Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 µm, 870 µm, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2 M ). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated to the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.

We present our extensive observations of the radio emission from supernova (SN) 1993J, in M 81 (NGC 3031), made with the Very Large Array, at 90, 20, 6, 3.6, 2, 1.2, and 0.7 cm, as well as numerous measurements from other telescopes and at other wavelengths. The combined data set constitutes probably the most detailed set of measurements ever established for any SN outside of the Local Group in any wavelength range. Only the very subluminous SN 1987A in the Large Magellanic Cloud has been the subject of such an intensive observational program. The radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-supernova stellar wind describes the observations rather well considering the complexity of the phenomenon. However: 1) The highest frequency measurements at 85 -110 GHz at early times (< 40 days) are not well fitted by the parameterization which describes the cm wavelength measurements rather well. 2) At mid-cm wavelengths there is often deviation from the fitted radio light curves, particularly near the peak flux density, and considerable shorter term deviations in the declining portion when the emission has become optically thin. 3) At a time ∼ 3100 days after shock breakout, the decline rate of the radio emission steepens from (t +β ) β ∼ −0.7 to β ∼ −2.7 without change in the spectral index (ν +α ; α ∼ −0.81). However, this decline is best described not as a power-law, but as an exponential decay starting at day 3100 with an e-folding time of ∼ 1100 days. 4) The best overall fit to all of the data is a model including both non-thermal synchrotron self-absorption (SSA) and a thermal free-free absorbing (FFA) components at early times, evolving to a constant spectral index, optically thin decline rate, until a break in that decline rate at day ∼ 3100 as mentioned above. Moreover, neither a purely SSA nor a purely FFA absorbing models can provide a fit that simultaneously reproduces the light curves, the spectral index evolution, and the brightness temperature evolution. 5) The radio and X-ray light curves display quite similar behavior and both suggest a sudden drop in the supernova progenitor mass-loss rate at ∼ 8000 years prior to shock breakout.

We report deep EVN and eMERLIN observations of the Type Ia SN 2014J in the nearby galaxy M 82. Our observations represent, together with JVLA observations of SNe 2011fe and 2014J, the most sensitive radio studies of Type Ia SNe ever. By combining data and a proper modeling of the radio emission, we constrain the mass-loss rate from the progenitor system of SN 2014J toṀ 7.0 × 10 −10 M yr −1 (for a wind speed of 100 km s −1 ). If the medium around the supernova is uniform, then n ISM 1.3 cm −3 , which is the most stringent limit for the (uniform) density around a Type Ia SN. Our deep upper limits favor a double-degenerate (DD) scenario-involving two WD stars-for the progenitor system of SN 2014J, as such systems have less circumstellar gas than our upper limits. By contrast, most single-degenerate (SD) scenarios, i.e., the wide family of progenitor systems where a red giant, main-sequence, or sub-giant star donates mass to a exploding WD, are ruled out by our observations a . Our estimates on the limits to the gas density surrounding SN2011fe, using the flux density limits from Chomiuk et al. (2012), agree well with their results. Although we discuss possibilities for a SD scenario to pass observational tests, as well as uncertainties in the modeling of the radio emission, the evidence from SNe 2011fe and 2014J points in the direction of a DD scenario for both. a While completing our work, we noticed that a paper by Margutti et al. (2014) was submitted to The Astrophysical Journal. From a non-detection of X-ray emission from SN 2014J, the authors obtain limits ofṀ < ∼ 1.2 × 10 −9 M yr −1 (for a wind speed of 100 km s −1 ) and n ISM < ∼ 3.5 cm −3 , for the ρ ∝ r −2 wind and constant density cases, respectively. As these limits are less constraining than ours, the findings by Margutti et al. (2014) do not alter our conclusions. The X-ray results are, however, important to rule out free-free and synchrotron self-absorption as a reason for the radio non-detections.

We present the first numerical simulations of the parsec-scale synchrotron emission from hydrodynamic relativistic jets. The jet structure is calculated using a relativistic time-dependent hydrodynamic code based on an approximate Riemann solver. The radio emission from the model jets is calculated by integrating the transfer equations of the synchrotron radiation, accounting for the appropriate opacity and relativistic effects, such as Doppler boosting and relativistic aberration. In order to study the influence of the external medium, we present two hydrodynamical jet simulations: one with a constant external pressure, and a second model with a decreasing external pressure. Multifrequency radio images of the synchrotron emission from these flows are presented, showing the existence of stationary quasi-periodic knots associated with internal oblique shocks. Whereas for the model with constant external pressure the knots remain almost constant in intensity and even in spacing, the model with decreasing external pressure shows stationary knots of progressively lower intensity and wider spacing as a function of distance down the jet.