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.

The results of an extremely deep, 8‐d long observation of the central kpc of the nearby starburst galaxy M82 using Multi‐Element Radio Linked Interferometer Network (MERLIN) at 5 GHz are presented. The 17 μJy beam−1 rms noise level in the naturally weighted image makes it the most sensitive high‐resolution radio image of M82 made to date. Over 50 discrete sources are detected, the majority of which are supernova remnants, but with 13 identified as H ii regions. Sizes, flux densities and radio brightnesses are given for all of the detected sources, which are all well resolved with a majority showing shell or partial shell structures. Those sources within the sample which are supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size of 2.9 pc. From a comparison with previous MERLIN 5‐GHz observations made in 1992 July, which gives a 9.75‐yr timeline, it has been possible to measure the expansion velocities of 10 of the more compact sources, eight of which have not been measured before. These derived expansion velocities range between 2200 and 10 500 km s−1.

We present the first data release of high-resolution ( 0.2 arcsec) 1.5-GHz radio images of 103 nearby galaxies from the Palomar sample, observed with the eMERLIN array, as part of the LeMMINGs survey. This sample includes galaxies which are active (LINER and Seyfert) and quiescent (Hii galaxies and Absorption line galaxies, ALG), which are reclassified based upon revised emission-line diagrams. We detect radio emission 0.2 mJy for 47/103 galaxies (22/34 for LINERS, 4/4 for Seyferts, 16/51 for Hii galaxies and 5/14 for ALGs) with radio sizes typically of 100 pc. We identify the radio core position within the radio structures for 41 sources. Half of the sample shows jetted morphologies. The remaining half shows single radio cores or complex morphologies. LINERs show radio structures more core-brightened than Seyferts. Radio luminosities of the sample range from 10 32 to 10 40 erg s −1 : LINERs and Hii galaxies show the highest and the lowest radio powers respectively, while ALGs and Seyferts have intermediate luminosities.We find that radio core luminosities correlate with black hole (BH) mass down to ∼10 7 M , but a break emerges at lower masses. Using [O III] line luminosity as a proxy for the accretion luminosity, active nuclei and jetted Hii galaxies follow an optical fundamental plane of BH activity, suggesting a common disc-jet relationship. In conclusion, LINER nuclei are the scaled-down version of FR I radio galaxies; Seyferts show less collimated jets; Hii galaxies may host weak active BHs and/or nuclear starforming cores; and recurrent BH activity may account for ALG properties.

From a combination of Multi‐Element Radio‐Linked Interferometer Network (MERLIN) and global Very Long Baseline Interferometry (VLBI) observations of the starburst galaxy M82, images of 36 discrete sources at resolutions ranging from ∼3 to ∼80 mas at 1.7 GHz are presented. Of these 36 sources, 32 are identified as supernova remnants, two are H ii regions and three remain unclassified. Sizes, flux densities and radio brightnesses are given for all of the detected sources. Additionally, global VLBI only data from this project are used to image four of the most compact radio sources. These data provide a fifth epoch of VLBI observations of these sources, covering a 19‐yr time‐line. In particular, the continued expansion of one of the youngest supernova remnants, 43.31+59.3, is discussed. The deceleration parameter is a power‐law index used to represent the time evolution of the size of a supernova remnant. For the source 43.31+59.3, a lower limit to the deceleration parameter is calculated to be 0.53 ± 0.06, based on a lower limit of the age of this source.

Prior to the launch of NuSTAR, it was not feasible to spatially resolve the hard (E > 10 keV) emission from galaxies beyond the Local Group. The combined NuSTAR dataset, comprised of three ∼ 165 ks observations, allows spatial characterization of the hard X-ray emission in the galaxy NGC 253 for the first time. As a follow up to our initial study of its nuclear region, we present the first results concerning the full galaxy from simultaneous NuSTAR, Chandra, and VLBA monitoring of the local starburst galaxy NGC 253. Above ∼ 10 keV, nearly all the emission is concentrated within 100 ′′ of the galactic center, produced almost exclusively by three nuclear sources, an off-nuclear ultraluminous X-ray source (ULX), and a pulsar candidate that we identify for the first time in these observations. We detect 21 distinct sources in energy bands up to 25 keV, mostly consisting of intermediate state black hole X-ray binaries. The global X-ray emission of the galaxydominated by the off-nuclear ULX and nuclear sources, which are also likely ULXs -falls steeply (photon index ∼ > 3) above 10 keV, consistent with other NuSTAR-observed ULXs, and no significant excess above the background is detected at E > 40 keV. We report upper limits on diffuse inverse Compton emission for a range of spatial models. For the most extended morphologies considered, these hard X-ray constraints disfavor a dominant inverse Compton component to explain the γ-ray emission detected with Fermi and H.E.S.S. If NGC 253 is typical of starburst galaxies at higher redshift, their contribution to the E > 10 keV cosmic X-ray background is < 1%.

We present the results of a second epoch of 18‐cm global very long baseline interferometry (VLBI) observations, taken on 2001 February 23, of the central kiloparsec of the nearby starburst galaxy Messier 82. These observations further investigate the structural and flux evolution of the most compact radio sources in the central region of M82. The two most compact radio objects in M82 have been investigated (41.95+575 and 43.31+592). Using this recent epoch of data in comparison with our previous global VLBI observations and two earlier epochs of European VLBI network observations, we measure expansion velocities in the range of 1500–2000 km s−1 for 41.95+575 and 9000–11 000 km s−1 for 43.31+592 using various independent methods. In each case, the measured remnant expansion velocities are significantly larger than the canonical expansion velocity (500 km s−1) of supernova remnants (SNRs) within M82 predicted from theoretical models. In this paper, we discuss the implications of these measured expansion velocities with respect to the high‐density environment that the SNRs are expected to reside in within the centre of the M82 starburst.

We assemble a large set of 2–10 GHz radio flux density measurements and upper limits of 294 different supernovae (SNe), from the literature and our own and archival data. Only 31% of SNe were detected. We characterize the SN radio lightcurves near the peak using a two-parameter model, with t pk being the time to rise to a peak and L pk the spectral luminosity at that peak. Over all SNe in our sample at D < 100 Mpc, we find that t pk = 101.7±0.9 days and that L pk = 1025.5±1.6 erg s−1 Hz−1, and therefore that generally 50% of SNe will have L pk < 1025.5 erg s−1 Hz−1. These L pk values are ∼30 times lower than those for only detected SNe. Types Ib/c and II (excluding IIn’s) have similar mean values of L pk but the former have a wider range, whereas Type IIn SNe have ∼10 times higher values with L pk = 1026.5±1.1 erg s−1 Hz−1. As for t pk, Type Ib/c have t pk of only 101.1±0.5 days while Type II have t pk = 101.6±1.0 and Type IIn the longest timescales with t pk = 103.1±0.7 days. We also estimate the distribution of progenitor mass-loss rates, , and find that the mean and standard deviation of are −5.4 ± 1.2 (assuming v wind = 1000 km s−1) for Type Ib/c SNe, and −6.9 ± 1.4 (assuming v wind = 10 km s−1) for Type II SNe excluding Type IIn.

The class of type Ic supernovae have drawn increasing attention since 1998 owing to their sparse association (only four so far) with long duration gamma-ray bursts (GRBs). Although both phenomena originate from the core collapse of a massive star, supernovae emit mostly at optical wavelengths, whereas GRBs emit mostly in soft gamma-rays or hard X-rays. Though the GRB central engine generates ultra-relativistic jets, which beam the early emission into a narrow cone, no relativistic outflows have hitherto been found in type Ib/c supernovae explosions, despite theoretical expectations and searches. Here we report radio (interferometric) observations that reveal a mildly relativistic expansion in a nearby type Ic supernova, SN 2007gr. Using two observational epochs 60 days apart, we detect expansion of the source and establish a conservative lower limit for the average apparent expansion velocity of 0.6c. Independently, a second mildly relativistic supernova has been reported. Contrary to the radio data, optical observations of SN 2007gr indicate a typical type Ic supernova with ejecta velocities approximately 6,000 km s(-1), much lower than in GRB-associated supernovae. We conclude that in SN 2007gr a small fraction of the ejecta produced a low-energy mildly relativistic bipolar radio jet, while the bulk of the ejecta were slower and, as shown by optical spectropolarimetry, mildly aspherical.