Non-Thermal Emission from Radio-Loud AGN Jets: Radio vs. X-rays

We consider the sample of 55 blazars and Seyferts cross-correlated from the Planck all-sky survey based on the Early Release Compact Source Catalog (ERCSC) and Swift BAT 105-Month Hard X-ray Survey. The radio Planck spectra vs. X-ray Swift/XRT+BAT spectra of the active galactic nuclei (AGN) sample were fitted with the simple and broken power law (for the X-ray spectra taking into account also the Galactic neutral absorption) to test the dependencies between the photon indices of synchrotron emission (in radio range) and synchrotron self-Compton (SSC) or inverse-Compton emission (in X-rays). We show that for the major part of the AGN in our sample there is a correspondence between synchrotron and SSC photon indices (one of two for broken power-law model) compatible within the error levels. For such objects, this can give a good perspective for the task of distinguishing between the jet base counterpart from that one emitted in the disk-corona AGN “central engine”.

Outbursts of Comet 67P/Churyumov-Gerasimenko

We monitored the comet 67P/Churyumov-Gerasimenko close to its perihelion in November 2021 with the GROWTH-India Telescope. We observed two outbursts of this comet on 2021 October 29.940 and November 17.864 UTC, −3.12 days and +15.81 days respectively from the perihelion date. The brightening in the first outburst appears as a compact source, with a radial extent up to 8.″5. The comet brightened by 0.26 ± 0.03 mag in the outburst, with a 27% increase in the effective geometric cross-section and total outburst dust mass of ∼5.3 × 105 kg. The second outburst caused a brightening of 0.49 ± 0.08 mag with effective geometric cross-section and total outburst dust mass 2.5 times larger than the first event. These outbursts are up to an order of magnitude larger than the strongest outburst event observed in situ by the Rosetta spacecraft in 2015.

Gravitational waves

The theory of weak gravitational waves is discussed at length. The transverse traceless gauge is described, and the behaviour of plane wave solutions obtained. The impact of a wave on physical objects, and hence methods for their detection, are calculated. The laser interferometric gravitational wave detector is described. Sources such as binary stars are considered. The compact source approximation is employed, and the quadrupole formula relating the wave amplitude to the quadrupole of the source is obtained. Energy flux in gravitational waves is calculated by two methods, one more general, the other giving further physical insight. The total emitted power is obtained. These are lengthy calculations but they are presented in full. Finally they are applied in detail to a binary star with elliptical orbtis (the Hulse Taylor binary) and to a black hole merger detected by the LIGO interferometers.

Observations of compact sources in galaxy clusters using MUSTANG2

Compact sources can cause scatter in the scaling relationships between the amplitude of the thermal Sunyaev-Zel’dovich Effect (tSZE) in galaxy clusters and cluster mass. Estimates of the importance of this scatter vary – largely due to limited data on sources in clusters at the frequencies at which tSZE cluster surveys operate. In this paper we present 90 GHz compact source measurements from a sample of 30 clusters observed using the MUSTANG2 instrument on the Green Bank Telescope. We present simulations of how a source’s flux density, spectral index, and angular separation from the cluster’s center affect the measured tSZE in clusters detected by the Atacama Cosmology Telescope (ACT). By comparing the MUSTANG2 measurements with these simulations we calibrate an empirical relationship between 1.4 GHz flux densities from radio surveys and source contamination in ACT tSZE measurements. We find 3 per cent of the ACT clusters have more than a 20 per cent decrease in Compton-y but another 3 per cent have a 10 per cent increase in the Compton-y due to the matched filters used to find clusters. As sources affect the measured tSZE signal and hence the likelihood that a cluster will be detected, testing the level of source contamination in the tSZE signal using a tSZE selected catalog is inherently biased. We confirm this by comparing the ACT tSZE catalog with optically and X-ray selected cluster catalogs. There is a strong case for a large, high resolution survey of clusters to better characterize their source population.

Limits on long-timescale radio transients at 150 MHz using the TGSS ADR1 and LoTSS DR2 catalogues

We present a search for transient radio sources on timescales of 2-9 years at 150 MHz. This search is conducted by comparing the first Alternative Data Release of the TIFR GMRT Sky Survey (TGSS ADR1) and the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2). The overlapping survey area covers 5570 $\rm {deg}^2$ on the sky, or 14 per cent of the total sky. We introduce a method to compare the source catalogues that involves a pair match of sources, a flux density cutoff to meet the survey completeness limit and a newly developed compactness criterion. This method is used to identify both transient candidates in the TGSS source catalogue that have no counterpart in the LoTSS catalogue and transient candidates in LoTSS without a counterpart in TGSS. We find that imaging artefacts and uncertainties and variations in the flux density scales complicate the transient search. Our method to search for transients by comparing two different surveys, while taking into account imaging artefacts around bright sources and misaligned flux scales between surveys, is universally applicable to future radio transient searches. No transient sources were identified, but we are able to place an upper limit on the transient surface density of <5.4 · 10−4 deg−2 at 150 MHz for compact sources with an integrated flux density over 100 mJy. Here we define a transient as a compact source with flux density greater than 100 mJy that appears in the catalogue of one survey without a counterpart in the other survey.

Efficient Holographic Focusing Metasurface

We present the design and experimental demonstration of an efficient holographic metasurface aperture that focuses microwaves in the Fresnel zone. The proposed circular structure consists of two stacked plates with their periphery terminated in a conductive layer. Microwaves are injected into the bottom plate, which forms the feed layer, and are coupled to the top holographic metasurface layer via an annular ring. This coupling results in an inward traveling cylindrical wave in the top layer, which serves as the reference wave for a hologram. The radiating elements consist of a slot pair with their orientations designed to couple efficiently with the cylindrical reference wave while maintaining a linearly polarized focused beam. A general condition on the slot pairs radiated power is proposed to ensure low sidelobe level (SLL) and is validated with full-wave simulation. An aperture that is 20 cm in diameter, operates at 20 GHz in the K-band frequency, and forms a diffraction-limited focal spot at a distance of 10 cm is experimentally demonstrated. The proposed near-field focusing metasurface has high antenna efficiency and can find application as a compact source for Fresnel-zone wireless power transfer and remote sensing schemes.