scholarly journals Blazars: Clues to Jet Physics

1999 ◽  
Vol 194 ◽  
pp. 113-122
Author(s):  
Rita M. Sambruna
Keyword(s):  
Thermal Emission ◽  
Jet Physics ◽  
Spectral Energy ◽  
Jet Formation ◽  
Ionized Gas ◽  
Extragalactic Jets ◽  
Radiative Power ◽  
Crucial Information ◽  
Γ Rays ◽  
Jet Structure

Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how energy is extracted from the central black hole. Crucial information about jet structure is provided by the spectral energy distributions from radio to γ-rays, their trends with luminosity, and correlated multifrequency variability. Since blazar jets have broad implications for all radio-loud (and possibly radio-quiet) AGNs, we also need to understand their circumnuclear structure, especially the details of the physical and dynamical conditions of the highly ionized gas on sub-pc scales, which could be directly related to jet formation and radiative power. Eventually, the bulk of information provided by blazars will help us clarify the origin of the radio-loud/radio-quiet AGN dichotomy, one of the most outstanding open issues of extragalactic astrophysics.

scholarly journals Massive stars at (very) high energies: γ-ray binaries

2010 ◽  
Vol 6 (S272) ◽  
pp. 581-586
Author(s):  
Guillaume Dubus ◽  
Benoît Cerutti
Keyword(s):  
High Energy Physics ◽  
Thermal Emission ◽  
Compact Object ◽  
High Energy ◽  
Be Stars ◽  
Radiative Power ◽  
Very High Energy ◽  
Γ Rays ◽  
Γ Ray ◽  
Very High

Abstractγ-ray binaries are systems that emit most of their radiative power above 1 MeV. They are associated with O or Be stars in orbit with a compact object, possibly a young pulsar. Much like colliding wind binaries, the pulsar generates a relativistic wind that interacts with the stellar wind. The result is non-thermal emission from radio to very high energy γ-rays. The wind, radiation and magnetic field of the massive star play a major role in the dynamics and radiative output of the system. They are particularly important to understand the high energy physics at work. Inversely, γ-ray binaries offer novel probes of stellar winds and insights into the fate of O/B binaries.

scholarly journals Powerful extragalactic jets dissipate their kinetic energy far from the central black hole

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Adam Leah W. Harvey ◽  
Markos Georganopoulos ◽  
Eileen T. Meyer
Keyword(s):  
Black Hole ◽  
Energy Dissipation ◽  
Kinetic Energy ◽  
Gamma Ray ◽  
Spectral Energy ◽  
Jet Formation ◽  
A Value ◽  
Line Region ◽  
Extragalactic Jets ◽  
Jet Collimation

Abstract Accretion onto the supermassive black hole in some active galactic nuclei (AGN) drives relativistic jets of plasma, which dissipate a significant fraction of their kinetic energy into gamma-ray radiation. The location of energy dissipation in powerful extragalactic jets is currently unknown, with implications for particle acceleration, jet formation, jet collimation, and energy dissipation. Previous studies have been unable to constrain the location between possibilities ranging from the sub-parsec-scale broad-line region to the parsec-scale molecular torus, and beyond. Here we show using a simple diagnostic that the more distant molecular torus is the dominant location for powerful jets. This diagnostic, called the seed factor, is dependent only on observable quantities, and is unique to the seed photon population at the location of gamma-ray emission. Using 62 multiwavelength, quasi-simultaneous spectral energy distributions of gamma-ray quasars, we find a seed factor distribution which peaks at a value corresponding to the molecular torus, demonstrating that energy dissipation occurs  ~1 parsec from the black hole (or  ~104 Schwarzchild radii for a 109M⊙ black hole).

Investigating the multiband non-thermal emission of the 100 TeV source eHWC J2019+368 with a pulsar wind nebula scenario

2020 ◽  
Vol 498 (4) ◽  
pp. 4901-4905
Author(s):  
Jun Fang ◽  
Lu Wen ◽  
Huan Yu ◽  
Songzhan Chen
Keyword(s):  
Energy Distribution ◽  
Power Law ◽  
Thermal Emission ◽  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
Recent Measurement ◽  
Inverse Compton Scattering ◽  
Γ Rays ◽  
Pulsar Wind

ABSTRACT eHWC J2019+368 is one of the sources emitting γ-rays with energies higher than 100 TeV based on the recent measurement with the High Altitude Water Cherenkov Observatory (HAWC), and the origin is still in debate. The pulsar PSR J2021+3651 is spatially coincident with the TeV source. We investigate theoretically whether the multiband non-thermal emission of eHWC J2019+368 can originate from the pulsar wind nebula (PWN) G75.2+0.1 powered by PSR J2021+3651. In the model, the spin-down power of the pulsar is transferred to high-energy particles and magnetic field in the nebula. As the particles with an energy distribution of either a broken power law or a power law continually injected into the nebula, the multiband non-thermal emission is produced via synchrotron radiation and inverse Compton scattering. The spectral energy distribution of the nebula from the model with the reasonable parameters is generally consistent with the detected radio, X-ray, and TeV γ-ray fluxes. Our study supports that the PWN has the ability to produce the TeV γ-rays of eHWC J2019+368, and the most energetic particles in the nebula have energies up to about 0.4 PeV.

Non-thermal emission from the interaction of extragalactic jets with stars

2017 ◽  
Author(s):  
F. L. Vieyro ◽  
N. Torres-Albà ◽  
V. Bosch-Ramon
Keyword(s):  
Thermal Emission ◽  
Extragalactic Jets

scholarly journals The limb-brightened jet of M87 down to the 7 Schwarzschild radii scale

2018 ◽  
Vol 616 ◽  
pp. A188 ◽  
Author(s):  
J.-Y. Kim ◽  
T. P. Krichbaum ◽  
R.-S. Lu ◽  
E. Ros ◽  
U. Bach ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Angular Resolution ◽  
Magnetic Energy ◽  
Large Mass ◽  
High Angular Resolution ◽  
Data Sets ◽  
Jet Formation ◽  
Physical Conditions ◽  
Self Similar ◽  
Jet Structure

Messier 87 (M 87) is one of the nearest radio galaxies with a prominent jet extending from sub-pc to kpc scales. Because of its proximity and the large mass of its central black hole (BH), it is one of the best radio sources for the study of jet formation. We study the physical conditions near the jet base at projected separations from the BH of ~7–100 Schwarzschild radii (Rsch). Global mm-VLBI Array (GMVA) observations at 86 GHz (λ = 3.5 mm) provide an angular resolution of ~50 μas, which corresponds to a spatial resolution of only 7 Rsch and reach the small spatial scale. We use five GMVA data sets of M 87 obtained from 2004 to 2015 and present new high angular resolution VLBI maps at 86 GHz. In particular, we focus on the analysis of the brightness temperature, the jet ridge lines, and the ratio of jet to counter-jet. The imaging reveals a parabolically expanding limb-brightened jet which emanates from a resolved VLBI core of ~(8–13) Rsch in size. The observed brightness temperature of the core at any epoch is ~(1–3) × 1010 K, which is below the equipartition brightness temperature and suggests magnetic energy dominance at the jet base. We estimate the diameter of the jet at its base to be ~5 Rsch assuming a self-similar jet structure. This suggests that the sheath of the jet may be anchored in the very inner portion of the accretion disk. The image stacking reveals faint emission at the center of the edge-brightened jet on sub-pc scales. We discuss its physical implication within the context of the spine-sheath structure of the jet.

scholarly journals Relating grain size distributions in circumstellar discs to the spectral index at millimetre wavelengths

2020 ◽  
Vol 641 ◽  
pp. A75
Author(s):  
T. Löhne
Keyword(s):  
Size Dependence ◽  
Thermal Emission ◽  
Circumstellar Dust ◽  
Spectral Energy ◽  
Size Distributions ◽  
Energy Distributions ◽  
Erosion Processes ◽  
Grain Size Distributions ◽  
Small Grains ◽  
Insufficient Knowledge

The excess emission seen in spectral energy distributions (SEDs) is commonly used to infer the properties of the emitting circumstellar dust in protoplanetary and debris discs. Most notably, dust size distributions and details of the collision physics are derived from SED slopes at long wavelengths. This paper reviews the approximations that are commonly used and contrasts them with numerical results for the thermal emission. The inferred size distribution indexes p are shown to be greater and more sensitive to the observed sub(mm) spectral indexes, αmm, than previously considered. This effect results from aspects of the transition from small grains with volumetric absorption to bigger grains that absorb and emit near to their surface, controlled by both the real and the imaginary part of the refractive index. The steeper size distributions indicate stronger size-dependence of material strengths or impact velocities or, otherwise, less efficient transport or erosion processes. Strong uncertainties remain because of insufficient knowledge of the material composition, porosity, and optical properties at long wavelengths.

scholarly journals NIKA2 observations around LBV stars Emission from stars and circumstellar material

2020 ◽  
Vol 228 ◽  
pp. 00023
Author(s):  
J. Ricardo Rizzo ◽  
Alessia Ritacco ◽  
Cristobal Bordiu
Keyword(s):  
Thermal Emission ◽  
Continuum Emission ◽  
Core Collapse ◽  
Spectral Indices ◽  
Ionized Gas ◽  
Dark Cloud ◽  
High Frequencies ◽  
Circumstellar Material ◽  
Dark Clouds ◽  
Luminous Blue Variable

Luminous Blue Variable (LBV) stars are evolved massive objects, previous to core-collapse supernova. LBVs are characterized by photometric and spectroscopic variability, produced by strong and dense winds, mass-loss events and very intense UV radiation. LBVs strongly disturb their surroundings by heating and shocking, and produce important amounts of dust. The study of the circumstellar material is therefore crucial to understand how these massive stars evolve, and also to characterize their effects onto the interstellar medium. The versatility of NIKA2 is a key in providing simultaneous observations of both the stellar continuum and the extended, circumstellar contribution. The NIKA2 frequencies (150 and 260 GHz) are in the range where thermal dust and free-free emission compete, and hence NIKA2 has the capacity to provide key information about the spatial distribution of circumstellar ionized gas, warm dust and nearby dark clouds; non-thermal emission is also possible even at these high frequencies. We show the results of the first NIKA2 survey towards five LBVs. We detected emission from four stars, three of them immersed in tenuous circumstellar material. The spectral indices show a complex distribution and allowed us to separate and characterize different components. We also found nearby dark clouds, with spectral indices typical of thermal emission from dust. Spectral indices of the detected stars are negative and hard to be explained only by free-free processes. In one of the sources, G79.29+0.46, we also found a strong correlation of the 1mm and 2mm continuum emission with respect to nested molecular shells at ≈1 pc from the LBV. The spectral index in this region clearly separates four components: the LBV star, a bubble characterized by free-free emission, and a shell interacting with a nearby infrared dark cloud.

scholarly journals From grains to pebbles: the influence of size distribution and chemical composition on dust emission properties

2019 ◽  
Vol 631 ◽  
pp. A88 ◽  
Author(s):  
N. Ysard ◽  
M. Koehler ◽  
I. Jimenez-Serra ◽  
A. P. Jones ◽  
L. Verstraete
Keyword(s):  
Chemical Composition ◽  
Size Distribution ◽  
Spectral Index ◽  
Thermal Emission ◽  
Spectral Energy ◽  
Internal Source ◽  
Dust Grains ◽  
Grain Composition ◽  
Dust Mass ◽  
Dust Composition

Context. The size and chemical composition of interstellar dust grains are critical in setting the dynamical, physical, and chemical evolution of all the media in which they are present. Thanks to facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA) and, in the future, the Square Kilometer Array (SKA), thermal emission in the (sub)millimetre to centimetre domain has become a very convenient way to trace grain properties. Aims. Our aim is to understand the influence of the composition and size distribution of dust grains on the shape of their spectral energy distribution (peak position, spectral index) in dense interstellar regions such as molecular clouds, prestellar cores, young stellar objects, and protoplanetary discs. Methods. Starting from the optical constants defined in The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS) for amorphous hydrogenated carbon grains and amorphous silicates in addition to water ice, we defined six material mixtures that we believe are representative of the expected dust composition in dense interstellar regions. The optical properties of 0.01 μm to 10 cm grains were then calculated with effective medium and Mie theories. The corresponding spectral energy distributions were subsequently calculated for isolated clouds either externally heated by the standard interstellar radiation field alone or in addition to an internal source. Results. The three main outcomes of this study are as follows. Firstly, the dust mass absorption coefficient strongly depends on both grain composition and size distribution potentially leading to errors in dust mass estimates by factors up to ~3 and 20, respectively. Secondly, it appears almost impossible to retrieve the grain composition from the (sub)millimetre to centimetre thermal emission shape alone as its spectral index for λ ≳ 3 mm does not depend on dust composition. Thirdly, using the “true” dust opacity spectral index to estimate grain sizes may lead to erroneous findings as the observed spectral index can be highly modified by the dust temperature distribution along the line of sight, which depends on the specific heating source and on the geometry of the studied interstellar region. Conclusions. Based on the interpretation of only the spectral shape of (sub)millimetre to centimetre observational data, the determination of the dust masses, compositions, and sizes are highly uncertain.

scholarly journals Thermal emission from the amorphous dust: An alternative possibility of the origin of the anomalous microwave emission

2019 ◽  
Vol 72 (1) ◽  
Author(s):  
Masashi Nashimoto ◽  
Makoto Hattori ◽  
Ricardo Génova-Santos ◽  
Frédérick Poidevin
Keyword(s):  
Interstellar Dust ◽  
Amorphous Materials ◽  
Thermal Emission ◽  
Far Infrared ◽  
Alternative Interpretation ◽  
Microwave Emission ◽  
Spectral Energy ◽  
Radiative Processes ◽  
Resonance Emission ◽  
Amorphous Silicate

Abstract Complete studies of the radiative processes of thermal emission from the amorphous dust from microwave through far-infrared wavebands are presented by taking into account, self-consistently for the first time, the standard two-level systems (TLS) model of amorphous materials. The observed spectral energy distributions (SEDs) for the Perseus molecular cloud (MC) and W 43 from microwave through far-infrared are fitted with the SEDs calculated with the TLS model of amorphous silicate. We have found that the model SEDs reproduce the observed properties of the anomalous microwave emission (AME) well. The present result suggests an alternative interpretation for the AME being carried by the resonance emission of the TLS of amorphous materials without introducing new species. Simultaneous fitting of the intensity and polarization SEDs for the Perseus MC and W 43 are also performed. The amorphous model reproduces the overall observed feature of the intensity and polarization SEDs of the Perseus MC and W 43. However, the model’s predicted polarization fraction of the AME is slightly higher than the QUIJOTE upper limits in several frequency bands. A possible improvement of our model to resolve this problem is proposed. Our model predicts that interstellar dust is amorphous materials with very different physical characteristics compared with terrestrial amorphous materials.

scholarly journals Non-thermal emission in radio galaxy lobes – II. Centaurus A, Centaurus B, and NGC 6251

2019 ◽  
Vol 490 (2) ◽  
pp. 1489-1497 ◽  
Author(s):  
Massimo Persic ◽  
Yoel Rephaeli
Keyword(s):  
Thermal Emission ◽  
Background Radiation ◽  
Spectral Energy Distribution ◽  
Recent Analysis ◽  
Spectral Energy ◽  
Energetic Proton ◽  
X Ray ◽  
Radiation Fields ◽  
Γ Ray ◽  
Centaurus A

ABSTRACT Radio and γ-ray measurements of large lobes of several radio galaxies provide adequate basis for determining whether emission in these widely separated spectral regions is largely by energetic electrons. This is very much of interest as there is of yet no unequivocal evidence for a significant energetic proton component to account for γ-ray emission by neutral pion decay. A quantitative assessment of the pion yield spectral distribution necessitates full accounting of the local and background radiation fields in the lobes; indeed, doing so in our recent analysis of the spectral energy distribution of the Fornax A lobes considerably weakened previous conclusions on the hadronic origin of the emission measured by the Fermi satellite. We present the results of similar analyses of the measured radio, X-ray, and γ-ray emission from the lobes of Centaurus A, Centaurus B, and NGC 6251. The results indicate that the measured γ-ray emission from these lobes can be accounted for by Compton scattering of the radio-emitting electrons off the superposed radiation fields in the lobes; consequently, we set upper bounds on the energetic proton contents of the lobes.

Sign in / Sign up

Export Citation Format

Share Document