Incoherent Synchrotron Emission Research Articles

Novel explanation of the Active Galactic Nuclei. The Power Source of Quasars as a result of vacuum polarization by the gravitational singularities on the distributional BHs horizon

In this paper we argue that the current paradigm for AGN and quasars is essentially incomplete and a rivision is needed. Remind that the current paradigm for AGN and quasars is that their radio emission is explained by synchrotron radiation from relativistic electrons that are Doppler boosted through bulk motion. In this model, the intrinsic brightness temperatures cannot exceed 1011 to 1012 K. Typical Doppler boosting is expected to be able to raise this temperature by a factor of 10. The observed brightness temperature of the most compact structures in BL Lac, constrained by baselines longer than 5.3G, must indeed exceed 2 × 1013K and can reach as high as ˜ 3 × 1014K. This is difficult to reconcile with current incoherent synchrotron emission models from relativistic electrons, requiring alternative models such as emission from relativistic protons. However the proton, as we know, is 1836 times heavier than an electron and absolutely huge energy is required to accelerated it to sublight speed. These alternative models such as emission from relativistic protons can be suported by semiclassical gravity effect finds its roots in the singular behavior of quantum fields on curved distributional space- times presented by rotating gravitational singularities.

Weibel Instability in Hot Plasma Flows with the Production of Gamma-Rays and Electron–Positron Pairs

Abstract We present the results of the theoretical analysis and numerical simulations of the Weibel instability in two counterstreaming hot relativistic plasma flows, for instance the flows of electron–proton plasmas with rest-mass densities , Lorentz factors , and proper temperatures . The instability growth rate and the filament size at the linear stage are found analytically and are in qualitative agreement with the results of three-dimensional particle-in-cell simulations. In the simulations, incoherent synchrotron emission and pair photoproduction in electromagnetic fields are taken into account. If the plasma flows are dense, fast, and hot enough, the overall energy of the synchrotron photons can be much higher than the energy of the generated electromagnetic fields. Furthermore, a sizable number of positrons can be produced due to the pair photoproduction in the generated magnetic field. We propose a rough criterion to judge copious pair production and considerable synchrotron losses. By means of this criterion, we conclude that the incoherent synchrotron emission and the pair production during the Weibel instability can have implications for the collapsar model of gamma-ray bursts.

Incoherent synchrotron emission of laser-driven plasma edge

When a relativistically intense linearly polarized laser pulse is incident on an overdense plasma, a dense electron layer is formed on the plasma edge which relativistic motion results in high harmonic generation, ion acceleration, and incoherent synchrotron emission of gamma-photons. Here we present a self-consistent analytical model that describes the edge motion and apply it to the problem of incoherent synchrotron emission by ultrarelativistic plasma electrons. The model takes into account both coherent radiation reaction from high harmonics and incoherent radiation reaction in the Landau–Lifshitz form. The analytical results are in agreement with 3D particle-in-cell simulations in a certain parameter region that corresponds to the relativistic electronic spring interaction regime.

GYRO-ORBIT SIZE, BRIGHTNESS TEMPERATURE LIMIT, AND IMPLAUSIBILITY OF COHERENT EMISSION BY BUNCHING IN SYNCHROTRON RADIO SOURCES

We show that an upper limit on the maximum brightness temperature for a self-absorbed incoherent synchrotron radio source is obtained from the size of its gyro orbits, which in turn must lie well within the confines of the total source extent. These temperature limits are obtained without recourse to inverse Compton effects or the condition of equipartition of energy between magnetic fields and relativistic particles. For radio variables, the intra-day variability (IDV) implies brightness temperatures $\sim 10^{19}$ K in the co-moving rest frame of the source. This, if interpreted purely due to an incoherent synchrotron emission, would imply gyro radii $>10^{28}$ cm, the size of the universe, while from the causality arguments the inferred maximum size of the source in such a case is $\stackrel{<}{_{\sim}} 10^{15}$ cm. Such high brightness temperatures are sometimes modeled in the literature as some coherent emission process where bunches of non-thermal particles are somehow formed that radiate in phase. We show that, unlike in case of curvature radiation models proposed in pulsars, in the synchrotron radiation mechanism the oppositely charged particles would contribute together to the coherent phenomenon without the need to form separate bunches of the opposite charges. At the same time we show that bunches would disperse over dimensions larger than a wavelength in time shorter than the gyro orbital period ($\stackrel{<}{_{\sim}}0.1$ sec). Therefore a coherent emission by bunches cannot be a plausible explanation of the high brightness temperatures inferred in extragalactic radio sources showing variability over a few hours or longer.

High Observed Brightnesses in Radio Jets

We study the variability properties at radio frequencies of the jets thought to be typical of Active Galactic Nuclei, i.e. bulk Lorentz factor \Gamma ~ 10, and incoherent synchrotron emission. We assume that the radiating electrons are accelerated at shocks within the jet, and that these shocks have a suitable (conical) geometry. In our framework, we can reproduce the variability pattern of Intra Day Variables (20% in less than 1 day) as long as the observed brightness temperature is T_B < 3x10^{17} K. The only stringent condition is an injection timescale of the perturbation shorter than the variability timescale; the geometric condition on the viewing direction is not especially severe, and agrees with the observed occurrence of the phenomenon. For higher values of T_B coherent processes are probably necessary.

A complete sample of GHz-peaked-spectrum radio sources and its radio properties

We define a complete sample of thirty-three GHz-Peaked-Spectrum (GPS) radio sources based on their spectral properties. We present measurements of the radio spectra and polarization of the complete sample and a list of additional GPS sources which fail one or more criteria to be included in the complete sample. The majority of the data have been obtained from quasi-simultaneous multi-frequency observations at the Very Large Array (VLA) during 3 observing sessions. Low frequency data from the Westerbork Synthesis Radio Telescope (WSRT) and from the literature have been combined with the VLA data in order to better define the spectral shape. The objects presented here show a rather wide range of spectral indices at high and low frequencies, including a few cases where the spectral index below the turnover is close to the theoretical value of 2.5 typical of self-absorbed incoherent synchrotron emission. Faint and diffuse extended emission is found in about 10% of the sources. In the majority of the GPS sources, the fractional polarization is found to be very low, consistent with the residual instrumental polarization of 0.3%.

Rapid Variability in S5 0716+714 Across the Electromagnetic Spectrum

We have investigated the rapid variations of the BL Lac object S5 0716+714 in the radio, optical, ultraviolet, and x-ray regimes. Several simultaneous multifrequency campaigns have been carried out. Here we describe the complete analysis of a four-week monitoring campaign at three radio and three optical frequency bands, simultaneous optical-UV and optical-x-ray observations, and the correlations between rapid variations and changes on longer time scales. We also investigate the polarization properties in the radio regime. The major observational results are the high duty cycle of variability in all frequency bands and correlations between the rapid variations in different frequency regimes. The source is almost always variable. Most power resides on time scales of a few days. These rapid variations are closely related over a wide range in frequencies. A close correlation is observed through the optical-radio regime. The simultaneous optical/x-ray investigations are consistent with a close correlation, but the sampling is too poor to determine a transfer function. While no spectral changes have been found in the optical regime, the radio spectral index varies in a similar way as the flux densities do in the radio regime. We find a close correlation with zero lag between the spectral index between 5 and 8.4 GHz, and the optical flux density, indicating that the source gets optically thick in the low-frequency part of the synchrotron branch during states of high optical flux. We interpret the close correlations between the variations in the optical and the radio regime as an indication that the rapid radio variability is not caused by interstellar scintillation. Various arguments rule out gravitational microlensing. Intrinsic intraday radio variability requires enormous brightness temperatures and calls for extremely high boosting factors to avoid the Compton catastrophe, if the radiation is due to incoherent synchrotron emission. We discuss the implications of our observations for various models which aim at explaining rapid variation of nonthermal radiation by either disk or jet models.

Collective emission from rapidly variable quasars

view Abstract Citations (49) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Collective Emission from Rapidly Variable Quasars Benford, Gregory Abstract Recently blazars have shown variability in total flux density, polarization and polarization position angle in both radio and optical bands. This demands brightness temperatures ~10^6^ times the limit set by incoherent synchrotron emission by relativistic electrons. We report laboratory experiments displaying just such enhancement when relativistic beam density exceeds 1% of background plasma density. These suggest a model for collective emission from jets explaining variability and spectral features. It implies that jets could have lower energy electrons in much lower numbers than conventional theory demands, lessening the requirements on the underlying engines. Rapid decay of the high-frequency end of the varying spectra could check these ideas. Publication: The Astrophysical Journal Pub Date: June 1992 DOI: 10.1086/186398 Bibcode: 1992ApJ...391L..59B Keywords: Astronomical Models; Emission Spectra; Quasars; Compton Effect; Computational Astrophysics; Cosmic Plasma; Relativistic Electron Beams; Synchrotron Radiation; Astrophysics; GALAXIES: JETS; GALAXIES: NUCLEI; GALAXIES: QUASARS: GENERAL; RADIO CONTINUUM: GALAXIES full text sources ADS |

An X-ray survey of variable radio bright quasars

A sample consisting primarily of radio bright quasars was observed in X-rays with the Einstein Observatory for times ranging from 1500 to 5000 seconds. Detected sources had luminosities ranging from 0.2 to 41.0 x 10 to the 45th power ergs/sec in the 0.5 to 4.5 keV band. Three of the fourteen objects which were reobserved showed flux increases greater than a factor of two on a time scale greater than six months. No variability was detected during the individual observations. The optical and X-ray luminosities are correlated, which suggests a common origin. However, the relationship (L sub x is approximately L sub op to the (.89 + or - .15) found for historic radio variables may be significantly different than that reported for other radio bright sources. Some of the observed X-ray fluxes were substantially below the predicted self-Compton flux, assuming incoherent synchrotron emission and using VLBI results to constrain the size of the emission region, which suggests relativistic expansion in these sources. Normal CIV emission in two of the sources with an overpredicted Compton component suggests that although they, like BL Lac objects, have highly relativistic material apparently moving at small angle to the line of sight, they have a smaller fraction of the continuum component in the beam.

A metre-wave outburst from the QSO 1055 + 018

Observations of the QSO 1055 + 018 with the Culgoora circular array show that the source flux density doubled at 160 MHz and tripled at 80 MHz during the first seven months of 1983, while complementary observations between 0.843 and 15 GHz revealed no significant changes. Since the 80-MHz quiescent brightness temperature probably exceeds the inverse Compton limit of ∼ 1012 K for incoherent synchrotron emission, the extreme-brightness temperatures deduced from the time variability at metre wave-lengths may naturally be explained by the brightening of a coherent source. Slow interstellar scintillations provide another possible explanation.

Pulsar Optical Emission as Amplified Synchrotron Emission

Pulsed optical emission has been observed from the Crab and Vela pulsars (Manchester and Taylor 1977). The pulse profile of the Crab pulsar has a main pulse and a strong interpulse separated by about 40% of the pulsar period; the peak of the main pulse is just resolved at 20 μs resolution; the spectrum is peaked at about 1014.8 Hz; the pulse profile is constant over long time intervals; both the main pulse and the interpulse are strongly linearly polarized with position angle varying smoothly through each profile and with a minimum of polarization near each peak; the pulses are not significantly circularly polarized. A number of models have been proposed to explain the optical emission from the Crab pulsar but none is completely satisfactory. The spectral peak is too low for incoherent synchrotron emission, the pulse profile is too constant for inverse Compton scattering of radio emission and the similarity with the low-energy X-ray emission argues against coherent curvature emission.

Synchrotron or plasma process emission in narrow-band decimetric type IV bursts

Extremely narrow-banded type IV/subd//subm/ events have been selected to test the various proposed emission mechanisms. Emphasis is put on the observed spectral shape and rapid variations in intensity, and plasma-physical stability of the source model. Synchrotron emission in quasi-vacuum is excluded by the observed steep low-frequency spectral slope. Free-free absorption of incoherent synchrotron emission is negligible compared with the Razin effect suppression. However, Razin-suppressed synchrotron emission would lead to unstably high concentrations of energetic electrons. A low-frequency cutoff due to cyclotron-resonance absorption is unlikely. The coherent synchrotron processes are shown to require either an excessively large number of relativistic electrons or an unstable pitch angle anisotropy. Plasma processes seem to be the necessary explanation for the bursts under consideration. (AIP)