The radio remnant of SN1993J: an instrumental explanation for the evolving complex structure

We present simulated images of Supernova 1993J at 8.4 GHz using Very Long Baseline Interferometry (VLBI) techniques. A spherically symmetric source model is convolved with realistic uv-plane distributions, together with standard imaging procedures, to assess the extent of instrumental effects on the recovered brightness distribution. In order to facilitate direct comparisons between the simulations and published VLBI images of SN1993J, the observed uv-coverage is determined from actual VLBI observations made in the years following its discovery. The underlying source model only exhibits radial variation in its density profile, with no azimuthal dependence and, even though this model is morphologically simple, the simulated VLBI observations qualitatively reproduce many of the azimuthal features of the reported VLBI observations, such as appearance and evolution of complex azimuthal structure and apparent rotation of the shell. We demonstrate that such features are inexorably coupled to the uv-plane sampling. The brightness contrast between the peaks and the surrounding shell material are not as prominent in the simulations (which of course assume no antenna- or baseline-based amplitude or phase errors, meaning no self-calibration procedures will have incorporated any such features in models). It is conclusive that incomplete uv-plane sampling has a drastic effect on the final images for observations of this nature. Difference imaging reveals residual emission up to the 8 sigma level. Extreme care should be taken when using interferometric observations to directly infer the structure of objects such as supernovae.Comment: 14 pages, 10 figures, 2 tables, accepted for publication in MNRA

A population of high-redshift type-2 quasars-II. Radio Properties

We present multi-frequency radio observations of a sample of z~2 obscured (type-2) quasars in the Spitzer extragalactic First Look Survey area. We combine the public data at 1.4 GHz, used in the selection of these sources, with new observations at 610 MHz (GMRT) and at 4.9 GHz (VLA). We find the sample includes sources with steep, flat and gigahertz-peaked spectra. There are no strong correlations between the presence or absence of emission lines in the optical spectra and the radio spectral properties of the sample. However, there are no secure flat-spectrum type-2 quasars with narrow emission lines which would be problematic for unified schemes. Most of the population have straight radio spectra with spectral index alpha~1 as is expected for developed, potentially FRI-like, jets in which continous injection of relativistic electrons is accompanied by inverse-Compton losses against the cosmic microwave background.Comment: 6 pages, 2 colour figures, submitted to MNRA

CMB foreground measurements through broad-band radio spectro-polarimetry: prospects of the SKA-MPG telescope

Basu A, Schwarz D, Kloeckner H-R, et al. CMB foreground measurements through broad-band radio spectro-polarimetry: prospects of the SKA-MPG telescope. Monthly Notices of the Royal Astronomical Society. 2019;488(2):1618-1634.Precise measurement of the foreground synchrotron emission, which contaminates the faint polarized cosmic microwave background (CMB) radiation, is a major challenge for the next-generation of CMB experiments. To address this, dedicated foreground measurement experiments are being undertaken at radio frequencies between 2 and 40 GHz. Foreground polarized synchrotron emission measurements are particularly challenging, primarily due to the complicated frequency dependence in the presence of Faraday rotation, and are best recovered through broad fractional-bandwidth polarization measurements at frequencies less than or similar to 5 GHz. A unique opportunity for measuring the foreground polarized synchrotron emission will be provided by the 15 m SKA-MPG telescope operating in the frequency range 1.7-3.5 GHz (S band). Here, we present the scope of a Southern-sky survey in S band at 1 deg angular resolution and explore its added advantage for application of powerful techniques, such as, Stokes Q, U fitting and RM-synthesis. A full Southern-sky polarization survey with this telescope, when combined with other on-going efforts at slightly higher frequencies, will provide an excellent frequency coverage for modelling and extrapolating the foreground polarized synchrotron emission to CMB frequencies (greater than or similar to 80 GHz) with rms brightness temperature better than 10 nK per 1 deg(2). We find that this survey will be crucial for understanding the effects of Faraday depolarization, especially in low Galactic latitude regions. This will allow better foreground cleaning and thus will contribute significantly in further improving component separation analyses and increase usable sky area for cosmological analysis of the Planck data, and the LiteBIRD mission in the future

Emergence of a new H I 21-cm absorption component at z 1.1726 towards the γ -ray blazar PKS 2355-106

International audienceWe report the emergence of a new H I 21-cm absorption at zabs= 1.172635 in the damped Lyα absorber (DLA) towards the γ-ray blazar PKS 2355-106 (zem~1.639) using science verification observations (June 2020) from the MeerKAT Absorption Line Survey (MALS). Since 2006, this DLA is known to show a narrow H I 21-cm absorption at zabs= 1.173019 coinciding with a distinct metal absorption line component. We do not detect significant H I 21-cm optical depth variations from this known H I component. A high resolution optical spectrum (August 2010) shows a distinct Mg I absorption at the redshift of the new H I 21-cm absorber. However, this component is not evident in the profiles of singly ionized species. We measure the metallicity ([Zn/H] = -(0.77 ±0.11) and [Si/H]= -(0.96 ±0.11)) and depletion ([Fe/Zn] = -(0.63 ±0.16)) for the full system. Using the apparent column density profiles of Si II, Fe II and Mg I we show that the depletion and the N(Mg I)/N(Si II) column density ratio systematically vary across the velocity range. The region with high depletion tends to have slightly larger N(Mg I)/N(Si II) ratio. The two H I 21-cm absorbers belong to this velocity range. The emergence of zabs= 1.172635 can be understood if there is a large optical depth gradient over a length scale of ~0.35 pc. However, the gas producing the zabs= 1.173019 component must be nearly uniform over the same scale. Systematic uncertainties introduced by the absorption line variability has to be accounted for in experiments measuring the variations of fundamental constants and cosmic acceleration even when the radio emission is apparently compact as in PKS 2355-106

Reionization and the Cosmic Dawn with the Square Kilometre Array

The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21cm line from the earliest phases of star and galaxy formation in the Universe. This 21cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescop