Power Jets Research Articles

The LOFAR – eFEDS survey: The incidence of radio and X-ray AGN and the disk–jet connection

Context. Radio jets are present in a diverse sample of AGN. However, the mechanisms of jet powering are not fully understood, and it remains unclear to what extent they obey mass-invariant scaling relations similar to those found for the triggering and fuelling of X-ray-selected AGN. Aims. We use the multi-wavelength data in the eFEDS field observed by eROSITA/Spectrum-Roentgen-Gamma (SRG) and LOFAR to study the incidence of X-ray and radio AGN as a function of several stellar mass (M*)-normalised AGN power indicators. Methods. From the LOFAR – eFEDS survey, we defined a new sample of radio AGN, with optical counterparts from Legacy Survey DR9, according to a radio-excess relative to their host star formation rate. We further divided the sample into compact and complex radio morphologies. In this work, we used the subset matching to the well-characterised, highly complete spectroscopic GAMA09 galaxies (0 < z < 0.4). We release this value-added LOFAR – eFEDS catalogue*. We calculated the fraction of GAMA09 galaxies hosting radio, X-ray, and both radio and X-ray AGN as functions of the specific black hole kinetic (λJet) and radiative (λEdd) power. Results. Despite the soft-X-ray eROSITA-selected sample, the incidence of X-ray AGN as a function of λEdd shows the same mass-invariance and power law slope (−0.65) as that found in previous studies once corrected for completeness. Across the M* range probed, the incidence of compact radio AGN as a function of λJet is described by a power law with constant slope, showing that it is not only high mass galaxies hosting high power jets and vice versa. This slope is steeper than that of the X-ray incidence, which has a value of around −1.5. Furthermore, higher-mass galaxies are more likely to host radio AGN across the λJet range, indicating some residual mass dependence of jet powering. Upon adding complex radio morphologies, including 34 FRIIs, three of which are giant radio galaxies, the incidence not only shows a larger mass dependence but also a jet power dependence, being clearly boosted at high λJet values. Importantly, the latter effect cannot be explained by such radio AGN residing in more dense environments (or more massive dark matter haloes). The similarity in the incidence of quiescent and star-forming radio AGN reveals that radio AGN are not only found in “red and dead” galaxies. Overall, our incidence analysis reveals some fundamental statistical properties of radio AGN samples, but highlights open questions regarding the use of a single radio luminosity–jet power conversion. We explore how different mass and accretion rate dependencies of the incidence can explain the observed results for varying disk–jet coupling models.

Pair Plasma Cascade in Rotating Black Hole Magnetospheres with a Split Monopole Flux Model

An electron-positron cascade in the magnetospheres of Kerr black holes (BHs) is a fundamental ingredient to fueling the relativistic γ-ray jets seen at the polar regions of galactic supermassive BHs (SMBHs). This leptonic cascade occurs in the spark gap region of a BH magnetosphere where the unscreened electric field parallel to the magnetic field is present; hence, it is affected by the magnetic field structure. A previous study explored the case of a thin accretion disk, representative of active galactic nuclei. Here we explore the case of a quasi-spherical gas distribution, as is expected to be present around the SMBH Sgr A* in the center of our Milky Way galaxy, for example. The properties and efficiency of the leptonic cascade are studied. The findings of our study and the implications for SMBH systems in various spectral and accretion states are discussed. The relationships and scalings derived from varying the mass of the BH and background photon spectra are further used to analyze the leptonic cascade process to power jets seen in astronomical observations. In particular, one finds the efficiency of the cascade in a quasi-spherical gas distribution peaks at the jet axis. Observationally, this should lead to a more prominent jet core, in contrast to the thin disk accretion case, where it peaks around the jet–disk interface. One also finds the spectrum of the background photons plays a key role. The cascade efficiency is maximum for a spectral index of 2, while harder and softer spectra lead to a less efficient cascade.

Numerical modelling of the lobes of radio galaxies – Paper V: universal pressure profile cluster atmospheres

ABSTRACT We present relativistic magnetohydrodynamic modelling of jets running into hydrostatic, spherically symmetric cluster atmospheres. For the first time in a numerical simulation, we present model cluster atmospheres based upon the universal pressure profile (UPP), incorporating a temperature profile for a ‘typical’ self-similar atmosphere described by only one parameter – M500. We explore a comprehensive range of realistic atmospheres and jet powers and derive dynamic, energetic, and polarimetric data which provide insight into what we should expect of future high-resolution studies of AGN outflows. From the simulated synchrotron emission maps which include Doppler beaming we find sidedness distributions that agree well with observations. We replicated a number of findings from our previous work, such as higher power jets inflating larger aspect-ratio lobes, and the cluster environment impacting the distribution of energy between the lobe and shocked regions. Comparing UPP and β-profiles we find that the cluster model chosen results in a different morphology for the resultant lobes with the UPP more able to clear lobe material from the core; and that these different atmospheres influence the ratio between the various forms of energy in the fully developed lobes. This work also highlights the key role played by Kelvin–Helmholtz instabilities in the formation of realistic lobe aspect ratios. Our simulations point to the need for additional lobe-widening mechanisms at high jet powers, for example jet precession. Given that the UPP is our most representative general cluster atmosphere, these numerical simulations represent the most realistic models yet for spherically symmetric atmospheres.

Stellar-mass black hole spinning and its relation to transient jets

Despite the vast research on spinning black holes and jets, little is known about details of jet formation. This paper is aimed to study whether Penroses prediction that black hole spin power jets can be verified. Once proved, a deeper understanding of energy/momentum transfer near event horizon is to be achieved. This paper compares two dominant spin measuring methods. Thermal continuum fitting method makes use of thermal emission to measure the spin, where a theoretical flux profile is created by inputting parameters (inclination of X-ray binaries, distance of X-ray binaries from the earth, mass of black hole, etc). X-ray reflection method uses broadened Fe-line to measure the spin, and that corona geometry is often required. This paper also compares various definitions of jet power and spin-jets relation. In conclusion, transient jets are highly possible to be powered by black hole spin, but more evidence is required to confirm this. Steady jets remain in a vague relation with spin. It has also been found that different measuring methods of both spin and jets can affect the spin-jets relation.

A Simulation Study of Ultra-relativistic Jets. II. Structures and Dynamics of FR-II Jets

Abstract We study the structures of ultra-relativistic jets injected into the intracluster medium and the associated flow dynamics, such as shocks, velocity shear, and turbulence, through three-dimensional relativistic hydrodynamic (RHD) simulations. To that end, we have developed a high-order accurate RHD code, equipped with a weighted essentially non-oscillatory scheme and a realistic equation of state. Using the code, we explore a set of jet models with the parameters relevant to FR-II radio galaxies. We confirm that the overall jet morphology is primarily determined by the jet power, and the jet-to-background density and pressure ratios play secondary roles. Jets with higher powers propagate faster, resulting in more elongated structures, while those with lower powers produce more extended cocoons. Shear interfaces in the jet are dynamically unstable, and hence, chaotic structures with shocks and turbulence develop. We find that the fraction of the jet-injected energy dissipated through shocks and turbulence is greater in less powerful jets, although the actual amount of the dissipated energy is larger in more powerful jets. In lower power jets, the backflow is dominant in the energy dissipation owing to the broad cocoon filled with shocks and turbulence. In higher power jets, by contrast, both the backflow and jet-spine flow are important for the energy dissipation. Our results imply that different mechanisms, such as diffusive shock acceleration, shear acceleration, and stochastic turbulent acceleration, may be involved in the production of ultra-high energy cosmic rays in FR-II radio galaxies.

AGN jet feedback on a moving mesh: gentle cluster heating by weak shocks and lobe disruption

ABSTRACT While there is overwhelming observational evidence of active galactic nuclei (AGN)-driven jets in galaxy clusters and groups, if and how the jet energy is delivered to the ambient medium remains unanswered. Here, we perform very high-resolution AGN jet simulations within a live, cosmologically evolved cluster with the moving mesh code arepo. We find that mock X-ray and radio lobe properties are in good agreement with observations with different power jets transitioning from FR-I to FR-II-like morphologies. During the lobe inflation phase, heating by both internal and bow shocks contributes to lobe energetics, and ∼40 per cent of the feedback energy goes into the PdV work done by the expanding lobes. Low power jets are more likely to simply displace gas during lobe inflation, but higher power jets become more effective at driving shocks and heating the intracluster medium (ICM), although shocks rarely exceed $\mathcal {M}\sim 2-3$. Once the lobe inflation phase ceases, cluster weather significantly impacts the lobe evolution. Lower power jet lobes are more readily disrupted and mixed with the ICM, depositing up to ∼70 per cent of the injected energy; however, ultimately the equivalent of $\lower.5ex\hbox{$\,\, \buildrel\gt \over \sim \,\,$}50$ per cent of the feedback energy ends up as potential energy of the system. Even though the mean ICM entropy is increased up to 80 Myr after the jets switch off, AGN heating is gentle, inducing no large variations in cluster radial profiles in accord with observations.

Simulating the dynamics and non-thermal emission of relativistic magnetized jets I. Dynamics

ABSTRACT We have performed magnetohydrodynamic (MHD) simulations of relativistic jets from supermassive blackholes over a few tens of kpc for a range of jet parameters. One of the primary aims was to investigate the effect of different MHD instabilities on the jet dynamics and their dependence on the choice of jet parameters. We find that two dominant MHD instabilities affect the dynamics of the jet, small-scale Kelvin–Helmholtz (KH) modes and large-scale kink modes, whose evolution depends on internal jet parameters like the Lorentz factor, the ratio of the density and pressure to the external medium, and the magnetization and hence consequently on the jet power. Low power jets are susceptible to both instabilities, kink modes for jets with higher central magnetic field and KH modes for lower magnetization. Moderate power jets do not show appreciable growth of kink modes, but KH modes develop for lower magnetization. Higher power jets are generally stable to both instabilities. Such instabilities decelerate and decollimate the jet while inducing turbulence in the cocoon, with consequences on the magnetic field structure. We model the dynamics of the jets following a generalized treatment of the Begelman–Cioffi relations, which we present here. We find that the dynamics of stable jets match well with simplified analytic models of expansion of non-self-similar FRII jets, whereas jets with prominent MHD instabilities show a nearly self-similar evolution of the morphology as the energy is more evenly distributed between the jet head and the cocoon.

Mid-infrared variability of γ-ray emitting blazars

ABSTRACT Using data from the Wide-field Infrared Survey Explorer, we studied the mid-infrared (mid-IR) 3.4 μm (W1-band) and 4.6 μm (W2-band) flux variability of γ-ray emitting blazars. Our sample consists of 460 flat spectrum radio quasars (FSRQs) and 575 BL Lacertae (BL Lac) objects. On intraday time-scales, the median amplitude of variability (σm) for FSRQs is 0.04$^{+0.03}_{-0.02}$ and 0.05$^{+0.03}_{-0.02}$ mag in W1 and W2 bands. For BL Lacs, we found median σm in W1(W2) bands of 0.04$^{+0.01}_{-0.02}$ (0.04$^{+0.02}_{-0.02}$) mag. On long time-scales, for FSRQs we found a median σm of 0.44$^{+0.28}_{-0.27}$ and 0.45$^{+0.27}_{-0.27}$ mag in W1 and W2 bands, while for BL Lacs, the median values are 0.21$^{+0.18}_{-0.12}$ and 0.22$^{+0.18}_{-0.11}$ mag in W1 and W2 bands. From statistical tests, we found FSRQs to show larger σm than BL Lacs on both intraday and long time-scales. Among blazars, low synchrotron peaked sources showed larger σm compared to intermediate synchrotron peaked and high synchrotron peaked sources. The larger σm seen in FSRQs relative to BL Lacs on both intraday and long time-scales could be due to them having the most powerful relativistic jets and/or their mid-IR band coinciding with the peak of the electron energy distribution. BL Lacs have low power jets and the observational window too traces the emission from low-energy electrons, thereby leading to low σm. In both FSRQs and BL Lacs predominantly a bluer when brighter behaviour was observed. No correlation is found between σm and black hole mass.

General Physical Properties of Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies

Abstract We present the results of a detailed multiwavelength study of a sample of 16 narrow-line Seyfert 1 (NLSy1) galaxies known in γ-rays so far. This includes a focused X-ray spectral analysis, to compare them with a more general NLSy1 population, and a broadband spectral energy distribution (SED) modeling considering the leptonic radiative processes to understand their similarity/dissimilarity with blazars. The X-ray spectra of γ-NLSy1 galaxies exhibit similarities to both typical NLSy1 sources below ≲2 keV and blazars at higher energies. We also find weak evidences of excess absorption in the soft X-ray spectra of three sources and a tentative detection of the Fe line in 1H 0323+342. A comparison of the broadband parameters derived from the SED modeling reveals the similarity of γ-NLSy1 objects to blazars, in particular to flat-spectrum radio quasars. The γ-NLS1 galaxies host relatively low power jets with small bulk Lorentz factors with respect to blazars, and this explains the paucity of such sources in the γ-ray catalogs and identification of even fewer parent population members. Many of the observed features of these intriguing objects suggest that they host low-mass black holes. The accretion rate in Eddington units can be considered as the driving factor to explain the physical properties of γ-NLSy1 sources, similar to that which is known for the general blazar population.

Harnessing the QCD power spectrum for high energy physics

We introduce a new framework to encode information in the QCD power spectrum on an event-by-event basis from which jets and their substructure can be extracted. Our new “power jets” scheme requires no jet radius parameter, and allows pileup to be extracted in situ. The result is an accurate kinematic reconstruction of underlying hard physics which is robust to extremely high pileup.

Disc–jet coupling in low-luminosity accreting neutron stars

In outburst, neutron star X-ray binaries produce less powerful jets than black holes at a given X-ray luminosity. This has made them more difficult to study as they fade towards quiescence. To explore whether neutron stars power jets at low accretion rates ($L_{\rm X} \lesssim 10^{36}$ erg s$^{-1}$), we investigate the radio and X-ray properties of three accreting millisecond X-ray pulsars (IGR J17511-3057, SAX J1808.4-3658 and IGR J00291+5934) during their outbursts in 2015, and of the non-pulsing neutron star Cen X-4 in quiescence (2015) and in outburst (1979). We did not detect the radio counterpart of IGR J17511-3057 in outburst or of Cen X-4 in quiescence, but did detect IGR J00291+5934 and SAX J1808.4-3658, showing that at least some neutron stars launch jets at low accretion rates. While the radio and X-ray emission in IGR J00291+5934 seem to be tightly correlated, the relationship in SAX J1808.4-3658 is more complicated. We find that SAX J1808.4-3658 produces jets during the reflaring tail, and we explore a toy model to ascertain whether the radio emission could be attributed to the onset of a strong propeller. The lack of a universal radio/X-ray correlation, with different behaviours in different neutron star systems (with various radio/X-ray correlations; some being radio faint and others not), points at distinct disk-jet interactions in individual sources, while always being fainter in the radio band than black holes at the same X-ray luminosity.

Relativistic jet feedback in high-redshift galaxies – I. Dynamics

We present the results of three dimensional relativistic hydrodynamic simulations of interaction of AGN jets with a dense turbulent two-phase interstellar medium, which would be typical of high redshift galaxies. We describe the effect of the jet on the evolution of the density of the turbulent ISM. The jet driven energy bubble affects the gas to distances up to several kiloparsecs from the injection region. The shocks resulting from such interactions create a multi-phase ISM and radial outflows. One of the striking result of this work is that low power jets (P_jet < 10^{43} erg/s) although less efficient in accelerating clouds, are trapped in the ISM for a longer time and hence affect the ISM over a larger volume. Jets of higher power drill through with relative ease. Although the relativistic jets launch strong outflows, there is little net mass ejection to very large distances, supporting a galactic fountain scenario for local feedback.

Black hole Meissner effect and Blandford-Znajek jets

Spinning black holes tend to expel magnetic fields. In this way they are similar to superconductors. It has been a persistent concern that this black hole ``Meissner effect'' could quench jet power at high spins. This would make it impossible for the rapidly rotating black holes in Cyg X-1 and GRS $1915+105$ to drive Blandford-Znajek jets. We give a simple geometrical argument why fields which become entirely radial near the horizon are not expelled by the Meissner effect and may continue to power jets up to the extremal limit. A simple and natural example is a split-monopole field. We stress that ordinary Blandford-Znajek jets are impossible if the Meissner effect operates and expels the field. Finally, we note that in our general relativistic magnetohydrodynamic simulations of black hole jets, there is no evidence that jets are quenched by the Meissner effect. The simulated jets develop a large split-monopole component spontaneously which supports our proposal for how the Meissner effect is evaded and jets from rapidly rotating black holes are powered in nature.

COLLECTIVE EVIDENCE FOR INVERSE COMPTON EMISSION FROM EXTERNAL PHOTONS IN HIGH-POWER BLAZARS

We present the first collective evidence that Fermi-detected jets of high kinetic power (L_kin) are dominated by inverse Compton emission from upscattered external photons. Using a sample with a broad range in orientation angle, including radio galaxies and blazars, we find that very high power sources (L_kin > 10^45.5 erg s^{-1}) show a significant increase in the ratio of inverse Compton to synchrotron power (Compton dominance) with decreasing orientation angle, as measured by the radio core dominance and confirmed by the distribution of superluminal speeds. This increase is consistent with beaming expectations for external Compton (EC) emission, but not for synchrotron self Compton (SSC) emission. For the lowest power jets (L_kin < 10^43.5 erg s^{-1}), no trend between Compton and radio core dominance is found, consistent with SSC. Importantly, the EC trend is not seen for moderately high power flat spectrum radio quasars with strong external photon fields. Coupled with the evidence that jet power is linked to the jet speed (Kharb et al. 2010), this finding suggests that external photon fields become the dominant source of seed photons in the jet comoving frame only for the faster and therefore more powerful jets.

DISK-OUTFLOW COUPLING: ENERGETICS AROUND SPINNING BLACK HOLES

The mechanism by which outflows and plausible jets are driven from black hole systems, still remains observationally elusive. Notwithstanding, several observational evidences and deeper theoretical insights reveal that accretion and outflow/jet are strongly correlated. We model an advective disk-outflow coupled dynamics, incorporating explicitly the vertical flux. Inter-connecting dynamics of outflow and accretion essentially upholds the conservation laws. We investigate the properties of the disk-outflow surface and its strong dependence on the rotation parameter of the black hole. The energetics of the disk-outflow strongly depend on the mass, accretion rate and spin of the black holes. The model clearly shows that the outflow power extracted from the disk increases strongly with the spin of the black hole, inferring that the power of the observed astrophysical jets has a proportional correspondence with the spin of the central object. In case of blazars (BL Lacs and Flat Spectrum Radio Quasars), most of their emission are believed to be originated from their jets. It is observed that BL Lacs are relatively low luminous than Flat Spectrum Radio Quasars (FSRQs). The luminosity might be linked to the power of the jet, which in turn reflects that the nuclear regions of the BL Lac objects have a relatively low spinning black hole compared to that in the case of FSRQ. If the extreme gravity is the source to power strong outflows and jets, then the spin of the black hole, perhaps, might be the fundamental parameter to account for the observed astrophysical processes in an accretion powered system.

On the aerodynamics of the Miles M.52 (E.24/43) – a historical perspective

AbstractThe aerodynamic design of the Miles M.52 experimental supersonic aircraft is reviewed relative to the state of knowledge at its time of 1943 – 1946. Drawing on widely-ranging material, much not previously published, this study enlarges upon, and in places amends, previous accounts of the project.Based on advice collated from the fields of aerodynamics and ballistics, Miles conceived an original and forward-looking design, backed by an extensive test programme. Novel solutions to new requirements in the areas of structures and systems provided a robust airframe, showing fair prospects of being stable and controllable throughout the specified flight envelope. An equally innovative power plant was devised for it by Whittle’s company, Power Jets Ltd.Contradictory predictions of its performance were made by Miles and the RAE, through differences in their estimations of fuselage drag. A new evaluation suggests that the available information would have shown the aircraft to be capable of providing vital aerodynamic data for the transonic and early supersonic regimes at a time when no other sources were available, though further engine development would be needed for it to reach its full potential.

Coal as a low-carbon fuel?

The conversion of coal into liquid fuel is one of the dirtiest ways to produce transportation fuel. But if carbon is captured and stored, and some biomass is added, it could become the cleanest way to power jets, trucks and trains.

Jets from young stars

Most stars produce spectacular jets during their formation. There are thousands of young stars within 500 pc of the Sun and many power jets. Thus, protostellar jets may be the most common type of collimated astrophysical outflow. Shocks powered by outflows excite emission lines throughout the spectrum, exhibit a rich variety of structure, and motions with velocities ranging from less than 20 to over 500 km s−1. Due to their relative proximity, proper motions and structural changes can be observed in less than a year. I review the properties of classical Herbig-Haro objects, irradiated jets, and outflows emerging from the nearest massive star forming regions. Protostellar outflows are ideal laboratories for the exploration of the jet physics.

Low power compact radio galaxies at high angular resolution

We present sub-arcsecond resolution multi-frequency (8 and 22 GHz) VLA images of five low power compact (LPC) radio sources, and phase referenced VLBA images at 1.6 GHz of their nuclear regions. At the VLA resolution we resolve the structure and identify component positions and flux densities. The phase referenced VLBA data at 1.6 GHz reve als flat-spectrum, compact cores (down to a few milliJansky) in f our of the five sources. The absolute astrometry provided by t he phase referencing allows us to identify the center of activi ty on the VLA images. Moreover, these data reveal rich structures, including two-sided jets and secondary components. On the basis of the arcsecond scale structures and of the nuclear properties, we rule out the presence of strong relativistic effects in our LPCs, which must be intrinsically small (deprojected linear sizes < 10 kpc). Fits of continuous injection models reveal break frequencies in the GHz domain, and ages in the range 10 5 − 10 7 yrs. In LPCs, the outermost edge may be advancing more slowly than in more powerful sources or could even be stationary; some LPCs might also have ceased their activity. In general, the properties of LPCs can be related to a number of reasons, including, but not limited to: youth, frustration, low kinematic power jets, and short-lived activity in the radio.

The Development of the Whittle Turbojet

Sir Frank Whittle passed away on August 8, 1996, at the age of 89, in Maryland. His work in developing the turbojet can truly be said to represent one of the greatest mechanical engineering achievements in the last 70 years. The development of the turbojet demanded that Whittle face almost insurmountable technical and institutional challenges. The technical challenges included developing centrifugal compressor pressure ratios of 4:1 from the prevailing technology level of 2.5:1, increasing compressor efficiencies from 65 to 80 percent while designing for combustion intensities that were 10 times the prevailing state of the art in boiler technology. He was also responsible for utilizing a vortex turbine design approach. The institutional challenges that he faced included changing a paradigm on aircraft propulsion technology and nurturing Power Jets Ltd. to produce excellent engine designs with minimal resources in terms of money, technical manpower, and governmental support. It is the object of this paper to document the epic long-drawn-out struggle fought by Sir Frank against entrenched technical opinion, which ultimately resulted in the turbojet revolution. The technical aspects of his pioneering work with emphasis on the problems he encountered will also be discussed.