Knots In 3C Research Articles

Advection of accelerated electrons in radio/X-ray knots of AGN jets

ABSTRACT The X-ray emission from the knots of the kiloparsec scale jet of active galactic nuclei (AGN) suggests the high energy emission process is different from the radio/optical counterpart. Interpretation based on the inverse Compton scattering of cosmic microwave photons has been ruled out through Fermi γ-ray observations for low-redshift sources. As an alternate explanation, synchrotron emission from a different electron population is suggested. We propose a model considering the advected electron distribution from the sites of particle acceleration in AGN knots. This advected electron distribution is significantly different from the accelerated electron distribution and satisfies the requirement of the second electron population. The synchrotron emission from the accelerated and the advected electron distribution can successfully reproduce the observed radio-to-X-ray fluxes of the knots of 3C 273. For the chosen combination of the model parameters, the spectrum due to inverse Compton scattering of cosmic microwave photons falls within the Fermi γ-ray upper limits.

Leptonic or Hadronic Emission: The X-Ray Radiation Mechanism of Large-scale Jet Knots in 3C 273

Abstract A comprehensively theoretical analysis of the broadband spectral energy distributions (SEDs) of large-scale jet knots in 3C 273 is presented to reveal their X-ray radiation mechanism. We show that these SEDs cannot be explained with a single-electron population model when the Doppler boosting effect is either considered or not. By adding a more energetic electron (the leptonic model) or proton (the hadronic model) population, the SEDs of all knots are well represented. In the leptonic model, the electron population that contributes the X-ray emission is more energetic than the one responsible for the radio-optical emission by almost two orders of magnitude; the derived equipartition magnetic field strengths (B eq) are ∼0.1 mG. In the hadronic model, protons with energy ∼20 PeV are required to interpret the observed X-rays; the B eq values are several mG, larger than those in the leptonic model. Based on the fact that no resolved substructures are observed in these knots and the fast cooling time of the high-energy electrons does not easily explain the observed X-ray morphologies, we argue that the two distinct electron populations accelerated in these knots are unreasonable and their X-ray emission is attributed to the proton synchrotron radiation accelerated in these knots. In cases where these knots have relativistic motion toward the observer, the super-Eddington issue of the hadronic model can be avoided. Multiwavelength polarimetry and γ-ray observations with high resolution may be helpful to discriminate these models.

A Photo-hadronic Model of the Large-scale Jets of 3C 273 and PKS 1136–135

Abstract X-ray-bright knots of kiloparsec-scale jets of several radio-loud quasars are an actively discussed issue. Among various models for explaining observations of these phenomena, synchrotron radiation from the electron population that differs from radio to IR-emitting electrons, is promising. However, the origin of this electron population has been debated. Recently, we proposed that this electron population is produced by proton–photon collisions (mainly, the Bethe–Heitler process), and we applied this model to PKS 0637–752. We found that this model works if the proton power is an order of magnitude larger than the Eddington power. In this paper we apply this model to the X-ray emission in the knots of 3C 273 and PKS 1136–135. The target photons for electron–positron pair production are supplied by synchrotron radiation at the radio–IR by primary electrons and by the active galactic nucleus (AGN) core, as well as cosmic microwave background (CMB) radiation. The effects of the AGN photons are included for the first time in the hadronic model. Though the observed X-ray flux is obtained with the contribution of the AGN photons, the required proton power turns out to be highly super-Eddington. However, we find that our model works for a nearly Eddington proton power, if the photon density of the AGN is enhanced. This can occur if the AGN photons are more beamed toward the X-ray knots than toward our line of sight and the AGN photon frequency is shifted by the Doppler effect.

Examining the High-energy Radiation Mechanisms of Knots and Hotspots in Active Galactic Nucleus Jets

Abstract We compile the radio–optical–X-ray spectral energy distributions (SEDs) of 65 knots and 29 hotspots in 41 active galactic nucleus jets to examine their high-energy radiation mechanisms. Their SEDs can be fitted with the single-zone leptonic models, except for the hotspot of Pictor A and six knots of 3C 273. The X-ray emission of 1 hotspot and 22 knots is well explained as synchrotron radiation under the equipartition condition; they usually have lower X-ray and radio luminosities than the others, which may be due to a lower beaming factor. An inverse Compton (IC) process is involved for explaining the X-ray emission of the other SEDs. Without considering the equipartition condition, their X-ray emission can be attributed to the synchrotron-self-Compton process, but the derived jet powers (P jet) are not correlated with L k and most of them are larger than L k, with more than three orders of magnitude, where L k is the jet kinetic power estimated with their radio emission. Under the equipartition condition, the X-ray emission is well interpreted with the IC process for the cosmic microwave background photons (IC/CMB). In this scenario, the derived P jet of knots and hotspots are correlated with and comparable to L k. These results suggest that the IC/CMB model may be a promising interpretation of the X-ray emission. In addition, a tentative knot–hotspot sequence in the synchrotron peak-energy–peak-luminosity plane is observed, similar to the blazar sequence, which may be attributed to the different cooling mechanisms of electrons.

The X-ray emission from the knots in 3C 120

3C 120 is a Seyfert galaxy with a well detected X-ray jet. We investigate the X-ray emission of its five jet knots and fit their spectral energy distributions (SEDs) from the radio to the X-ray bands with a single-zone lepton model. We find that the SEDs of knots k7, s2, and s3 can be explained by synchrotron radiation, and the X-rays are the simple extension of the radio-optical emission component, but that of the inner knot k4 requires the IC/CMB model, in which the X-rays are due to the inverse Compton scattering of the cosmic microwave background photons by relativistic electrons in the jet with a beaming factor δ∼14. The outer knot k25 is resolved into a three-part sub-structure. It is shown that the fitting of the X-rays from this knot with the IC/CMB model needs an extraordinary beaming factor δ∼15–25 for a jet at the kpc scale. If the X-rays of knot k25 are produced by synchrotron radiation similar to k7, s2, and s3, they may be contributed by a relativistic electron population whose radiations in other wavelengths are not detected.

SIGNATURES OF RELATIVISTIC HELICAL MOTION IN THE ROTATION MEASURES OF ACTIVE GALACTIC NUCLEUS JETS

Polarization has proved an invaluable tool for probing magnetic fields in relativistic jets. Maps of the intrinsic polarization vectors have provided the best evidence to date for uniform, toroidally dominated magnetic fields within jets. More recently, maps of the rotation measure (RM) in jets have for the first time probed the field geometry of the cool, moderately relativistic surrounding material. In most cases, clear signatures of toroidal magnetic field are detected, corresponding to gradients in RM profiles transverse to the jet. However, in many objects these profiles also display marked asymmetries which are difficult to explain in simple helical jet models. Furthermore, in some cases the RM profiles are strongly frequency and/or time dependent. Here we show that these features may be naturally accounted for by including relativistic helical motion in the jet model. In particular, we are able to reproduce bent RM profiles observed in a variety of jets, frequency dependent RM profile morphologies and even the time dependence of the RM profiles of knots in 3C 273. Finally, we predict that some sources may show reversals in their RM profiles at sufficiently high frequencies, depending upon the the ratio of the components of jet sheath velocity transverse and parallel to the jet. Thus, multi-frequency RM maps promise a novel way in which to probe the velocity structure of relativistic outflows.

Shedding New Light on the 3C 273 Jet with theSpitzer Space Telescope

We have performed infrared imaging of the jet of the quasar 3C 273 at wavelengths of 3.6 and 5.8 μm with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. When combined with the radio, optical, and X-ray measurements, the IRAC photometry of the X-ray-bright jet knots clearly shows that the optical emission is dominated by the high-energy emission component of the jet, not by the radio synchrotron component, as had been assumed to date. The high-energy component, represented by a power law from the optical through X-ray, may be due to a second synchrotron component or to inverse Compton scattering of ambient photons. In the former case, we argue that the acceleration of protons exceeding energies of Ep ~ 1016 eV or possibly even to Ep ~ 1019 eV would be taking place in the jet knots of 3C 273, assuming that the acceleration time is proportional to the particle gyroradius. In contrast, the inverse Compton model, into which highly relativistic Doppler beaming has to be incorporated, requires very low energy electrons of Ee ~ 1 MeV in the jet knots. The present polarization data in the radio and optical would favor the former interpretation in the case of the 3C 273 jet. Sensitive and detailed measurements of optical polarization are important in order to establish the radiation mechanism responsible for the high-energy emission. The present study offers new clues as to the controversial origin of the X-ray emission seen in many quasar jets.

Chandradetection of hotspot and knots of 3C 303

We report the detection at X-rays of the radio/optical hotspot and knots of 3C 303 from a short (15 ksec) Chandra exposure in 2001 March. The X-ray morphology is similar to that of the radio/optical emission with peaks in the X-ray emission found at 5.5''(knot B), 9'' (knot C) and 17'' (hotspot) from the core of 3C 303. Despite the limited signal-to-noise ratio of the short Chandra exposure, the X-ray photon spectrum was measured for the hotspot. We construct the spectral energy distribution (SED) and find that the X-ray flux is well below the extrapolation of the radio-to-optical continuum, which we interpret as resulting from the production of X-rays via inverse Compton scattering of both synchrotron photons (SSC) and cosmic microwave background photons (EC/CMB). The magnetic field strength, region size, and the maximum energy of electrons are self-consistently determined for the hotspot to be B ~ 4.3 \mu G, R ~ 6.5x10^{21} cm, and G_max ~ 1.4x10^7. This implies a magnetic field strength a factor of ~30 below the equipartition value; B_eq ~ 150 \mu G. The origin of this large departure from equipartition is still uncertain, but the discrepancy is reduced if the plasma in the hotspot is moving with mildly relativistic speeds. Our observation of 3C 303, as well as recent Chandra detections of large scale jets and hotspots in a number of radio galaxies, confirm that particles are accelerated very efficiently in radio galaxies.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] and VLA Observations of Two Optical Continuum Knots in the Jet of 3C 380

We present Hubble Space Telescope Wide Field Planetary Camera 2 broadband red and linear ramp filter (isolating redshifted [O II] λ3727) observations and subarcsecond-resolution 15, 22, and 43 GHz VLA observations of the radio-loud quasar 3C 380. We confirm the report of de Vries et al. that there is good correspondence between the locations of two optical and radio knots/hot spots in the jet. We show that the optical knots are continuum rather than line emission. The radio-optical spectrum can be fitted either by a normal radio spectrum (α ∼ -0.8) with a break somewhere in the infrared or by a steeper single power law (α ∼ -1) (where Sν ∝ να). We suggest that the two knots are radiating optical synchrotron emission. This would make the knots in 3C 380 the most luminous optical knots/hot spots currently known.

VLA observation of radio/optical knots in 3C 277.3 = Coma A

view Abstract Citations (25) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA observation of radio/optical knots in 3C 277.3 = Coma A Bridle, A. H. ; Fomalont, E. B. ; Palimaka, J. J. ; Willis, A. G. Abstract The radio galaxy 3C 277.3 has been mapped at about 1 arcsec resolution using the VLA at 4885 MHz. Its structure resembles that of the inner 50 arcsec of the radio emission from M87. A bridge or jet linking the unresolved central radio core to the southern lobe contains two bright radio knots. One of these coincides with a blue polarized continuum knot in the envelope of the galaxy. Minimum energy calculations for this knot demand in situ particle deposition there, as in the M87 optical-radio jet. If the flow velocity through the knots is of the same order as the 200-300 km/s peculiar radial velocity of an optical emission-line system detected in their vicinity by Miley et al. (1981), two interpretations are possible. Either the magnetic field in the knots is well below its equipartition value, or in situ particle deposition occurs far from the radio core, and a large mass flux through the knots is needed to supply the observed luminosity of the source. Publication: The Astrophysical Journal Pub Date: September 1981 DOI: 10.1086/159174 Bibcode: 1981ApJ...248..499B Keywords: Galactic Structure; Interstellar Matter; Jet Flow; Radio Galaxies; Radio Sources (Astronomy); Flow Velocity; Polarized Radiation; Radial Velocity; Radiation Distribution; Radio Interferometers; Radio Spectra; Astronomy full text sources ADS | data products NED (1)