Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec-Scale Accelerations

There is growing evidence that relativistic jets in active galactic nuclei undergo extended (parsec-scale) acceleration. We argue that, contrary to some suggestions in the literature, this acceleration cannot be purely hydrodynamic. Using exact semianalytic solutions of the relativistic MHD equations, we demonstrate that the parsec-scale acceleration to relativistic speeds inferred in sources like the radio galaxy NGC 6251 and the quasar 3C 345 can be attributed to magnetic driving. Additional observational implications of this model will be explored in future papers in this series.Comment: 6 pages, 2 figures, submitted to Ap

Temperature and concentration control of exothermic chemical processes in continuous stirred tank reactors

Exothermic chemical reaction taking place in continuous stirred tank reactor is considered. Heat release from the chemical reaction, non-linear dynamic behavior of the process and uncertainty in parameters are the main factors motivating the use of robust control design. Viewing temperature and molar concentration as variables both accessible in real time, PI and optimal state-feedback controllers driven by temperature and concentration error signals are proposed to regulate the system over reactor’s steady-state working points by counteracting undesired disturbances. Since access to concentration value has proved beneficial for the reactor’s performance, estimation techniques are examined to compensate for the problematic nature of the concentration’s measurement. A linear reduced-order observer is first proposed to estimate the concentration value using temperature measurements. In addition, assuming concentration measurement is available with a relatively short delay via sample analysis, a linear and non-linear discrete-time predictor is constructed to estimate the concentration’s real-time value. A linear combination of the two estimation schemes (observer, predictor) is proposed resulting in a combined estimator, in which the emphasis between the two individual schemes can be controlled via a scalar parameter. The work presented in this paper was supported by the GLOW project – New weather-stable low gloss powder coatings based on bifunctional acrylic solid resins and nanoadditives – as part of the development of novel and efficient processing technologies regarding the production of new families of powder coatings, responding to industrial requirements for quality improvement at lower cost and shorter development cycles

Monitoring the Bi-Directional Relativistic Jets of the Radio Galaxy 1946+708

We report on a multi-frequency, multi-epoch campaign of Very Long Baseline Interferometry observations of the radio galaxy 1946+708 using the VLBA and a Global VLBI array. From these high-resolution observations we deduce the kinematic age of the radio source to be $\sim$4000 years, comparable with the ages of other Compact Symmetric Objects (CSOs). Ejections of pairs of jet components appears to take place on time scales of 10 years and these components in the jet travel outward at intrinsic velocities between 0.6 and 0.9 c. From the constraint that jet components cannot have intrinsic velocities faster than light, we derive H_0 > 57 km s^-1 Mpc^-1 from the fastest pair of components launched from the core. We provide strong evidence for the ejection of a new pair of components in ~1997. From the trajectories of the jet components we deduce that the jet is most likely to be helically confined, rather than purely ballistic in nature.Comment: 20 pages, 8 figures, accepted to Ap

Dust Production and Particle Acceleration in Supernova 1987A Revealed with ALMA

Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450um, 870um, 1.4mm, and 2.8mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2Msun). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated to the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.Comment: ApJL accepte

Dissipationless Disk Accretion

We consider disk accretion resulting purely from the loss of angular momentum due to the outflow of plasma from a magnetized disk. In this limiting case, the dissipation due to the viscosity and finite electrical conductivity of the plasma can be neglected. We have obtained self-consistent, self-similar solutions for dissipationless disk accretion. Such accretion may result in the formation of objects whose bolometric luminosities are lower than the flux of kinetic energy in the ejected material.Comment: 17 pages, 6 figures, published in Astronomy Reports, Vol.49, No.1, 2005, p.57 (submitted September 13, 2003). Unfortunately, we did not upload the paper to astro-ph before, but since the topic is now of interest we feel that the paper would benefit the communit

Faraday rotation in the MOJAVE blazars: 3C 273 a case study

Radio polarimetric observations of Active Galactic Nuclei can reveal the magnetic field structure in the parsec-scale jets of these sources. We have observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with the Very Long Baseline Array to study Faraday rotation in a large sample of jets. Our observations re-confirm the transverse rotation measure gradient in 3C 273. For the first time the gradient is seen to cross zero which is further indication for a helical magnetic field and spine-sheath structure in the jet. We believe the difference to previous epochs is due to a different part of the jet being illuminated in our observations.Comment: 6 pages, 3 figures. To appear in the proceedings of "Beamed and Unbeamed Gamma-rays from Galaxies", held in Muonio, Finland, April 11-15, 2011. Journal of Physics: Conference Serie

Atacama compact array observations of the pulsar-wind nebula of SNR 0540-69.3

We present observations of the pulsar-wind nebula (PWN) region of SNR 0540-69.3. The observations were made with the Atacama Compact Array (ACA) in Bands 4 and 6. We also add radio observations from the Australia Compact Array at 3 cm. For 1.449–233.50 GHz, we obtain a synchrotron spectrum Fν∝ν−αν⁠, with the spectral index αν = 0.17 ± 0.02. To conclude how this joins the synchrotron spectrum at higher frequencies, we include hitherto unpublished AKARI mid-infrared data, and evaluate published data in the ultraviolet (UV), optical, and infrared (IR). In particular, some broad-band filter data in the optical must be discarded from our analysis due to contamination by spectral line emission. For the UV/IR part of the synchrotron spectrum, we arrive at αν=0.87+0.08−0.10⁠. There is room for 2.5 × 10−3 M⊙ of dust with a temperature of ∼55 K if there are dual breaks in the synchrotron spectrum, one around ∼9 × 1010 Hz and another at ∼2 × 1013 Hz. The spectral index then changes at ∼9 × 1010 Hz from αν = 0.14 ± 0.07 in the radio to αν=0.35−0.07+0.05 in the millimetre-to-far-IR range. The ACA Band 6 data marginally resolve the PWN. In particular, the strong emission ∼1.′′5 south-west of the pulsar, seen at other wavelengths, and resolved in the 3 cm data with its 0.″8 spatial resolution, is also strong in the millimetre range. The ACA data clearly reveal the supernova remnant shell ∼20–35 arcsec west of the pulsar, and for the shell we derive αν = 0.64 ± 0.05 for the range 8.6–145 GHz

A relativistic model of the radio jets in NGC 315

We apply our intrinsically symmetrical, decelerating relativistic jet model to deep VLA imaging of the inner 140 arcsec of the giant low-luminosity radio galaxy NGC 315. An optimized model accurately fits the data in both total intensity and linear polarization. We infer that the velocity, emissivity and field structure in NGC 315 are very similar to those of the other low-luminosity sources we have modelled, but that all of the physical scales are larger by a factor of about 5. We derive an inclination to the line of sight of 38 degrees for the jets. Where they first brighten, their on-axis velocity is approximately v/c = 0.9. They decelerate to v/c = 0.4 between 8 and 18 kpc from the nucleus and the velocity thereafter remains constant. The speed at the edge of the jet is roughly 0.6 of the on-axis value where it is best constrained, but the transverse velocity profile may deviate systematically from the Gaussian form we assume. The proper emissivity profile is split into three power-law regions separated by shorter transition zones. In the first of these, at 3 kpc (the flaring point) the jets expand rapidly at constant emissivity, leading to a large increase in the observed brightness on the approaching side. At 10 kpc, the emissivity drops abruptly by a factor of 2. Where the jets are well resolved their rest-frame emission is centre-brightened. The magnetic field is modelled as random on small scales but anisotropic and we rule out a globally ordered helical configuration. To a first approximation, the field evolves from a mixture of longitudinal and toroidal components to predominantly toroidal, but it also shows variations in structure along and across the jets, with a significant radial component in places. Simple adiabatic models fail to fit the emissivity variations.Comment: 20 pages, 17 figures, MNRAS (in press

Relativistic Magnetohydrodynamics with Application to Gamma-Ray Burst Outflows: I. Theory and Semianalytic Trans-Alfvenic Solutions

We present a general formulation of special-relativistic magnetohydrodynamics and derive exact radially self-similar solutions for axisymmetric outflows from strongly magnetized, rotating compact objects. We generalize previous work by including thermal effects and analyze in detail the various forces that guide, accelerate, and collimate the flow. We demonstrate that, under the assumptions of a quasi-steady poloidal magnetic field and of a highly relativistic poloidal velocity, the equations become effectively time-independent and the motion can be described as a frozen pulse. We concentrate on trans-Alfvenic solutions and consider outflows that are super-Alfvenic throughout in the companion paper. Our results are applicable to relativistic jets in gamma-ray burst (GRB) sources, active galactic nuclei, and microquasars, but our discussion focuses on GRBs. We envision the outflows in this case to initially consist of a hot and optically thick mixture of baryons, electron-positron pairs, and photons. We show that the flow is at first accelerated thermally but that the bulk of the acceleration is magnetic, with the asymptotic Lorentz factor corresponding to a rough equipartition between the Poynting and kinetic-energy fluxes (i.e., \~50% of the injected total energy is converted into baryonic kinetic energy). The electromagnetic forces also strongly collimate the flow, giving rise to an asymptotically cylindrical structure.Comment: 22 pages, 5 figures, submitted to the Astrophysical Journal. The companion paper is astro-ph/030348