Jean A. Eilek

Reflections of Active Galactic Nucleus Outbursts in the Gaseous Atmosphere of M87

We combined deep Chandra, ROSAT HRI, and XMM-Newton observations of M87 to study the impact of active galactic nucleus (AGN) outbursts on its gaseous atmosphere. Many X-ray features appear to be a direct result of repetitive AGN outbursts. In particular, the X-ray cavities around the jet and counterjet are likely due to the expansion of radio plasma, while rings of enhanced emission at 14 and 17 kpc are probably shock fronts associated with outbursts that began 1-2 × 107 yr ago. The effects of these shocks are also seen in brightenings within the prominent X-ray arms. On larger scales, ~50 kpc from the nucleus, depressions in the surface brightness may be remnants of earlier outbursts. As suggested for the Perseus Cluster by Fabian and his coauthors, our analysis of the energetics of the M87 outbursts argues that shocks may be the most significant channel for AGN energy input into the cooling-flow atmospheres of galaxies, groups, and clusters. For M87, the mean power driving the shock outburst, 2.4 × 1043 ergs s-1, is 3 times greater than the radiative losses from the entire cooling flow. Thus, even in the absence of other energy inputs, outbursts every 3 × 107 yr are sufficient to quench the flow.

Nanosecond radio bursts from strong plasma turbulence in the Crab pulsar

The Crab pulsar was discovered by the occasional exceptionally bright radio pulses it emits, subsequently dubbed ‘giant’ pulses. Only two other pulsars are known to emit giant pulses. There is no satisfactory explanation for the occurrence of giant pulses, nor is there a complete theory of the pulsar emission mechanism in general. Competing models for the radio emission mechanism can be distinguished by the temporal structure of their coherent emission. Here we report the discovery of isolated, highly polarized, two-nanosecond subpulses within the giant radio pulses from the Crab pulsar. The plasma structures responsible for these emissions must be smaller than one metre in size, making them by far the smallest objects ever detected and resolved outside the Solar System, and the brightest transient radio sources in the sky. Only one of the current models—the collapse of plasma-turbulent wave packets in the pulsar magnetosphere—can account for the nanopulses we observe.

Magnetic Fields in Cluster Cores: Faraday Rotation in A400 and A2634

We present Faraday rotation data for radio sources in the centers of the Abell clusters A400 and A2634. These clusters contain large (100 kpc), tailed radio sources, each attached to the central cD galaxy. These clusters do not have strong cooling cores. Our data extend previous work on rotation measure in cluster centers to larger scales and noncooling clusters. The rotation measure, and thus the magnetic field, is ordered on scales ~10-20 kpc in both clusters. The geometry of the rotation measure appears to be determined by the distribution of the X-ray-emitting gas, rather than by the radio tails themselves. We combine our data with previously published X-ray and radio data in order to analyze the magnetic fields in all 12 clusters whose central radio sources have been imaged in rotation measure. We find that the fields are dynamically significant in most clusters. We argue that the Faraday data measure fields in the intracluster medium, rather than in a skin of the radio source. Finally, we consider the nature and maintenance of the magnetic fields in these clusters and conclude that either the cluster-wide field exists at similar levels or a weaker cluster-wide field is amplified by effects in the core.

VLA observations of the multiple jet galaxy 3C 75

VLA observations of the central radio source in Abell 400, 3C 75, at 6 and 20 cm are presented. The VLA maps show that this radio source consists of a pair of twin jets originating in the apparently double nucleus of the central galaxy in this cluster. On larger scales the jets merge into two tails resembling the wide angle tail class of radio sources. Just as for the wide angle tail radio source, 3C 465, it is found that the standard models for bending this source fail quantitatively. The problem becomes even harder because of the low velocity dispersion and temperature for Abell 400 and the fact that the jets from both nuclei bend in the same direction. Models with jet velocities less than 1000 km/s at the first bends seem necessary if the sources are bent by the motion of the galaxy through the ICM. Particle acceleration seems necessary in the most diffuse parts of the source with the energy source likely to be the ICM itself. 10 references.

What bends 3C 465

This paper studies the interaction of the prototypical wide-angle tailed radio source 3C 465 with the ambient cluster gas. 3C 465 is attached to the dominant D galaxy NGC 7720 in the cluster Abell 2634. New VLA maps of the radio source are presented which reveal an inner jet and a rapid change of structure at the hot spots at the beginning of each tail. New X-ray maps of the cluster gas are also presented. It is shown that the sharp bend of the flowing radio-luminous plasma between the inner jets and the beginning of the tails cannot be explained by any of the conventional models. Neither galactic motion, buoyancy, gravitational bending, nor dynamic pressure can account for the bending of this source. Attention is also given to new possibilities for the dynamics of this type of radio tailed source: the effect of a current in the jets, and the interaction with cooling clouds in the cluster gas.

Filaments in the radio lobes of M87

A total intensity VLA image of the inner lobes of M87 at 6 cm is presented. The map has a resolution of 0.4 arcsec and a dynamic range of about 10,000. Several bright features - loops and filaments - are found within the lobes. These features appear to be overpressure compared to the surrounding gas. Several possible origins for these filaments are considered. It is shown that cooling instabilities cannot account for the features. Resistive instabilities are also unlikely unless in situ particle acceleration is occurring. Transonic turbulence or shocks in the lobes might be the most likely explanation of the features. 72 refs.

Flow dynamics and bending of wide-angle tailed radio sources

The dynamics of tailed radio sources (WATs) is studied on the basis of VLA observations of 11 wide-angle WATs at 6 and 20 cm. These new images, in conjunction with optical and X-ray data, are used to describe the unifying characteristics of this class. WATs are found in centers of clusters without cooling cores, associated with galaxies of low space velocity. They are large sources, extending at least 50 kpc from the cluster center, and they have radio power close to the Fanaroff-Riley I/II break. The surface brightness and spectral distributions are used to model the flow fields and bending dynamics of the sources. Two limiting models are employed: the adiabatic model, in which no in situ energization takes place, and the kinetic model, in which all of the radio luminosity comes from in situ energization. It is found that the sources cannot be bent by the slow galaxy motion in the kinetic model. The sources can be bent by the ram pressure of a slowly moving central galaxy in the adiabatic model.

Detection of large Faraday rotation in the inner 2 kiloparsecs of M87

Les cartes de polarisation VLA, a 4 frequences comprisent entre 4.635 et 4.935 GHz, de M 87 sont presentees. De grandes mesures de rotation Faraday sont detectees en direction des lobes radio a 2 kpc. La distribution des mesures de rotation est analysee.

The collective emission of electromagnetic waves from astrophysical jets - Luminosity gaps, BL Lacertae objects, and efficient energy transport

A model of the inner portions of astrophysical jets is constructed in which a relativistic electron beam is injected from the central engine into the jet plasma. This beam drives electrostatic plasma wave turbulence, which leads to the collective emission of electromagnetic waves. The emitted waves are beamed in the direction of the jet axis, so that end-on viewing of the jet yields an extremely bright source (BL Lacertae object). The relativistic electron beam may also drive long-wavelength electromagnetic plasma instabilities (firehose and Kelvin-Helmholtz) that jumble the jet magnetic field lines. After a sufficient distance from the core source, these instabilities will cause the beamed emission to point in random directions and the jet emission can then be observed from any direction relative to the jet axis. This combination of effects may lead to the gap turn-on of astrophysical jets. The collective emission model leads to different estimates for energy transport and the interpretation of radio spectra than the conventional incoherent synchrotron theory. 54 references.

Internal structure and dynamics of the kiloparsec-scale jet in M87

Abstract Detailed analysis of HST and VLA observations enables quantitative modeling of the internal structure of the kiloparsec-scale jet in M87. The jet transverse profiles can be modeled by double-Gaussian profiles. The jet structure is dominated by two threads resembling closely a double helix visible until about 20″ distance. It is produced by a combination of the helical mode and of the elliptical mode of Kelvin–Helmholtz instability. The elliptical mode dominates the pre-knot A jet, while the helical mode becomes prominent at larger distances. Modeling the jet structure constrains well the instability pattern speed, β w =0.5 c and jet viewing angle, θ j =40°. The estimated bulk Lorentz factor of the jet is 3.4. The model reproduces the jet structure on scales of up to 50″ (accounting for the jet curvature).