scholarly journals Radio polarization observations of large supernova remnants at λ6 cm

2013 ◽  
Vol 9 (S296) ◽  
pp. 202-209 ◽  
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.

scholarly journals Probing interstellar magnetic fields with Supernova remnants

2008 ◽  
Vol 4 (S259) ◽  
pp. 75-80 ◽  
Author(s):  
Roland Kothes ◽  
Jo-Anne Brown
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Galactic Plane ◽  
Field Configuration ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
Field Lines ◽  
The Magnetic Field

AbstractAs Supernova remnants expand, their shock waves are freezing in and compressing the magnetic field lines they encounter; consequently we can use Supernova remnants as magnifying glasses for their ambient magnetic fields. We will describe a simple model to determine emission, polarization, and rotation measure characteristics of adiabatically expanding Supernova remnants and how we can exploit this model to gain information about the large scale magnetic field in our Galaxy. We will give two examples: The SNR DA530, which is located high above the Galactic plane, reveals information about the magnetic field in the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre of our Galaxy and reveals the most probable direction where the large-scale magnetic field is perpendicular to the line of sight. This may help to decide on the large-scale magnetic field configuration of our Galaxy. But more observations of SNRs are needed.

scholarly journals 8·8 GHz Radio Observations of 12 Suggested Supernova Remnants

1973 ◽  
Vol 26 (3) ◽  
pp. 379 ◽  
Author(s):  
JR Dickel ◽  
DK Milne ◽  
AR Kerr ◽  
JG Ables
Keyword(s):  
Flux Density ◽  
Supernova Remnants ◽  
Supernova Remnant ◽  
Galactic Plane ◽  
Small Diameter ◽  
Radio Sources ◽  
Radio Observations ◽  
Frequency Measurements ◽  
Thermal Spectrum

Brightness distributions and flux densities at 8�8 GHz are presented for 12 small-diameter radio sources near the galactic plane. Each of these sources has been classified at one time or another as a supernova remnant. For one source, G295� 2 - 0�6, the flux density at 8�8 GHz confirms the thermal spectrum suggested by lower frequency measurements and indicates that it is not a supernova remnant. Another source, G309� 6+ 1�7, is thought to be extragalactic.

scholarly journals Radio Emission from the Supernova Remnant Vela-X

1968 ◽  
Vol 21 (2) ◽  
pp. 201 ◽  
Author(s):  
DK Milne
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Radio Emission ◽  
Spectral Index ◽  
Supernova Remnants ◽  
Supernova Remnant ◽  
Magnetic Field Direction ◽  
Radio Observations ◽  
Optical Identification ◽  
Polarization Measurements

Radio observations are presented of the fairly large galactic complex Vela-X, Y, and Z. These sources are believed to be the remnant of a supernova having an optical identification with the filamentary nebula Stromlo 16. The brightness distributions, obtained at four frequencies, indicate an open annular structure reminiscent of other supernova remnants. The variation of spectral index over the region is investigated and shows that the radiation is substantially nontherm81, the integrated fluxes yielding a spectral index of -0,3. A high resolution distribution of magnetic field direction is deduced from polarization measurements made at three frequencies; a circumferential magnetic field is a possible interpretation of the field orientations.

scholarly journals The modified equipartition calculation for supernova remnants with the spectral index α = 0.5

2012 ◽  
Vol 10 (H16) ◽  
pp. 398-398
Author(s):  
Dejan Urošević ◽  
Marko Z. Pavlović ◽  
Bojan Arbutina ◽  
Aleksandra Dobardžić
Keyword(s):  
Magnetic Field ◽  
Spectral Index ◽  
Analytical Method ◽  
Supernova Remnants ◽  
Spectral Indices ◽  
The Magnetic Field ◽  
Field Strengths

AbstractRecently, the modified equipartition calculation for supernova remnants (SNRs) has been derived by Arbutina et al. (2012). Their formulae can be used for SNRs with the spectral indices between 0.5 < α < 1. Here, by using approximately the same analytical method, we derive the equipartition formulae useful for SNRs with spectral index α=0.5. These formulae represent next step upgrade of Arbutina et al. (2012) derivation, because among 30 Galactic SNRs with available observational parameters for the equipartition calculation, 16 have spectral index α = 0.5. For these 16 Galactic SNRs we calculated the magnetic field strengths which are approximately 40 per cent higher than those calculated by using Pacholczyk (1970) equipartition and similar to those calculated by using Beck & Krause (2005) calculation.

scholarly journals Updated radio Σ−D relation for galactic supernova remnants

2014 ◽  
pp. 25-40 ◽  
Author(s):  
M.Z. Pavlovic ◽  
A. Dobardzic ◽  
B. Vukotic ◽  
D. Urosevic
Keyword(s):  
Supernova Remnants ◽  
Galactic Plane ◽  
Empirical Relation ◽  
Data Sets ◽  
Orthogonal Regression ◽  
Fitting Procedure ◽  
Density Maps ◽  
Calibration Sample ◽  
Data Points ◽  
First Time

We present the updated empirical radio surface-brightness-to-diameter (? ? D) relation for supernova remnants (SNRs) in our Galaxy. Our original calibration sample of Galactic SNRs with independently determined distances (Pavlovic et al. 2013, hereafter Paper I) is reconsidered and updated with data which became available in the past two years. The orthogonal fitting procedure and probability-density-function-based (PDF) method are applied to the calibration sample in the log? ? logD plane. Non-standard orthogonal regression keeps the ??D and D?? relations invariant within estimated uncertainties. Our previous Monte Carlo simulations verified that the slopes of the empirical ??D relation should be determined by using the orthogonal regression, because of its good performances for data sets with severe scatter. The updated calibration sample contains 65 shell SNRs. 6 new Galactic SNRs are added to the sample from Paper I, one is omitted and distances are changed for 10 SNRs. The slope derived is here slightly steeper (? ? 5.2) than the ??D slope in Paper I (? ? 4.8). The PDF method relies on data points density maps which can provide more reliable calibrations that preserve more information contained in the calibration sample. We estimate distances to five new faint Galactic SNRs discovered for the first time by Canadian Galactic Plane Survey, and obtained distances of 2.3, 4.0, 1.3, 2.9 and 4.7 kiloparsecs for G108.5+11.0, G128.5+2.6, G149.5+3.2, G150.8+3.8 and G160.1?1.1, respectively. The updated empirical relation is used to estimate distances of 160 shell Galactic SNRs and new results change their distance scales up to 15 per cent, compared to the results from Paper I. The PDF calculation can provide even few times higher or lower values in comparison with the orthogonal fit, as it uses a totally different approach. However, on average, this difference is 32, 24 and 18 per cent for mode, median and mean distances.

scholarly journals Observations of Magnetic Fields in Galaxies

1992 ◽  
Vol 9 ◽  
pp. 81-86
Author(s):  
R. Wielebinski
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Galactic Plane ◽  
Building Blocks ◽  
Galactic Centre ◽  
Definitive Evidence ◽  
The Galaxy ◽  
The Universe

AbstractMagnetic fields are present in every corner of the Universe. The Earth, the Sun and most of the planets are known to possess dipolar magnetic fields. In the Galaxy many individual objects like stars, pulsars, bipolar nebulae and supernova remnants are found to have associated magnetic fields. It seems that the rotation plays a significant role in the ability of a cosmic object to develop a magnetic field. The magnetic field of the Galaxy is observed to be oriented along the galactic plane as evidenced by both optical and radio polarization observations. Radio maps of the Galactic centre reveal poloidal magnetic fields as ‘wisps’ or ‘strings’ around Sagittarius A. Observations of nearby galaxies give us remarkable information about the large-scale magnetic fields in these building blocks of the Universe. Magnetic fields play an important role in the formation of jets of radio galaxies. Further out, in clusters of galaxies, definitive evidence has been given for the existence of intergalactic magnetic fields.

scholarly journals A low-frequency view of mixed-morphology supernova remnant VRO 42.05.01, and its neighbourhood

2019 ◽  
Vol 622 ◽  
pp. A6 ◽  
Author(s):  
M. Arias ◽  
J. Vink ◽  
M. Iacobelli ◽  
V. Domček ◽  
M. Haverkorn ◽  
...  
Keyword(s):  
Spectral Index ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Low Frequency ◽  
Radio Spectrum ◽  
Optical Data ◽  
Shock Acceleration ◽  
H Ii Region ◽  
Radio Frequencies ◽  
Index Value

Context. Mixed-morphology supernova remnants (MM SNRs) are a mysterious class of objects that display thermal X-ray emission within their radio shell. They are an older class of SNRs, and as such are profoundly affected by the environment into which they evolve. VRO 42.05.01 is a MM SNR of puzzling morphology in the direction of the Galactic anticentre. Aims. Low-frequency radio observations of supernova remnants are sensitive to synchrotron electrons accelerated in the shock front. We aim to compare the low-frequency emission to higher frequency observations to understand the environmental and shock acceleration conditions that have given rise to the observed properties of this source. Methods. We present a LOFAR High Band Antenna map centred at 143 MHz of the region of the Galactic plane centred at l = 166 ° ,  b = 3.5° at 143 MHz, with a resolution of 148″ and an rms noise of 4.4 mJy bm−1. Our map is sensitive to scales as large as 6°. We compared the LOw Frequency ARay (LOFAR) observations to archival higher frequency radio, infrared, and optical data to study the emission properties of the source in different spectral regimes. We did this both for the SNR and for OA 184, an H II region within our field of view. Results. We find that the radio spectral index of VRO 42.05.01 increases at low radio frequencies; i.e. the LOFAR flux is higher than expected from the measured spectral index value at higher radio frequencies. This observed curvature in the low-frequency end of the radio spectrum occurs primarily in the brightest regions of the source, while the fainter regions present a roughly constant power-law behaviour between 143 MHz and 2695 MHz. We favour an explanation for this steepening whereby radiative shocks have high compression ratios and electrons of different energies probe different length scales across the shocks, therefore sampling regions of different compression ratios.

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

Galaxies ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 86 ◽  
Author(s):  
Wei Zhao ◽  
Xiaoyu Hong ◽  
Tao An ◽  
Xiaofeng Li ◽  
Xiaopeng Cheng ◽  
...  
Keyword(s):  
Spectral Index ◽  
External Medium ◽  
Spatial Association ◽  
Local Enhancement ◽  
Transverse Jet ◽  
Kink Instability ◽  
Index Maps ◽  
Jet Structure ◽  
First Time

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.

scholarly journals Galactic Supernova Remnants: Radio Evolution and Population Characteristics

1979 ◽  
Vol 32 (2) ◽  
pp. 79 ◽  
Author(s):  
JL Caswell ◽  
I Lerche
Keyword(s):  
Magnetic Field ◽  
Supernova Remnants ◽  
Surface Brightness ◽  
Birth Rate ◽  
Galactic Plane ◽  
Scale Height ◽  
Population Characteristics ◽  
Cumulative Number ◽  
Number Count ◽  
Height Dependence

Shell SNRs show a systematic gradient of radio surface brightness normal to the galactic plane, and a measured scale height for this effect has been obtained. The progenitor distribution and birth rate are significantly modified when allowance is made for this effect. The galactic height dependence of radio surface brightness satisfactorily accounts for the otherwise anomalous highlatitude SNR AD 1006. It also provides a crucial clue to the origin of the radio emission, suggesting that the interstellar magnetic field is dominant over internally generated fields in shell SNRs. Recently we have independently reached the same conclusion from a consideration of the cumulative number count of shell SNRs.

scholarly journals Investigation of the double-lobed sources of the Cygnus constellation core

2021 ◽  
Vol 38 ◽  
Author(s):  
J. Saponara ◽  
P. Benaglia ◽  
I. Andruchow ◽  
C. H. Ishwara-Chandra ◽  
H. T. Intema
Keyword(s):  
Spectral Index ◽  
Angular Resolution ◽  
Galactic Plane ◽  
Central Nucleus ◽  
Electromagnetic Spectrum ◽  
Large Area ◽  
X Ray ◽  
First Results ◽  
First Time ◽  
Better Than

Abstract We present a collection of double-lobed sources towards a $20\,\mathrm{deg}^2$ area of the Cygnus region at the northern sky, observed at 325 and 610 MHz with the Giant Metrewave Radio Telescope. The 10 $^{\prime\prime}$ resolution achieved at 325 MHz is 5.5 times better than previous studies, while at 610 MHz, these are the first results ever of such a large area, mapped with 6 $^{\prime\prime}$ angular resolution. After a thorough visual inspection of the images at the two bands, we found 43 double-lobed source candidates, proposed as such due to the presence of 2 bright peaks, within a few arcminutes apart, joined by a bridge or a central nucleus. All but two are presented here as a double-lobed candidates for the first time. Thirty nine of the candidates were covered at both bands, and we provide the spectral index information for them. We have searched for positional coincidences between the detected sources/components and other objects from the literature, along the electromagnetic spectrum. Twenty-three candidates possess radio counterpart(s), 12 present infrared counterparts, and 1 showed an overlapping X-ray source. We analysed each candidate considering morphology, counterparts, and spectral indices. Out of the 43 candidates, 37 show characteristics compatible with an extragalactic nature, 2 of probably Galactic origin, 3 remain as dubious cases, though with feature(s) compatible with an extragalactic nature, and the remaining one, evidence of physically unrelated components. The median spectral index of the 40 putative extragalactic sources is $-1.0$ . Their celestial surface density at 610 MHz resulted in $1.9\,\mathrm{per\ deg}^2$ , across a region lying at the Galactic plane.

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