scholarly journals Nuclear γ-ray emission from very hot accretion flows

2019 ◽  
Vol 623 ◽  
pp. A174
Author(s):  
E. Kafexhiu ◽  
F. Aharonian ◽  
M. Barkov
Keyword(s):  
Black Hole ◽  
Chemical Composition ◽  
Nuclear Reactions ◽  
High Energy ◽  
Stable Orbit ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Solar Composition ◽  
Γ Ray ◽  
Radial Evolution

Optically thin accretion plasmas can reach ion temperatures Ti ≥ 1010 K and thus trigger nuclear reactions. Using a large nuclear interactions network, we studied the radial evolution of the chemical composition of the accretion flow toward the black hole and computed the emissivity in nuclear γ-ray lines. In the advection dominated accretion flow (ADAF) regime, CNO and heavier nuclei are destroyed before reaching the last stable orbit. The overall luminosity in the de-excitation lines for a solar composition of plasma can be as high as few times 10−5 the accretion luminosity (Ṁc2) and can be increased for heavier compositions up to 10−3. The efficiency of transformation of the kinetic energy of the outflow into high energy (≥100 MeV) γ-rays through the production and decay of π0-mesons can be higher, up to 10−2 of the accretion luminosity. We show that in the ADAF model up to 15% of the mass of accretion matter can “evaporate” in the form of neutrons.

OBSERVATIONAL CONSTRAINTS ON STRONG GRAVITY

2011 ◽  
Vol 20 (14) ◽  
pp. 2755-2760
Author(s):  
CHRIS DONE
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Field ◽  
Field Tests ◽  
High Energy ◽  
Observational Constraints ◽  
Tests Of General Relativity ◽  
Strong Gravity ◽  
Accretion Flows ◽  
Spacetime Curvature

Accretion onto a black hole transforms the darkest objects in the universe to the brightest. The high energy radiation emitted from the accretion flow before it disappears forever below the event horizon lights up the regions of strong spacetime curvature close to the black hole, enabling strong field tests of General Relativity. I review the observational constraints on strong gravity from such accretion flows, and show how the data strongly support the existence of such fundamental General Relativistic features of a last stable orbit and the event horizon. However, these successes also imply that gravity does not differ significantly from Einstein's predictions above the event horizon, so any new theory of quantum gravity will be very difficult to test.

scholarly journals A New Chapter in Hard X-rays of the M87 AGN

Proceedings ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 9
Author(s):  
Ka-Wah Wong ◽  
Rodrigo S. Nemmen ◽  
Jimmy A. Irwin ◽  
Dacheng Lin
Keyword(s):  
High Energy ◽  
X Rays ◽  
X Ray ◽  
Accretion Flow ◽  
Relativistic Jet ◽  
Very High Energy ◽  
Γ Ray ◽  
High Energy Emission ◽  
First Time ◽  
Very High

The nearby M87 hosts an exceptional relativistic jet. It has been regularly monitored in radio to TeV bands, but little has been done in hard X-rays ≳10 keV. For the first time, we have successfully detected hard X-rays up to 40 keV from its X-ray core with joint Chandra and NuSTAR observations, providing important insights to the X-ray origins: from the unresolved jet or the accretion flow. We found that the hard X-ray emission is significantly lower than that predicted by synchrotron self-Compton models introduced to explain very-high-energy γ -ray emission above a GeV. We discuss recent models to understand these high energy emission processes.

scholarly journals OBSERVATIONS OF MICROQUASAR CANDIDATES WITH THE MAGIC TELESCOPE

2008 ◽  
Vol 17 (10) ◽  
pp. 1859-1866
Author(s):  
◽  
J. RICO
Keyword(s):  
Black Hole ◽  
Experimental Evidence ◽  
Energy Band ◽  
High Energy ◽  
Time Dependent ◽  
X Ray ◽  
Orbital Cycles ◽  
Very High Energy ◽  
Γ Ray ◽  
Very High

We report on the results from the observations in very high energy band (VHE, Eγ ≥ 100 GeV ) of the γ-ray binary LS I +61 303 and the black hole X-ray binary (BHXB) Cygnus X-1. LS I +61 303 was recently discovered at VHE by MAGIC1 and here we present the preliminary results from an extensive observation campaign, comprising 112 observation hours covering 4 orbital cycles, aiming at determining the time-dependent features of the VHE emission. Cygnus X-1 was observed for a total of 40 hours during 26 nights, spanning the period between June and November 2006. We report on the results of the searches for steady and variable γ-ray signals from Cygnus X-1, including the first experimental evidence for an intense flare, of duration between 1.5 and 24 hours.

ON THE NATURE OF THE X-RAY CORONA OF BLACK HOLE BINARIES

2012 ◽  
Vol 08 ◽  
pp. 73-83 ◽  
Author(s):  
JULIEN MALZAC
Keyword(s):  
Black Hole ◽  
High Energy ◽  
State Transitions ◽  
Physical Parameters ◽  
X Ray ◽  
Black Hole Binaries ◽  
Accretion Flow ◽  
Recent Developments ◽  
Hard State ◽  
Radiation Processes

We discuss the nature of the X-ray emitting plasma of black hole binaries. It is well known that the temperature and optical depth of the Comptonising electrons of the X-ray corona of black hole binaries can be measured using spectroscopy in the 1 keV-1 MeV energy band. We emphasize recent developments in the modeling of high energy radiation processes which allow us to constrain other important physical parameters of the corona, such as the strength of magnetic field, or the temperature of the ions. The results appear to challenge current accretion models. In particular, standard advection dominated accretion flow do not match the observed properties of bright hard state X-ray binaries such as Cygnus X-1 or GX 339-4. On the other hand, we find that all the data would be consistent with a multi-zone magnetically dominated hot accretion flow model. We also emphasize that besides the usual spectral state transitions observed at luminosities above a few percent of Eddington, there is observational evidence for at least two additional, more subtle, radiative transitions occuring at lower luminosities.

NUCLEAR PHOTON SCIENCE WITH INVERSE-COMPTON SCATTERING

2009 ◽  
Vol 18 (10) ◽  
pp. 1970-1975
Author(s):  
MAMORU FUJIWARA
Keyword(s):  
Materials Science ◽  
Nuclear Reactions ◽  
Short Pulse ◽  
Medical Science ◽  
High Energy ◽  
Hadron Structure ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Γ Ray ◽  
New Research

Recent developments of the synchroton radiation facilities and intense lasers are now guiding us to a new research frontier with probes of a high energy GeV photon beam and an intense and short pulse MeV γ-ray beam. New directions of the science developments with photo-nuclear reactions are discussed. The inverse Compton γ -ray has two good advantages for searching for a microscopic quantum world; they are 1) good emmitance and 2) high linear and circular polarizations. With these advantages, photon beams in the energy range from MeV to GeV are used for studying hadron structure, nuclear structure, astrophysics, materials science, as well as for applying medical science.

scholarly journals GRS 1915+105 “celebrates its majority” (1992–2010)

2010 ◽  
Vol 6 (S275) ◽  
pp. 270-274
Author(s):  
Alberto J. Castro-Tirado
Keyword(s):  
Black Hole ◽  
Radio Galaxies ◽  
High Energy ◽  
Accretion Disc ◽  
Γ Ray ◽  
High Energy Particles ◽  
Travel Distances ◽  
Open Issues

AbstractOver the 18 years since its discovery, GRS 1915+105 has continuously brightened in the X/γ-ray sky. It is considered the prototypical microquasar. Most of these are LMXBs that show sporadic ejection of matter at apparently superluminal velocities. In these the three basic ingredients of quasars are found: a black hole, an accretion disc and collimated jets of high energy particles, but in microquasars the black hole is only a few M⊙ instead of several × 106 M⊙; the accretion disc had mean thermal temperature of several × 106 K instead of several × 103 K, and the particles ejected at relativistic speeds travel distances of a few ly only, compared to few × 106 ly as in radio galaxies. However many open issues remain to be addressed.

scholarly journals Magnetohydrodynamics Simulations of Active Galactic Nucleus Disks and Jets

2020 ◽  
Vol 58 (1) ◽  
pp. 407-439
Author(s):  
Shane W. Davis ◽  
Alexander Tchekhovskoy
Keyword(s):  
Black Hole ◽  
Accretion Disk ◽  
Surrounding Medium ◽  
Observational Constraints ◽  
Disk Model ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Black Hole Spin ◽  
Spiral Density Waves ◽  
Mhd Simulations

There is a broad consensus that accretion onto supermassive black holes and consequent jet formation power the observed emission from active galactic nuclei (AGNs). However, there has been less agreement about how jets form in accretion flows, their possible relationship to black hole spin, and how they interact with the surrounding medium. There have also been theoretical concerns about instabilities in standard accretion disk models and lingering discrepancies with observational constraints. Despite seemingly successful applications to X-ray binaries, the standard accretion disk model faces a growing list of observational constraints that challenge its application to AGNs. Theoretical exploration of these questions has become increasingly reliant on numerical simulations owing to the dynamic nature of these flows and the complex interplay between hydrodynamics, magnetic fields, radiation transfer, and curved spacetime. We conclude the following: ▪  The advent of general relativistic magnetohydrodynamics (MHD) simulations has greatly improved our understanding of jet production and its dependence on black hole spin. ▪  Simulation results show both disks and jets are sensitive to the magnetic flux threading the accretion flow as well as possible misalignment between the angular momentum of the accretion flow and the black hole spin. ▪  Radiation MHD simulations are providing new insights into the stability of luminous accretion flows and highlighting the potential importance of radiation viscosity, UV opacity from atoms, and spiral density waves in AGNs.

scholarly journals 11.9. Jets from time-dependent accretion flows onto a black hole

1998 ◽  
Vol 184 ◽  
pp. 473-474
Author(s):  
Koji Nobuta ◽  
Tomoyuki Hanawa
Keyword(s):  
Black Hole ◽  
Numerical Simulations ◽  
Time Dependent ◽  
Accretion Flows ◽  
Γ Rays ◽  
Γ Ray

It is widely believed that accretion onto a black hole is the origin of X- and γ-ray emission and jets emerging from AGNs. Since the X- and γ-rays are highly variable, the accretion is also expected to be variable. We investigate highly variable hydrodynamical accretion with numerical simulations.

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