Equipartition Conditions Research Articles

New filamentary remnant radio emission and duty cycle constraints in the radio galaxy NGC 6086

Radio galaxies are a subclass of active galactic nuclei (AGN) in which accretion onto the supermassive black hole releases energy into the environment via relativistic jets. The jets are not constantly active throughout the life of the host galaxy and alternate between active and quiescent phases. Remnant radio galaxies are detected during a quiescent phase and define a class of unique sources that can be used to constrain the AGN duty cycle. We present, for the first time, a spatially resolved radio analysis of the radio galaxy associated with the galaxy NGC 6086 down to 144 MHz and constraints on the spectral age of the diffuse emission to investigate the duty cycle and evolution of the source. We used three new low-frequency, high-sensitivity observations; the first was performed with the Low Frequency Array at 144 MHz and the other two with the upgraded Giant Metrewave Radio Telescope at 400 MHz and 675 MHz, respectively. To these, we add two Very Large Array archival observations at higher frequencies (1400 and 4700 MHz). In the new observations in the frequency range 144–675 MHz, we detect a second pair of larger lobes and three regions within the remnant emission with a filamentary morphology. We analysed the spectral index trend in the inner remnant lobes and see systematically steeper values (αlow∼1.1–1.3) at the lower frequencies compared to the gigahertz frequencies (αhigh∼0.8–0.9). Steeper spectral indices are found in the newly detected outer lobes (up to αouter∼2.1), as expected if they trace a previous phase of activity of the AGN. However, the differences between the spectra of the two outer lobes suggest different dynamical evolutions within the intra-group medium during their expansion and/or different magnetic field values. Using a single-injection radiative model and assuming equipartition conditions, we place constraints on the age of the inner and outer lobes and derive the duty cycle of the source. We estimate that the duration of the two active phases was 45 Myr and 18 Myr and the duration of the two inactive phases was 66 Myr and 33 Myr. This results in a total active time of ton ∼ 39%. The filamentary structures have a steep spectral index (∼1) without any spectral index trend, and only one of them shows a steepening in the spectrum. Their origin is not yet clear, but they may have formed due to the compression of the plasma or due to magnetic field substructures.

A search for intercluster filaments with LOFAR and eROSITA

ABSTRACT Cosmological simulations predict the presence of warm hot thermal gas in the cosmic filaments that connect galaxy clusters. This gas is thought to constitute an important part of the missing baryons in the Universe. In addition to the thermal gas, cosmic filaments could contain a population of relativistic particles and magnetic fields. A detection of magnetic fields in filaments can constrain early magnetogenesis in the cosmos. So far, the resulting diffuse synchrotron emission has only been indirectly detected. We present our search for thermal and non-thermal diffuse emission from intercluster regions of 106 paired galaxy clusters by stacking the 0.6–2.3 keV X-ray and 144 MHz radio data obtained with the eROSITA telescope onboard the Spectrum-Roentgen-Gamma (SRG) observatory and LOw Frequency ARray (LOFAR), respectively. The stacked data do not show the presence of X-ray and radio diffuse emission in the intercluster regions. This could be due to the sensitivity of the data sets and/or the limited number of cluster pairs used in this study. Assuming a constant radio emissivity in the filaments, we find that the mean radio emissivity is not higher than $1.2\times 10^{-44}\, {\rm erg \, s^{-1} \, cm^{-3} \, Hz^{-1}}$. Under equipartition conditions, our upper limit on the mean emissivity translates to an upper limit of $\sim 75\, {\rm nG}$ for the mean magnetic field strength in the filaments, depending on the spectral index and the minimum energy cutoff. We discuss the constraint for the magnetic field strength in the context of the models for the formation of magnetic fields in cosmic filaments.

Time variability of the core-shift effect in the blazar 3C 454.3

Measuring and inferring the key physical parameters of jets in active galactic nuclei (AGN) requires high-resolution very long baseline interferometry (VLBI) observations. Using VLBI to measure a core-shift effect is a common way of obtaining estimates of the jet magnetic field strength, a key parameter for understanding jet physics. The VLBI core is typically identified as the bright feature at the upstream end of the jet, and the position of this feature changes with the observed frequency, rcore ∝ ν−1/kr. Due to the variable nature of AGN, flares can cause variability of the measured core shift. In this work, we investigated the time variability of the core-shift effect in the luminous blazar 3C 454.3. We employed a self-referencing analysis of multi-frequency (5, 8, 15, 22−24, and 43 GHz) Very Long Baseline Array (VLBA) data covering 19 epochs from 2005 to 2010. We found significant core-shift variability ranging from 0.27 to 0.86 milliarcsec between 5 GHz and 43 GHz. These results confirm the core-shift variability phenomenon observed previously. Furthermore, we also found time variability of the core-shift index, kr, which was typically below one, with an average value of 0.85 ± 0.08 and a standard deviation of 0.30. Values of kr below one were found during flaring and quiescent states. Our results indicate that the commonly assumed conical jet shape and equipartition conditions do not always hold simultaneously. Even so, these conditions are typically assumed when deriving magnetic field strengths from core-shift measurements, which can lead to unreliable results if kr significantly deviates from unity. Therefore, it is necessary to verify that kr = 1 actually holds before using core-shift measurements and the equipartition assumption to derive physical conditions in the jets. When kr = 1 epochs are selected in the case of 3C 454.3, the magnetic field estimates are consistent, even though the core shift varies significantly with time. Subsequently, we estimated the magnetic flux in the jet of 3C 454.3 and found that the source is in the magnetically arrested disc state, which agrees with earlier studies. Finally, we found a good correlation of the core position with the core flux density, rcore ∝ Score0.7, which is consistent with increased particle density during the flares.

Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program

Abstract We analyze the parsec-scale jet kinematics from 2007 June to 2013 January of a sample of γ-ray bright blazars monitored roughly monthly with the Very Long Baseline Array at 43 GHz. In a total of 1929 images, we measure apparent speeds of 252 emission knots in 21 quasars, 12 BL Lacertae objects (BLLacs), and 3 radio galaxies, ranging from 0.02c to 78c; 21% of the knots are quasi-stationary. Approximately one-third of the moving knots execute non-ballistic motions, with the quasars exhibiting acceleration along the jet within 5 pc (projected) of the core, and knots in BLLacs tending to decelerate near the core. Using the apparent speeds of the components and the timescales of variability from their light curves, we derive the physical parameters of 120 superluminal knots, including variability Doppler factors, Lorentz factors, and viewing angles. We estimate the half-opening angle of each jet based on the projected opening angle and scatter of intrinsic viewing angles of knots. We determine characteristic values of the physical parameters for each jet and active galactic nucleus class based on the range of values obtained for individual features. We calculate the intrinsic brightness temperatures of the cores, , at all epochs, finding that the radio galaxies usually maintain equipartition conditions in the cores, while ∼30% of measurements in the quasars and BLLacs deviate from equipartition values by a factor >10. This probably occurs during transient events connected with active states. In the Appendix, we briefly describe the behavior of each blazar during the period analyzed.

On the magnetization of BL Lac jets

The current paradigm foresees that relativistic jets are launched as magnetically dominated flows, whose magnetic power is progressively converted to kinetic power of of the matter of the jet, until equipartition is reached. Therefore, at the end of the acceleration phase, the jet should still carry a substantial fraction ($\approx$ half) of its power in the form of a Poynting flux. It has been also argued that, in these conditions, the best candidate particle acceleration mechanism is efficient reconnection of magnetic field lines, for which it is predicted that magnetic field and accelerated relativistic electron energy densities are in equipartition.Through the modeling of the jet non--thermal emission, we explore if equipartition is indeed possible in BL Lac objects, i.e. low-power blazars with weak or absent broad emission lines. We find that one-zone models (for which only one region is involved in the production of the radiation we observe) the particle energy density is largely dominating (by 1-2 orders of magnitude) over the magnetic one. As a consequence, the jet kinetic power largely exceeds the magnetic power. Instead, if the jet is structured (i.e. made by a fast spine surrounded by a slower layer), the amplification of the IC emission due to the radiative interplay between the two components allows us to reproduce the emission in equipartition conditions.

A Tangential Tracing Control Algorithm for NC Glass Cutter Machine

To ensure the scribe-wheel is always forward along the tangent direction of the cutting path, a new planning algorithm is proposed for the cutter shaft rotating control. The short linear segments used for approximating the cutting curve are separated by the equipartition conditions. For the satisfied ones, the angle between the adjacent segments is linearly interpolated and the cutter shaft rotates without stopping the machine. Otherwise, it needs to stop and rotate the shaft. The experiments show that the deviation error of scribe-wheel is small, and the error existing period is short, which proves the algorithm can achieve the scribe-wheel tangential tracing and satisfy the accuracy requirements while cutting complex shapes.

Insights into the energy equipartition principle in large undamped structures

The question of energy sharing among complex engineering vibrating systems is still an open problem. On the basis of some recent investigations, this paper is addressed to the prediction of the equilibrium energies of interacting conservative resonators and to a better understanding of the principle of energy equipartition for large undamped systems. The analysis explores the field of linear and nonlinear vibrations, the effects of inhomogeneity, the weak or the strong coupling as well as the effect of the initial energy distribution among the subsystems. The principle of energy equipartition is shown to react in a different fashion to these factors. Some general arguments, supported by the results of numerical experiments, enlightening promoting or inhibiting factors to the reaching of energy equipartition conditions, are given.

A multifrequency study of giant radio sources - III. Dynamical age versus spectral age of the lobes of selected sources

The dynamical ages of the opposite lobes of selected giant radio sources are estimated using the DYNAGE algorithm of Machalski et al., and compared with their spectral ages estimated and studied by Jamrozy et al. in Paper II. As expected, the DYNAGE fits give slightly different dynamical ages and other model parameters for the opposite lobes modelled independently of each other, e.g. the age ratios are found to be between ∼1.1 and ∼1.4. Demanding similar values of the jet power and the radio core density for the same source, we look for a self-consistent solution for the opposite lobes, which results in different density profiles along them. We also show that a departure from the equipartition conditions assumed in the model, justified by X-ray observations of the lobes of some nearby radio galaxies, and a relevant variation of the magnetic field strengths may provide an equalization of the ages of the lobes. A comparison of the dynamical and spectral ages shows that a ratio of the dynamical age to the spectral age of the lobes of investigated giant radio galaxies is between ∼1 and ∼5, i.e. similar to that found for smaller radio galaxies. To supplement possible causes for this effect already discussed in the literature, such as uncertainty of the assumed parameters of the model, or influence of a possible departure from the energy equipartition assumption, a further two causes are identified and discussed: (i) a difference between the injection spectral indices describing the initial energy distributions of the emitting relativistic particles determined using the DYNAGE algorithm in the dynamical analysis and in the classical spectral-ageing analysis, and (ii) a different influence of the axial ratio of the lobes in the estimation of the dynamical age and the spectral (synchrotron) age. Arguments are given to suggest that DYNAGE can better take account of radiative effects at lower frequencies than the spectral-ageing analysis. The DYNAGE algorithm is especially effective for sources at high redshifts, for which an intrinsic spectral curvature is shifted to low frequencies.

Are young radio sources in equipartition?

Aims. The knowledge of physical conditions in young radio sources is important for defining the framework of models describing radio source evolution. We investigate whether young radio sources are in equipartition (i.e. minimum energy) conditions by comparing the equipartition magnetic fields of 5 High Frequency Peakers (HFP) with values directly inferred from the spectral peak assumed to be produced by synchrotron self absorption. Methods. Multi-frequency VLBA observations of 5 HFPs were carried out in both the optically thick and thin part of the spectrum to determine the spectral shape and angular size of the components for which individual radio spectra were obtained. Results. We find that the magnetic fields measured using observations agree well with those obtained by assuming equipartition, which implies that these sources are in minimum energy condition and the turnover in their spectra is due probably to SSA. In two source components, we found that the peak of the spectrum is caused by absorption of a thermal plasma instead of being due to SSA. The magnetic fields found in the various components range from 10 to 100 mG. In the presence of such high magnetic fields, electron populations with rather low γ emit in the GHz-regime. In one source, we detect low-surface brightness extended emission at low frequency located ∼30 mas (∼50 pc) from the main source. This feature may be related to either an earlier episode of radio activity or a discontinuous start of the radio activity (sputtering). By comparing our data with previous VLBA observations, we estimate the hotspot advance speed to be in the range 0.1–0.7c and kinematic ages of a few hundred years.

Nonlinear cooling of relativistic particles under equipartition conditions

Aims. In powerful cosmic nonthermal radiation sources with dominant magnetic-field self generation, the plasma physical processes generating these magnetic fields by relativistic plasma instabilities are closely related to the processes energising ultra-high energy radiating electrons in these sources. Then the magnetic field strength becomes time-dependent and adjusts itself to the actual kinetic energy density of the radiating electrons. As a consequence, the synchrotron radiation cooling of individual relativistic electrons exhibits a nonlinear behaviour because of the dependence of the magnetic energy density on the actual time-varying kinetic energy density. Methods. The nonlinear kinetic equation for the intrinsic temperoral evolution of relativistic electrons is solved for the case of instantaneous injection of power-law distributed electrons. Results. The properties of the resulting approximate, nonlinear electron density show significant differences compared to the standard linear solution for constant non-equipartition magnetic-field energy density as, for instance, the different time behaviour of the upper and lower cut-offs of the electron distribution. Also the differential electron fluence as a function of electron energy differs from the linear fluence. For large spectral indices s > 2 of the injected power law, the nonlinear fluence exhibits a weaker break at the lower injected electron cut-off γ1 than the linear fluence. For small spectral indices 1 2) injected power laws, the nonlinear synchrotron fluence at low frequencies approaches a power law ∝ν −0.6 , independent of the value of s, which is identical to the synchrotron fluence behaviour from monoenergetically injected relativistic electrons.

Nonlinear radiative cooling of relativistic particles under equipartition conditions

Context. In powerful cosmic nonthermal radiation sources with dominant magnetic-field self generation, the generation of magnetic fields at almost equipartition strength by relativistic plasma instabilities operates as fast as the acceleration or injection of ultra-high energy radiating electrons and hadrons in these sources. Consequently, the magnetic field strength becomes time-dependent and adjusts itself to the actual kinetic energy density of the radiating electrons in these sources. This coupling of the magnetic field and the magnetic field energy density to the kinetic energy of the radiating particles changes both the synchrotron emissivity and the intrinsic temporal evolution of the relativistic particle energy spectrum after injection. Aims. The nonlinear kinetic equation for the intrinsic temperoral evolution of relativistic electrons is solved for the case of instantaneous injection of monoenergetic particles. Methods. Analytical derivations and graphical illustrations. Results. In blazar and gamma-ray burst sources, the nonlinear synchrotron cooling of each particle under equipartition conditions is then orders of magnitude quicker than the linear cooling behaviour in constant magnetic-field strength sources. This dramatic reduction for the intrinsic radiation loss time may be essential for understanding the observed rapid time variation, of the order of days in the case of the non-blazar radio galaxy M 87 and minutes in flaring blazar jets such as PKS 2155-304. Significant differences in the optically-thin, synchrotron spectral distributions at different times and in the synchrotron light curves at different frequencies are predicted.

Lobe advance velocities in the extragalactic compact symmetric object 4C 31.04

We report on the results of a two epoch study of the low power Compact Symmetric Object 4C 31.04. Observations performed with the VLBA at 5 GHz in 1995 and 2000 have yielded images of this source at milliarcsecond angular resolution. A central core is detected, with bright compact hot spots and extended lobes on both sides. Model-fitting and other analys is of the data (brightness profile, di fference map) clearly indicate that the source is expanding. We estimate the velocity of this expansion to be (0.085± 0.016) mas/yr, i.e. (0.33± 0.06) h −1 65 c in both hot spots. Assuming a constant expansion velocity, we estimate the kinematic age of the source at 550 yrs. We also study the spectral index using VLBA observations at 1.3 GHz and MERLIN at 22 GHz. The derived spectral age is 3000-5000 years in equipartition conditions. The two estimates are discuss ed and found to be in agreement, given present uncertainties.

Brightness Temperature Constraints to Compact Synchrotron Source Radiation Obtained from IDV and VLBI Observations

AbstractWe discuss the observational and theoretical constraints on the brightness temperature of compact opaque synchrotron sources. We consider the implication of observed apparent velocities on the amount of Doppler boosting and compare this with values deduced from directly measured brightness temperatures from ground and space based VLBI observations, as well as the implications of intraday variability. We also discuss the maximum rest frame brightness temperature expected under conditions of both inverse Compton cooling and equipartition conditions.

Radio Bridge Structure and Its Application to Estimate the Mach Number and Ambient Gas Temperature of Powerful Sources

Radio Bridge Structure and Its Application to Estimate the Mach Number and Ambient Gas Temperature of Powerful Sources

Extended X-ray emission associated with the northern hotspot of

ROSAT Position Sensitive Proportional Counter (PSPC) observations of the double-lobed radio source 3C 390.3 show resolved X-ray emission spatially located at the position of the northern radio hotspot. Possible origins for this X-ray emission are discussed. It is found that neither thermal emission nor inverse Compton emission could account for the observed X-rays if particle-field equipartition conditions must prevail. Alternatively, the available multifrequency data from the northern hotspot are consistent with a smoothly decaying synchrotron spectrum from the radio to the X-ray frequencies. In such case, the shape of the synchrotron spectrum is similar to those seen in the western hotspots of Pictor A and 3C 303.

The jet in M87

view Abstract Citations (26) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The jet in M 87. Hardee, P. E. Abstract Observations of the M87 jet are used to investigate the nature of the jet. The jet appears to be expanding and twisted into a helix. Equipartition conditions are calculated at the position of the knots along the expanding jet, and the implications of jet helicity are explored. Jet helicity is interpreted as being produced by helical instability of the flow, and the polarization properties of a helical expanding jet are investigated. Jet helicity produced by instability is shown to imply a supersonic Mach 15 jet more dense than the surrounding medium. When this result is combined with the calculated jet conditions it is found that the jet flow velocity is approximately 30,000 km/s and energy flow is about 200 times the jet luminosity. This provides an energy reservoir for particle acceleration and adiabatic expansion of the radio lobe. While the radio lobes would require 5 x 10 to the 6th yr to develop, the jet could achieve its present configuration in less than 2 x 10 to the 5th yr. Publication: The Astrophysical Journal Pub Date: October 1982 DOI: 10.1086/160356 Bibcode: 1982ApJ...261..457H Keywords: Galactic Radio Waves; Galactic Structure; Helical Flow; Plasma Jets; Radio Galaxies; Supersonic Jet Flow; Electron Acceleration; Equipartition Theorem; Flow Stability; Polarization Characteristics; Astrophysics full text sources ADS | data products SIMBAD (2) NED (1)