scholarly journals Classical Novae at Radio Wavelengths

2021 ◽  
Vol 257 (2) ◽  
pp. 49
Author(s):  
Laura Chomiuk ◽  
Justin D. Linford ◽  
Elias Aydi ◽  
Keith W. Bannister ◽  
Miriam I. Krauss ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Thermal Emission ◽  
Light Curves ◽  
Optical Parameters ◽  
Synchrotron Emission ◽  
High Brightness ◽  
Classical Novae ◽  
Optical Light Curve ◽  
Symbiotic Binaries ◽  
Machine Readable

Abstract We present radio observations (1–40 GHz) for 36 classical novae, representing data from over five decades compiled from the literature, telescope archives, and our own programs. Our targets display a striking diversity in their optical parameters (e.g., spanning optical fading timescales, t 2 = 1–263 days), and we find a similar diversity in the radio light curves. Using a brightness temperature analysis, we find that radio emission from novae is a mixture of thermal and synchrotron emission, with nonthermal emission observed at earlier times. We identify high brightness temperature emission (T B > 5 × 104 K) as an indication of synchrotron emission in at least nine (25%) of the novae. We find a class of synchrotron-dominated novae with mildly evolved companions, exemplified by V5589 Sgr and V392 Per, that appear to be a bridge between classical novae with dwarf companions and symbiotic binaries with giant companions. Four of the novae in our sample have two distinct radio maxima (the first dominated by synchrotron and the later by thermal emission), and in four cases the early synchrotron peak is temporally coincident with a dramatic dip in the optical light curve, hinting at a common site for particle acceleration and dust formation. We publish the light curves in a machine-readable table and encourage the use of these data by the broader community in multiwavelength studies and modeling efforts.

scholarly journals An Update on Radio Supernovae

1998 ◽  
Vol 164 ◽  
pp. 357-358 ◽  
Author(s):  
Schuyler D. Van Dyk ◽  
Richard A. Sramek ◽  
Kurt W. Weiler ◽  
Marcos J. Montes ◽  
Nino Panagia
Keyword(s):  
Synchrotron Radiation ◽  
Radio Emission ◽  
Brightness Temperature ◽  
Power Law ◽  
Progress Report ◽  
Light Curves ◽  
High Brightness ◽  
Turn On ◽  
Distance Indicators ◽  
Circumstellar Environment

AbstractThe radio emission from supernovae (SNe) is nonthermal synchrotron radiation of high brightness temperature, with a “turn-on” delay at longer wavelengths, power-law decline after maximum with index β, and spectral index α asymptotically decreasing with time to a final, optically thin value. Radio supernovae (RSNe) are best described by the Chevalier (1982) “mini-shell” model, with modifications by Weiler et al. (1990). RSNe observations provide a valuable probe of the SN circumstellar environment and constraints on progenitor masses. We present a progress report on a number of recent RSNe, as well as on new behavior from RSNe 1979C and 1980K, and on RSNe as potential distance indicators. In particular, we present updated radio light curves for SN 1993J in M81.

scholarly journals Radio light curves and imaging of the helium nova V445 Puppis reveal seven years of synchrotron emission

2020 ◽  
Vol 501 (1) ◽  
pp. 1394-1412
Author(s):  
M M Nyamai ◽  
L Chomiuk ◽  
V A R M Ribeiro ◽  
P A Woudt ◽  
J Strader ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Light Curve ◽  
White Dwarf ◽  
Light Curves ◽  
Synchrotron Emission ◽  
Large Array ◽  
Very Large Array ◽  
Classical Novae ◽  
Near Ir ◽  
The Individual

ABSTRACT V445 Puppis is the only helium nova observed to date; its eruption in late 2000 showed high velocities up to 8500 km s−1, and a remarkable bipolar morphology cinched by an equatorial dust disc. Here we present multifrequency radio observations of V445 Pup obtained with the Very Large Array (VLA) spanning 1.5–43.3 GHz, and between 2001 January and 2008 March (days ∼89–2700 after eruption). The radio light curve is dominated by synchrotron emission over these 7 yr, and shows four distinct radio flares. Resolved radio images obtained in the VLA’s A configuration show that the synchrotron emission hugs the equatorial disc, and comparisons to near-IR images of the nova clearly demonstrate that it is the densest ejecta – not the fastest ejecta – that are the sites of the synchrotron emission in V445 Pup. The data are consistent with a model where the synchrotron emission is produced by a wind from the white dwarf impacting the dense equatorial disc, resulting in shocks and particle acceleration. The individual synchrotron flares may be associated with density enhancements in the equatorial disc and/or velocity variations in the wind from the white dwarf. This overall scenario is similar to a common picture of shock production in hydrogen-rich classical novae, but V445 Pup is remarkable in that these shocks persist for almost a decade, much longer than the weeks or months for which shocks are typically observed in classical novae.

Absorption in Radio Sources of High Brightness Temperature

Nature ◽  
1963 ◽  
Vol 200 (4901) ◽  
pp. 56-57 ◽  
Author(s):  
P. J. S. WILLIAMS
Keyword(s):  
Brightness Temperature ◽  
Radio Sources ◽  
High Brightness

A Gyro-Synchrotron Maser in the Solar Corona?

1978 ◽  
Vol 3 (3) ◽  
pp. 231-233 ◽  
Author(s):  
D. B. Melrose ◽  
S. M. White
Keyword(s):  
Synchrotron Radiation ◽  
Solar Corona ◽  
Brightness Temperature ◽  
Early Phase ◽  
Relativistic Electrons ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Type Iv ◽  
Alternative Suggestion ◽  
Lower Frequencies

Stewart (1978) has reported four moving type IV bursts observed with the Culgoora radio heliograph at 43, 80 and 160 MHz. After an early phase, the brightness temperatures of the observed bursts decreased with increasing frequency and with time. The highest brightness temperature observed at 43 MHz was 1010K, and it seems that the brightness temperature would have been still higher at even lower frequencies. Existing theoretical ideas on moving type IV bursts are based on data (at 80 MHz primarily) which included no brightness temperatures in excess of 109K. the accepted interpretation involved gyro-synchrotron radiation from mildly relativistic electrons (energies ≈ 100 keV); reabsorption by the electrons themselves restricts the brightness temperature to less than about 100 keV ≈ 109K (Wild and Smerd 1972, Dulk 1973). Stewart’s (1978) new data at 43 MHz require that this accepted interpretation be modified; he has suggested that higher energy electrons are involved. An alternative suggestion is explored here, namely that the absorption might be negative. In other words, the high brightness temperatures observed could be due to a gyro-synchrotron maser involving electrons with energies of about 100 keV.

scholarly journals Near-Eddington Luminosity Flares from Quiescent Supermassive Black Holes

2009 ◽  
Vol 5 (S267) ◽  
pp. 319-324
Author(s):  
Suvi Gezari
Keyword(s):  
Black Hole ◽  
Thermal Emission ◽  
Rare Event ◽  
Light Curves ◽  
Spectral Energy ◽  
Wide Field ◽  
Tidal Disruption ◽  
X Ray ◽  
Solar Type ◽  
Detection Capabilities

AbstractA dormant supermassive black hole lurking in the center of a galaxy will be revealed when a star passes within its tidal disruption radius, is disrupted, and a flare of electromagnetic radiation is emitted when the bound stellar debris is accreted. Although the tidal disruption of a star is a rare event in a galaxy, ~ 10−4 yr−1, observational candidates have emerged in all-sky X-ray and deep UV surveys in the form of luminous UV/X-ray flares from otherwise quiescent galaxies. We present the light curves and broadband properties of three tidal disruption candidates discovered in the UV by GALEX, and find that (1) the light curves are well-fitted by the power-law decline expected for the fallback of debris from a tidally disrupted solar-type star, and (2) the UV/optical spectral energy distributions can be attributed to thermal emission from an envelope of debris located at ten times the tidal disruption radius of the central black hole. We use the observed peak absolute optical magnitudes of the flares to predict the detection capabilities of the next generation of wide-field optical synoptic surveys.

scholarly journals Radio variability of blazars

2010 ◽  
Vol 6 (S275) ◽  
pp. 164-167
Author(s):  
J. H. Fan ◽  
W. Xu ◽  
J. Pan ◽  
Y. H. Yuan
Keyword(s):  
Brightness Temperature ◽  
Data Base ◽  
Preliminary Data ◽  
Light Curves ◽  
Spectrum Radio ◽  
Variability Index ◽  
Doppler Factor ◽  
Bl Lacs

AbstractIn this work, we present the analysis results using UMRAO preliminary data base. We used the light curves 1) to get the shortest timescales and then to get the brightness temperature so that we can estimate the Doppler factors; 2) to investigate the periodicity and discuss the variability index. We also used the data base to discuss the polarization properties of blazars. We found that the periodicity distribution in BL Lacs and that in the flat spectrum radio quasars should be from the same distribution. The Doppler factor in FSRQs is higher than that in BL. The polarization in BLs are higher than that in the flat spectrum radio quasars

scholarly journals The high brightness temperature of B0529+483 revealed by RadioAstron and implications for interstellar scattering

2017 ◽  
Vol 474 (3) ◽  
pp. 3523-3534 ◽  
Author(s):  
S V Pilipenko ◽  
Y Y Kovalev ◽  
A S Andrianov ◽  
U Bach ◽  
S Buttaccio ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
High Brightness ◽  
Interstellar Scattering

scholarly journals Cosmic rays and non-thermal emission in simulated galaxies: III. probing cosmic ray calorimetry with radio spectra and the FIR-radio correlation

2021 ◽  
Author(s):  
Maria Werhahn ◽  
Christoph Pfrommer ◽  
Philipp Girichidis
Keyword(s):  
Steady State ◽  
Star Formation ◽  
Thermal Emission ◽  
High Redshift ◽  
Formation Rate ◽  
Cosmic Ray ◽  
Far Infrared ◽  
Secondary Emission ◽  
Synchrotron Emission ◽  
Halo Masses

Abstract An extinction-free estimator of the star-formation rate (SFR) of galaxies is critical for understanding the high-redshift universe. To this end, the nearly linear, tight correlation of far-infrared (FIR) and radio luminosity of star-forming galaxies is widely used. While the FIR is linked to massive star formation, which also generates shock-accelerated cosmic ray (CR) electrons and radio synchrotron emission, a detailed understanding of the underlying physics is still lacking. Hence, we perform three-dimensional magneto-hydrodynamical (MHD) simulations of isolated galaxies over a broad range of halo masses and SFRs using the moving-mesh code Arepo, and evolve the CR proton energy density self-consistently. In post-processing, we calculate the steady-state spectra of primary, shock-accelerated and secondary CR electrons, which result from hadronic CR proton interactions with the interstellar medium. The resulting total radio luminosities correlate with the FIR luminosities as observed and are dominated by primary CR electrons if we account for anisotropic CR diffusion. The increasing contribution of secondary emission up to 30 per cent in starbursts is compensated by the larger bremsstrahlung and Coulomb losses. CR electrons are in the calorimetric limit and lose most of their energy through inverse Compton interactions with star-light and cosmic microwave background (CMB) photons while less energy is converted to synchrotron emission. This implies steep steady-state synchrotron spectra in starbursts. Interestingly, we find that thermal free–free emission flattens the total radio spectra at high radio frequencies and reconciles calorimetric theory with observations while free–free absorption explains the observed low-frequency flattening towards the central regions of starbursts.

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