Spectral index maps of the radio halos in Abell 665 and Abell 2163

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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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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VIMAP: AN INTERACTIVE PROGRAM PROVIDING RADIO SPECTRAL INDEX MAPS OF ACTIVE GALACTIC NUCLEI

Journal of The Korean Astronomical Society ◽

10.5303/jkas.2014.47.5.195 ◽

2014 ◽

Vol 47 (5) ◽

pp. 195-199 ◽

Cited By ~ 7

Author(s):

Jae-Young Kim ◽

Sascha Trippe

Keyword(s):

Active Galactic Nuclei ◽

Spectral Index ◽

Galactic Nuclei ◽

Interactive Program ◽

Index Maps

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Revealing dust segregation in protoplanetary discs with the help of multifrequency spectral index maps

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1046 ◽

2019 ◽

Vol 486 (3) ◽

pp. 3907-3914 ◽

Cited By ~ 4

Author(s):

Yaroslav Pavlyuchenkov ◽

Vitaly Akimkin ◽

Dmitri Wiebe ◽

Eduard Vorobyov

Keyword(s):

Spectral Index ◽

Index Maps ◽

Protoplanetary Discs

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1038+528 A, B: Phase-Reference and Spectral-Index Maps

Symposium - International Astronomical Union ◽

10.1017/s0074180900078165 ◽

1984 ◽

Vol 110 ◽

pp. 247-248

Author(s):

J. Marcaide ◽

I. Shapiro ◽

N. Cohen ◽

B. Corey ◽

W. Cotton ◽

...

Keyword(s):

Circular Polarization ◽

Spectral Index ◽

Reference Point ◽

Reference Points ◽

Vlbi Observations ◽

Structure Phase ◽

Propagation Medium ◽

Image Position ◽

Index Maps

On 1981 March 17–18 we undertook MkIII VLBI observations of the quasars 1038+528 A, B (Owen et al. 1979; Owen et al. 1980) with an array of 7 telescopes operating simultaneously at λ3.6 and λ13 cm with right circular polarization reception at each wavelength. Because the sources are ~33″ apart they could be observed simultaneously at every telescope. Thus the corrupting contributions of the propagation medium and the instrumentation were approximately the same for each of the quasars, hence allowing us to calibrate the structure phase of B with respect to a reference point chosen in the map of A using the expression where φB and φA are the observed fringe phases, φGB and φGA are the geometric contribution with respect to the reference points chosen in each map and φSA is the structure phase contribution with respect to the reference point chosen in the A map.

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Asymmetric jet production in the active galactic nucleus of NGC 1052

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833828 ◽

2019 ◽

Vol 623 ◽

pp. A27 ◽

Cited By ~ 5

Author(s):

A.-K. Baczko ◽

R. Schulz ◽

M. Kadler ◽

E. Ros ◽

M. Perucho ◽

...

Keyword(s):

Spectral Index ◽

Jet Flows ◽

Central Feature ◽

Long Baseline ◽

Inclination Angles ◽

Moving Jet ◽

Thick Absorber ◽

Density Ratios ◽

Very Long Baseline Array ◽

Index Maps

Context. Few active galactic nuclei (AGN) reveal double-sided jet systems. However, these systems are crucial to understand basic physical properties of extragalactic jets. Aims. We address the questions whether jets in AGN are symmetric in nature, how well they are collimated on small scales, and how they evolve with time. Methods. We monitored the sub-parsec scale morphology of NGC 1052 with the Very Long Baseline Array at 43 GHz from 2005 to 2009. Results. A detailed study of 29 epochs show a remarkable asymmetry between both jets. A kinematic analysis of the outflows reveals higher apparent velocities for the eastern (approaching) jet as compared to the western (receding) jet, i.e., βej = 0.529 ± 0.038 and βwj = 0.343 ± 0.037, respectively. Contradictory to previous studies, we find higher flux densities for the western jet as compared to the eastern. The distribution of brightness temperature and jet width features well-collimated jets up to 1 mas distance to the dynamic center and a nearly conical outflow further outward. By combining flux density ratios and velocities of the jet flows, we were unable to find a combination of intrinsic velocities and inclination angles of the jets that is consistent for all four years of observation; this contradicts findings for symmetrically evolving jets. Spectral index maps between quasi-simultaneous 22 GHz and 43 GHz observations support the existence of an optically thick absorber covering the innermost ≃1.6 mas around the 43 GHz central feature and an optically thin jet emission with a spectral index of ≤−1. Conclusions. Our results fit into a picture in which we expect larger internal energy and/or magnetic flux in the western jet and higher kinetic energy in the eastern jet. Previous observations at lower frequencies have found slower velocities of the moving jet features as compared to this work. Considering the different velocities in different areas, we suggest a spine-sheath structure with a faster inner layer and slower outer layer.

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The discovery of radio halos in the frontier fields clusters Abell S1063 and Abell 370

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936953 ◽

2020 ◽

Vol 636 ◽

pp. A3 ◽

Cited By ~ 3

Author(s):

C. Xie ◽

R. J. van Weeren ◽

L. Lovisari ◽

F. Andrade-Santos ◽

A. Botteon ◽

...

Keyword(s):

Spectral Index ◽

Relativistic Electrons ◽

Synchrotron Emission ◽

Scaling Relation ◽

Diffuse Emission ◽

Very Large Array ◽

X Ray ◽

Radio Halo ◽

Radio Power ◽

Radio Halos

Context. Massive merging galaxy clusters often host diffuse megaparsec-scale radio synchrotron emission. This emission originates from relativistic electrons in the ionized intracluster medium. An important question is how these synchrotron emitting relativistic electrons are accelerated. Aims. Our aim is to search for diffuse emission in the Frontier Fields clusters Abell S1063 and Abell 370 and characterize its properties. While these clusters are very massive and well studied at some other wavelengths, no diffuse emission has been reported for these clusters so far. Methods. We obtained 325 MHz Giant Metrewave Radio Telescope (GMRT) and 1–4 GHz Jansky Very Large Array (VLA) observations of Abell S1063 and Abell 370. We complement these data with Chandra and XMM-Newton X-ray observations. Results. In our sensitive images, we discover radio halos in both clusters. In Abell S1063, a giant radio halo is found with a size of ∼1.2 Mpc. The integrated spectral index between 325 MHz and 1.5 GHz is −0.94 ± 0.08 and it steepens to −1.77 ± 0.20 between 1.5 and 3.0 GHz. This spectral steepening provides support for the turbulent reacceleration model for radio halo formation. Abell 370 hosts a faint radio halo mostly centered on the southern part of this binary merging cluster, with a size of ∼500−700 kpc. The spectral index between 325 MHz and 1.5 GHz is −1.10 ± 0.09. Both radio halos follow the known scaling relation between the cluster mass proxy Y500 and radio power, which is consistent with the idea that they are related to ongoing cluster merger events.

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High-Resolution Radio Observations of the Crablike Supernova Remnant 3C 58

Symposium - International Astronomical Union ◽

10.1017/s0074180900160589 ◽

1987 ◽

Vol 125 ◽

pp. 123-123

Author(s):

Stephen P. Reynolds ◽

H. D. Aller

Keyword(s):

Point Source ◽

Spectral Index ◽

Position Angle ◽

Particle Energy ◽

Shock Acceleration ◽

Very Large Array ◽

The North ◽

South Central ◽

Entropy Technique ◽

Index Maps

We report Very Large Array1 observations of 3C 58, the Crab Nebula's closest relative at radio wavelengths. We combined A, B, C, and D configurations (baselines ranging from 0.08 to 35 km) at frequencies of 1446 MHz and 4886 MHz, achieving resolutions of 1″.9 and 2″.5, respectively, and a sensitivity at both frequencies of about 70 μJy per beam. We deconvolved the point-source response from the images using a maximum-entropy technique. The 1446 MHz total-intensity image shows that filamentation not only dominates the spatial distribution of flux in the bright inner regions, but appears to continue into the faint outer envelope as well. This envelope fades smoothly into the noise over about half the circumference of the remnant; the lowest contours of our map show maximum extents in RA and δ of 10′.3 and 6′.3 respectively. However, in some places the edge is relatively well-defined, suggesting confinement of some kind. A remarkably jet-like extension can be seen protruding from the south central part of the remnant, with a position angle of about 150° with respect to the radio peak. Unlike the Crab's jet, this is wedge-shaped and somewhat resembles the brighter extension to the north. The X-ray point source (Becker, Helfand, and Szymkowiak 1982, Ap. J. 255, 557) lies about 30″ east of the peak in the radio map. No obvious radio feature coincides with it. We have made spectral-index maps of the remnant, and find only small variations, with little apparent correlation of spectral index with structure. The rms deviation from the remnant mean spectral index is 0.18, but profiles of filaments show less than 0.1 difference in spectral index between peaks and adjacent valleys. Thus the bright filaments are neither flatter nor steeper in spectrum than the remnant mean, ruling out a picture in which bright filaments are locations where shock acceleration produces a steeper particle energy spectrum. Filaments have brightness contrasts of factors of 1.5 to 2, steep edges (<10″, sometimes unresolved) and widths of 10″–30″; if they have similar thicknesses along the line of sight, their emissivity ranges up to 40–50 times the remnant mean.

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