with respect to the quiescent SED. Finally, we note that the bright and hard γ-ray spectrum observed during the peak of flaring activity in May 2018 implies that PKS 0346−27 could be a promising target for future ground-based Cherenkov observatories such as the Cherenkov Telescope Array (CTA). The CTA could detect such a flare in the low-energy tail of its energy range during a high state such as the one observed in May 2018.

scholarly journals Sgr A* near-infrared flares from reconnection events in a magnetically arrested disc

2020 ◽  
Vol 497 (4) ◽  
pp. 4999-5007 ◽  
Author(s):  
J Dexter ◽  
A Tchekhovskoy ◽  
A Jiménez-Rosales ◽  
S M Ressler ◽  
M Bauböck ◽  
...  
Keyword(s):  
Black Hole ◽  
Magnetic Flux ◽  
Linear Polarization ◽  
Near Infrared ◽  
Broad Class ◽  
Emission Region ◽  
Polarization Angle ◽  
Continuous Rotation ◽  
General Relativistic ◽  
Sgr A

ABSTRACT Large-amplitude Sgr A* near-infrared (NIR) flares result from energy injection into electrons near the black hole event horizon. Astrometry data show continuous rotation of the emission region during bright flares, and corresponding rotation of the linear polarization angle. One broad class of physical flare models invokes magnetic reconnection. Here, we show that such a scenario can arise in a general relativistic magnetohydrodynamic simulation of a magnetically arrested disc. Saturation of magnetic flux triggers eruption events, where magnetically dominated plasma is expelled from near the horizon and forms a rotating, spiral structure. Dissipation occurs via reconnection at the interface of the magnetically dominated plasma and surrounding fluid. This dissipation is associated with large increases in NIR emission in models of Sgr A*, with durations and amplitudes consistent with the observed flares. Such events occur at roughly the time-scale to re-accumulate the magnetic flux from the inner accretion disc, ≃10 h for Sgr A*. We study NIR observables from one sample event to show that the emission morphology tracks the boundary of the magnetically dominated region. As the region rotates around the black hole, the NIR centroid and linear polarization angle both undergo continuous rotation, similar to the behaviour seen in Sgr A* flares.

scholarly journals 10.4. Multi-wavelength VLBA mapping of Sgr A∗

1998 ◽  
Vol 184 ◽  
pp. 437-438
Author(s):  
Zhi-Qiang Shen ◽  
K. Y. Lo ◽  
Jun-Hui Zhao ◽  
Paul Ho
Keyword(s):  
Energy Source ◽  
Black Hole ◽  
Radio Source ◽  
Radio Sources ◽  
Massive Black Hole ◽  
Nonthermal Radio ◽  
The Galaxy ◽  
Multi Wavelength ◽  
Sgr A ◽  
Source Structure

Sgr A∗, the enigmatic compact nonthermal radio source located at the center of the Galaxy for many years has been considered as the signpost of a massive black hole (Rees 1982; Lo 1986; Falcke et al. 1997). Its properties are unique in the Galaxy, but it resembles other nuclear radio sources (Lo 1993). Efforts to delineate the source structure of Sgr A∗, in order to constraint the nature of the underlying energy source, have been ongoing since 1975 (Lo et al. 1975).

scholarly journals Constraining jet physics in weakly accreting black holes

2006 ◽  
Vol 2 (S238) ◽  
pp. 145-149
Author(s):  
Sera Markoff
Keyword(s):  
Black Hole ◽  
Large Scale ◽  
Galactic Center ◽  
Mass Scale ◽  
Compact Objects ◽  
Jet Physics ◽  
Accretion Rates ◽  
Test Population ◽  
Multi Wavelength ◽  
Sgr A

AbstractOutflowing jets are observed in a variety of astronomical objects such as accreting compact objects from X-ray binaries (XRBs) to active galactic nuclei (AGN), as well as at stellar birth and death. Yet we still do not know exactly what they are comprised of, why and how they form, or their exact relationship with the accretion flow. In this talk I focus on jets in black hole systems, which provide the ideal test population for studying the relationship between inflow and outflow over an extreme range in mass and accretion rate.I present several recent results from coordinated multi-wavelength studies of low-luminosity sources. These results not only support similar trends in weakly accreting black hole behavior across the mass scale, but also suggest that the same underlying physical model can explain their broadband spectra. I discuss how comparisons between small- and large-scale systems are revealing new information about the regions nearest the black hole, providing clues about the creation of these weakest of jets. Furthermore, comparisons between our Galactic center nucleus Sgr A* and other sources at slightly higher accretion rates can elucidate the processes which drive central activity, and pave the way for new tests with upcoming instruments.

scholarly journals Statistical and theoretical studies of flares from Sagittarius A⋆

2016 ◽  
Vol 11 (S322) ◽  
pp. 31-38
Author(s):  
Ya-Ping Li ◽  
Qiang Yuan ◽  
Q. Daniel Wang ◽  
P. F. Chen ◽  
Joseph Neilsen ◽  
...  
Keyword(s):  
Black Hole ◽  
Solar Flares ◽  
Galactic Center ◽  
Theoretical Models ◽  
Spatial Dimension ◽  
X Ray ◽  
Sagittarius A ◽  
Multi Wavelength ◽  
Self Organized Criticality ◽  
Sgr A

AbstractMulti-wavelength flares have routinely been observed from the supermassive black hole, Sagittarius A⋆ (Sgr A⋆), at our Galactic center. The nature of these flares remains largely unclear, despite many theoretical models. We study the statistical properties of the Sgr A⋆ X-ray flares and find that they are consistent with the theoretical prediction of the self-organized criticality system with the spatial dimension S = 3. We suggest that the X-ray flares represent plasmoid ejections driven by magnetic reconnection (similar to solar flares) in the accretion flow onto the black hole. Motivated by the statistical results, we further develop a time-dependent magnetohydrodynamic (MHD) model for the multi-band flares from Sgr A⋆ by analogy with models of solar flares/coronal mass ejections (CMEs). We calculate the X-ray, infrared flare light curves, and the spectra, and find that our model can explain the main features of the flares.

scholarly journals Dynamically important magnetic fields near the event horizon of Sgr A*

2020 ◽  
Vol 643 ◽  
pp. A56
Author(s):  
◽  
A. Jiménez-Rosales ◽  
J. Dexter ◽  
F. Widmann ◽  
M. Bauböck ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Near Infrared ◽  
Emission Region ◽  
Compact Region ◽  
Background Magnetic Field ◽  
Field Geometry ◽  
Sgr A ◽  
The One ◽  
Linear Polarisation

We study the time-variable linear polarisation of Sgr A* during a bright near-infrared flare observed with the GRAVITY instrument on July 28, 2018. Motivated by the time evolution of both the observed astrometric and polarimetric signatures, we interpret the data in terms of the polarised emission of a compact region (“hotspot”) orbiting a black hole in a fixed, background magnetic field geometry. We calculated a grid of general relativistic ray-tracing models, created mock observations by simulating the instrumental response, and compared predicted polarimetric quantities directly to the measurements. We take into account an improved instrument calibration that now includes the instrument’s response as a function of time, and we explore a variety of idealised magnetic field configurations. We find that the linear polarisation angle rotates during the flare, which is consistent with previous results. The hotspot model can explain the observed evolution of the linear polarisation. In order to match the astrometric period of this flare, the near horizon magnetic field is required to have a significant poloidal component, which is associated with strong and dynamically important fields. The observed linear polarisation fraction of ≃30% is smaller than the one predicted by our model (≃50%). The emission is likely beam depolarised, indicating that the flaring emission region resolves the magnetic field structure close to the black hole.

scholarly journals Simulations of disks in binary systems using parallelized SPH to reach extreme spatial resolution

2003 ◽  
Vol 208 ◽  
pp. 427-428
Author(s):  
D. Molteni ◽  
F. Fauci ◽  
G. Gerardi ◽  
M. A. Valenza
Keyword(s):  
Black Hole ◽  
Angular Momentum ◽  
Numerical Simulations ◽  
Spatial Resolution ◽  
Spectral Properties ◽  
Binary Systems ◽  
Compact Star ◽  
Close Binary ◽  
Gas Transfer ◽  
Set Up

Results of 3D numerical simulations of the gas transfer in close binary systems show that it is possible the production of accretion streams having low specific angular momentum in a region close to the accreting star. These streams are mainly placed above the orbital disc. The eventual formation of such bulges and shock heated flows is interesting in the context of advection dominated solutions and for the explanation of spectral properties of the Black Hole candidates in binary systems. We set up a parallelized version of 3D S.P.H. code, using domain decomposion. with increasing spatial resolution around the compact star.

scholarly journals DIRECTLY OBSERVING ENTROPY ACCUMULATION ON THE HORIZON AND HOLOGRAPHY

2012 ◽  
Vol 21 (11) ◽  
pp. 1242010
Author(s):  
ARIEL EDERY ◽  
HUGUES BEAUCHESNE
Keyword(s):  
Black Hole ◽  
Numerical Simulations ◽  
Gravitational Collapse ◽  
Spherical Symmetry ◽  
Proper Time ◽  
Horizon Area

Recent numerical simulations of gravitational collapse show that there exists a special foliation of the spacetime where matter and entropy accumulate directly on the inside of the horizon surface. In this foliation, the time coincides with the proper time of the asymptotic static observer (ASO) and for spherical symmetry, this corresponds to isotropic co-ordinates. In this gauge, the three-volume in the interior shrinks to zero and only the horizon area remains at the end of collapse. In a different foliation, matter and entropy accumulate in the volume. The entropy is however independent of the foliation. Black hole holography is therefore a mapping from an arbitrary foliation, where information resides in the volume, to the special ASO frame, where it resides directly on the horizon surface.

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