Features of Structure and Absorption in the Jet-Launching Region of M87

M87 is one of the best available source for studying the AGN jet-launching region. To enrich our knowledge of this region, with quasi-simultaneous observations using VLBA at 22, 43 and 86 GHz, we capture the images of the radio jet in M87 on a scale within several thousand R s . Based on the images, we analyze the transverse jet structure and obtain the most accurate spectral-index maps of the jet in M87 so far, then for the first time, we compare the results of the two analyses and find a spatial association between the jet collimations and the local enhancement of the density of external medium in the jet-launching region. We also find the external medium is not uniform, and greatly contributes to the free-free absorption in this region. In addition, we find for the jet in M87, its temporal morphology in the launching region may be largely affected by the local, short-lived kink instability growing in itself.

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Radio polarization observations of large supernova remnants at λ6 cm

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313009472 ◽

2013 ◽

Vol 9 (S296) ◽

pp. 202-209 ◽

Cited By ~ 1

Author(s):

J. L. Han ◽

X. Y. Gao ◽

X. H. Sun ◽

W. Reich ◽

L. Xiao ◽

...

Keyword(s):

Magnetic Field ◽

Spectral Index ◽

Supernova Remnants ◽

Galactic Plane ◽

Measured Flux ◽

Thermal Spectrum ◽

Intrinsic Magnetic Field ◽

Spectral Break ◽

Index Maps ◽

First Time

AbstractWe have observed 79 supernova remnants (SNRs) with the Urumqi 25 m telescope at λ6 cm during the Sino-German λ6 cm polarization survey of the Galactic plane. We measured flux densities of SNRs at λ6 cm, some of which are the first ever measured or the measurements at the highest frequency, so that we can determine or improve spectra of SNRs. Our observations have ruled out spectral breaks or spectral flattening that were suggested for a few SNRs, and confirmed the spectral break of S147. By combining our λ6 cm maps with λ11 cm and λ21 cm maps from the Effelsberg 100 m telescope, we calculated the spectral index maps of several large SNRs. For many remnants we obtained for the first time polarization images, which show the intrinsic magnetic field structures at λ6 cm. We disapproved three objects as being SNRs, OA184, G192.8−1.1 and G16.8−1.1, which show a thermal spectrum and no polarization. We have discovered two large supernova remnants, G178.2−4.2 and G25.1−2.3., in the survey maps.

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Space VLBI Observations of PKS 1921-293

Symposium - International Astronomical Union ◽

10.1017/s0074180900220706 ◽

2001 ◽

Vol 205 ◽

pp. 128-129

Author(s):

Zhi-Qiang Shen ◽

Philip G. Edwards ◽

Seiji Kameno ◽

Makoto Inoue ◽

James E. J. Lovell

Keyword(s):

Brightness Temperature ◽

Spectral Index ◽

Rest Frame ◽

The Core ◽

Vlbi Observations ◽

First Time

We present results of the first space VLBI observations of PKS 1921-293. An inner jet component about 1.5 mas north of the core is revealed for the first time. The compact core is partially resolved, but still has a brightness temperature (at the source rest frame) of 3.0×1012 K. A spectral index map made by combining the 1.6 GHz VSOP image with the 5.0 GHz VLBA+Y image at the first epoch is also presented.

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Does the Magnetodynamic Model for the Formation of AGN Jets Survive New Findings of High-energy Phenomena near the Central Objects?

Symposium - International Astronomical Union ◽

10.1017/s007418090016351x ◽

2000 ◽

Vol 195 ◽

pp. 473-481

Author(s):

Y. Uchida

Keyword(s):

Lorentz Factor ◽

High Energy ◽

Major Effect ◽

Alfven Wave ◽

Poynting Flux ◽

Central Engine ◽

New Findings ◽

Wave Trains ◽

Kink Instability ◽

Jet Structure

Here, we argue that, despite all-new findings of phenomena with very large Lorentz factors, the importance of the magnetodynamic process accelerating and collimating AGN jets should not be affected because there exists evidence in the features of the jets and tails at large distances indicating that the wiggles of the jet structure are likely to be due to a magnetic, helical kink instability. These systematic features require too much energy and coherence of the driving process to be produced locally and axe most naturally produced by a magnetic effect coming from the powerful central engine. This indicates that the major effect producing the jets, and the lobes with hotspots at the tips of the jets, is likely to be the Poynting flux carried by torsional Alfvén wave trains plus the re-accelerated high-energy particles in them. The very large Lorentz-factor phenomena should not hinder the transfer of these magnetic effects and are likely to be byproducts of the basic magnetodynamic process, and not the reverse.

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Giant radio galaxies in the LOFAR Two-metre Sky Survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935589 ◽

2020 ◽

Vol 635 ◽

pp. A5 ◽

Cited By ~ 9

Author(s):

P. Dabhade ◽

H. J. A. Röttgering ◽

J. Bagchi ◽

T. W. Shimwell ◽

M. J. Hardcastle ◽

...

Keyword(s):

Spectral Index ◽

Radio Galaxy ◽

Radio Galaxies ◽

Large Sample ◽

Search Techniques ◽

Sky Survey ◽

Data Release ◽

Cluster Environment ◽

First Time

Giant radio galaxies (GRGs) are a subclass of radio galaxies, which have grown to megaparsec scales. GRGs are much rarer than normal-sized radio galaxies (< 0.7 Mpc) and the reason for their gigantic sizes is still debated. Here, we report on the biggest sample of GRGs identified to date. These objects were found in the LOFAR Two-metre Sky Survey first data release images, which cover a 424 deg2 region. Of the 239 GRGs found, 225 are new discoveries. The GRGs in our sample have sizes ranging from 0.7 Mpc to 3.5 Mpc and have redshifts (z) between 0.1 and 2.3. Seven GRGs have sizes above 2 Mpc and one has a size of ∼3.5 Mpc. The sample contains 40 GRGs hosted by spectroscopically confirmed quasars. Here, we present the search techniques employed and the resulting catalogue of the newly discovered large sample of GRGs along with their radio properties. In this paper, we also show for the first time that the spectral index of GRGs is similar to that of normal-sized radio galaxies, indicating that most of the GRG population is not dead or is not similar to a remnant-type radio galaxy. We find that 20 out of 239 GRGs in our sample are located at the centres of clusters and we present our analysis on their cluster environment and radio morphology.

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Diffusion and advection model for particle transport in young pulsar wind nebulae

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312023812 ◽

2012 ◽

Vol 8 (S291) ◽

pp. 265-268

Author(s):

Xiaping Tang ◽

Roger A. Chevalier

Keyword(s):

Spectral Index ◽

Particle Transport ◽

Crab Nebula ◽

Outer Boundary ◽

Outer Part ◽

Pulsar Wind Nebulae ◽

Pure Diffusion ◽

Pulsar Wind ◽

Kink Instability ◽

The Crab Nebula

AbstractThe magnetohydrodynamic (MHD) model for young pulsar wind nebulae (PWN) has been successful in reproducing many features of the nebulae. The model is characterized by a termination shock (TS) between the PWN and unshocked pulsar wind. Relativistic particles are injected at the TS and follow an advective flow to the outer boundary. However, toroidal structure of well studied young PWN like the Crab Nebula, 3C 58 and G21.5-0.9 is only present in the region close to the TS. In the outer parts of the nebulae, filamentary and loop-like structure is observed. Also, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that a pure diffusion model with energy independent diffusion and a transmitting boundary can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5-0.9. Energy dependent diffusion is also discussed. Power law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state case. Monte Carlo simulations of particle transport with both diffusion and advection for the Crab nebula and 3C 58 suggest a picture in which advection dominates the inner part of the PWN where toroidal structure is clearly present. Diffusion dominates the outer part of the PWN where filamentary and loop-like structure is observed. The source of the chaotic field is uncertain, but may be related to Rayleigh-Taylor instability at the outer boundary of young nebulae and/or the kink instability of the toroidal magnetic field.

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Revealing hidden variability in PWNe with spectral index maps

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2364 ◽

2020 ◽

Vol 498 (1) ◽

pp. 821-834

Author(s):

Benson T Guest ◽

Samar Safi-Harb

Keyword(s):

Spectral Index ◽

Rotational Energy ◽

Line Of Sight ◽

Pulsar Wind Nebulae ◽

X Ray ◽

Analysis Technique ◽

Intrinsic Motion ◽

Pulsar Wind ◽

Map Analysis ◽

Index Maps

ABSTRACT Pulsar wind nebulae (PWNe) are the synchrotron bubbles inflated by the rotational energy of a neutron star. Observing variability within them has previously been limited to cases of significant brightening, or the few instances where transient features are interpreted in terms of intrinsic motion or associated with variability from the pulsar. Jet and torus morphology are also only visible in cases of differing brightness with respect to the surrounding nebula and favourable alignment with our line of sight. Spectral map analysis involves binning observations with an adaptive algorithm to meet a signal limit and colouring the results based on the desired model parameter fits. Minute changes in spectral index become therefore apparent even in cases where brightness images alone do not suggest any underlying changes. We present a Chandra X-ray study of the PWNe in G21.5–0.9, Kes 75, G54.1+0.3, G11.2–0.3, and 3C 58, using archival observations accumulated over the ∼20-yr lifetime of the mission. With the spectral map analysis technique, we discover evidence for previously unknown variability opening a new window into viewing PWNe.

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Twisted Jets from L1551 IRS5

Symposium - International Astronomical Union ◽

10.1017/s0074180900225291 ◽

2001 ◽

Vol 200 ◽

pp. 261-264

Author(s):

Yoichi Itoh

Keyword(s):

Infrared Spectroscopy ◽

High Resolution ◽

Spatial Variation ◽

Near Infrared Spectroscopy ◽

Near Infrared ◽

Infrared Imaging ◽

Close Vicinity ◽

Jet Structure ◽

First Time ◽

Bright Emission

We have carried out high-resolution near-infrared imaging observations of a protostar L1551 IRS 5 with the Subaru Telescope. The jet structure of IRS5 is resolved into two independent jets for the first time from the ground. Successive near-infrared spectroscopy has revealed that the jet emission is dominated by [Fe II] lines in the J and H-bands. While the visual-extinction reaches more than 20 mag in the close vicinity of IRS 5, it decreases rapidly at ∼1″ from IRS 5 and remains constant around 7 mag at larger distances. The twisted structure and bright emission knots are intrinsic to the jets, not due to a spatial variation of the extinction.

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Multi-Array λ2 and 6cm Radio Continuum Observations of Sgr A West

Symposium - International Astronomical Union ◽

10.1017/s0074180900186875 ◽

1989 ◽

Vol 136 ◽

pp. 443-451 ◽

Cited By ~ 3

Author(s):

F. Yusef-Zadeh ◽

Mark Morris ◽

Ron Ekers

Keyword(s):

Spectral Index ◽

Stellar Wind ◽

Galactic Center ◽

Radio Continuum ◽

Continuum Emission ◽

Spectral Indices ◽

Ionized Gas ◽

Sgr A ◽

Index Maps ◽

East West

Sub-arcsecond (down to 0.1″ × 0.2″) radio continuum observations using the VLA2 in a number of configurations have been carried out in order to investigate the fine-scale morphological details of the ionized gas and the distribution of spectral index along the triskelian-shaped figure of Sgr A West. In addition to finding a number of isolated patches of thermally-emitting gas and an absorbing feature at λ6cm within three arcminutes of the Galactic center, we have observed:1) radio continuum emission from IRS-7, implying that the stellar wind from this supergiant is externally ionized. An improved position for this object was obtained.2) the circular mini-cavity located along the east-west bar of Sgr A West. This feature has a diameter of 2-arcseconds and may have been created by a spherical wind, the source of which is yet to be identified; the seemingly most plausible candidate, IRS-16, is offset by 3″ from the center of the cavity.Spectral index maps having a resolution of 0.7″ × 0.3″ were made from scaled array observations at λ2cm and 6cm. They show that the eastern arm has a spectral index near −0.1, while the northern arm and the bar have positive spectral indices, indicating perhaps a partial opacity effect. The spectral index of IRS-7 is +0.6, consistent with that expected from a completely ionized stellar wind.

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