Quiescent Non-thermal Radio Emission from Stellar Systems

1995 ◽  
Vol 12 (2) ◽  
pp. 174-179 ◽  
Author(s):  
Michelle C. Storey ◽  
R. G. Hewitt
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Three Dimensional ◽  
Emission Region ◽  
Relativistic Electrons ◽  
Thermal Radio ◽  
T Tauri ◽  
Thermal Radio Emission ◽  
Magnetic Field Model ◽  
Gyrosynchrotron Emission

AbstractNon-thermal radio emission has been detected from dMe stars, RS CVn binaries and W T Tauri stars. Polarisation and intensity measurements of the quiescent (i.e. non-flaring) emission indicate that the emission is gyrosynchrotron emission from mildly relativistic electrons spiralling in a magnetic field. A three-dimensional dipole magnetic field model for the stellar field is presented and the quiescent gyrosynchrotron emission from such a model is calculated and compared with observations. The model can account for many phenomenological features of quiescent emission. Quantitative comparisons of model results with observations indicate that the electron distribution in the emission region may be a magnetic mirroring distribution.

scholarly journals The nearby extreme accretion and feedback system PDS 456: finding a complex radio-emitting nucleus

2020 ◽  
Vol 500 (2) ◽  
pp. 2620-2626
Author(s):  
Jun Yang ◽  
Zsolt Paragi ◽  
Emanuele Nardini ◽  
Willem A Baan ◽  
Lulu Fan ◽  
...  
Keyword(s):  
Black Hole ◽  
Radio Emission ◽  
High Speed ◽  
Feedback System ◽  
Emission Region ◽  
Starburst Galaxy ◽  
Massive Black Hole ◽  
Star Forming ◽  
Thermal Radio ◽  
Thermal Radio Emission

ABSTRACT When a black hole accretes close to the Eddington limit, the astrophysical jet is often accompanied by radiatively driven, wide-aperture and mildly relativistic winds. Powerful winds can produce significant non-thermal radio emission via shocks. Among the nearby critical accretion quasars, PDS 456 has a very massive black hole (about 1 billion solar masses), shows a significant star-forming activity (about 70 solar masses per year), and hosts exceptionally energetic X-ray winds (power up to 20 per cent of the Eddington luminosity). To probe the radio activity in this extreme accretion and feedback system, we performed very long baseline interferometric (VLBI) observations of PDS 456 at 1.66 GHz with the European VLBI Network and the enhanced Multi-Element Remotely Linked Interferometry Network. We find a rarely seen complex radio-emitting nucleus consisting of a collimated jet and an extended non-thermal radio emission region. The diffuse emission region has a size of about 360 pc and a radio luminosity about three times higher than that of the nearby extreme starburst galaxy Arp 220. The powerful nuclear radio activity could result either from a relic jet with a peculiar geometry (nearly along the line of sight) or more likely from diffuse shocks formed naturally by the existing high-speed winds impacting on high-density star-forming regions.

scholarly journals Can the Local Bubble explain the radio background?

2021 ◽  
Vol 502 (2) ◽  
pp. 2807-2814
Author(s):  
Martin G H Krause ◽  
Martin J Hardcastle
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Radio Emission ◽  
Magnetic Energy ◽  
Cosmic Ray ◽  
Observational Constraints ◽  
Local Bubble ◽  
Magnetic Energy Density ◽  
Magnetic Field Model ◽  
Radio Background

ABSTRACT The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3 and 5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarization. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2−0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.

scholarly journals High-sensitivity radio study of the non-thermal stellar bow shock EB27

2021 ◽  
Author(s):  
Paula Benaglia ◽  
Santiago del Palacio ◽  
Christopher Hales ◽  
Marcelo E Colazo
Keyword(s):  
Radio Emission ◽  
Massive Star ◽  
High Sensitivity ◽  
Bow Shock ◽  
Relativistic Electrons ◽  
Polarimetric Observation ◽  
Very Large Array ◽  
Thermal Radio Emission ◽  
The Magnetic Field ◽  
Linear Polarisation

Abstract We present a deep radio-polarimetric observation of the stellar bow shock EB27 associated to the massive star BD+43○3654. This is the only stellar bow shock confirmed to have non-thermal radio emission. We used the Jansky Very Large Array in S band (2–4 GHz) to test whether this synchrotron emission is polarised. The unprecedented sensitivity achieved allowed us to map even the fainter regions of the bow shock, revealing that the more diffuse emission is steeper and the bow shock brighter than previously reported. No linear polarisation is detected in the bow shock above 0.5%, although we detected polarised emission from two southern sources, probably extragalactic in nature. We modeled the intensity and morphology of the radio emission to better constrain the magnetic field and injected power in relativistic electrons. Finally, we derived a set of more precise parameters for the system EB27–BD+43○3654 using Gaia Early Data Release 3, including the spatial velocity. The new trajectory, back in time, intersects the core of the Cyg OB2 association.

Resonance effects in thermal radio emission of water surface

1986 ◽  
Vol 29 (4) ◽  
pp. 279-283 ◽  
Author(s):  
V. E. Gershenzon ◽  
V. G. Irisov ◽  
Yu. G. Trokhimovskii ◽  
V. S. �tkin
Keyword(s):  
Radio Emission ◽  
Water Surface ◽  
Resonance Effects ◽  
Thermal Radio ◽  
Thermal Radio Emission

scholarly journals Non-thermal radio emission from O-type stars

2007 ◽  
Vol 464 (2) ◽  
pp. 701-708 ◽  
Author(s):  
R. Blomme ◽  
M. De Becker ◽  
M. C. Runacres ◽  
S. Van Loo ◽  
D. Y. A. Setia Gunawan
Keyword(s):  
Radio Emission ◽  
Thermal Radio ◽  
Thermal Radio Emission

scholarly journals Erratum: Constraining the nature of DG Tau A's thermal and non-thermal radio emission

2018 ◽  
Vol 483 (3) ◽  
pp. 4085-4085
Author(s):  
S J D Purser ◽  
R E Ainsworth ◽  
T P Ray ◽  
D A Green ◽  
A M Taylor ◽  
...  
Keyword(s):  
Radio Emission ◽  
Thermal Radio ◽  
Thermal Radio Emission

scholarly journals Radio Emission from Flares in Single Late-type Stars

1995 ◽  
Vol 151 ◽  
pp. 22-31
Author(s):  
Arnold O. Benz
Keyword(s):  
Radio Emission ◽  
High Energy ◽  
Primary Energy ◽  
Relativistic Electrons ◽  
Late Type ◽  
Loss Cone ◽  
Magnetically Trapped ◽  
Stellar Flares ◽  
Gyrosynchrotron Emission ◽  
M Stars

AbstractRadio observations provide the most direct information on non-thermal electrons in stellar flares and in the coronae of late-type stars. Radio emissions of single main-sequence F, G, and of many K stars have recently been discovered, in addition to the well-known dwarf M stars. Their long-duration radio flares with low circular polarization, slow variations and broad bandwidth can be attributed to gyrosynchrotron emission of mildly relativistic electrons. The same holds for the low-level (‘quiescent’) radio emission. On the other hand, highly polarized radio flares of M stars have been interpreted by coherent emissions from loss-cone instabilities of magnetically trapped electrons. These conjectures are consistent with recent VLBI observations. The identification of the radio emission process allows to estimate the high-energy component of the flare and compare it to the total flare energy. The weakly polarized radio emission may serve as a proxy for hard X-ray signatures of relativistic electrons. The fraction of primary energy released into energetic electrons then appears to be large and similar to solar flares.

scholarly journals Non-thermal radio emission in Wolf-Rayet stars: is binarity a pre-requisite?

1999 ◽  
Vol 193 ◽  
pp. 348-349
Author(s):  
Sean M. Dougherty
Keyword(s):  
Radio Emission ◽  
Spectral Index ◽  
Thermal Emission ◽  
Radio Observations ◽  
Thermal Radio ◽  
Thermal Radio Emission ◽  
Thermal Emitters

Radio observations of Wolf-Rayet stars currently available in the literature are examined to determine whether binarity is a common feature of WR systems with non-thermal emission. Among 24 stars with observed spectral index values, seven are definite non-thermal emitters, and six others possibly have composite thermal/non-thermal spectra. Stellar companions have been identified in 71% of the non-thermal emitters, strongly supporting a link between non-thermal emission and binarity.

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