Diffuse radio emission in MACS J0025.4−-1222: the effect of a major merger on bulk separation of ICM components

Mergers of galaxy clusters are among the most energetic events in the Universe. These events have significant impact on the intra-cluster medium, depositing vast amounts of energy - often in the form of shocks - as well as heavily influencing the properties of the constituent galaxy population. Many clusters have been shown to host large-scale diffuse radio emission, known variously as radio haloes and relics. These sources arise as a result of electron (re-)acceleration in cluster-scale magnetic fields, although the processes by which this occurs are still poorly understood. We present new, deep radio observations of the high-redshift galaxy cluster MACS J0025.4$-$1222, taken with the GMRT at 325 MHz, as well as new analysis of all archival $Chandra$ X-ray observations. We aim to investigate the potential of diffuse radio emission and categorise the radio population of this cluster, which has only been covered previously by shallow radio surveys. We produce low-resolution maps of MACS J0025.4$-$1222 through a combination of uv-tapering and subtracting the compact source population. Radial surface brightness and mass profiles are derived from the $Chandra$ data. We also derive a 2D map of the ICM temperature. For the first time, two sources of diffuse radio emission are detected in MACS J0025.4$-$1222, on linear scales of several hundred kpc. Given the redshift of the cluster and the assumed cosmology, these sources appear to be consistent with established trends in power scaling relations for radio relics. The X-ray temperature map presents evidence of an asymmetric temperature profile and tentative identification of a temperature jump associated with one relic. We classify the pair of diffuse radio sources in this cluster as a pair of radio relics, given their consistency with scaling relations, location toward the cluster outskirts, and the available X-ray data.Comment: 20 pages, 15 figures, accepted for publication in A&

Early Science with the Karoo Array Telescope: a Mini-Halo Candidate in Galaxy Cluster Abell 3667

Abell 3667 is among the most well-studied galaxy clusters in the Southern Hemisphere. It is known to host two giant radio relics and a head-tail radio galaxy as the brightest cluster galaxy. Recent work has suggested the additional presence of a bridge of diffuse synchrotron emission connecting the North-Western radio relic with the cluster centre. In this work, we present full-polarization observations of Abell 3667 conducted with the Karoo Array Telescope at 1.33 and 1.82 GHz. Our results show both radio relics as well as the brightest cluster galaxy. We use ancillary higher-resolution data to subtract the emission from this galaxy, revealing a localised excess, which we tentatively identify as a radio mini-halo. This mini-halo candidate has an integrated flux density of $67.2\pm4.9$ mJy beam$^{-1}$ at 1.37 GHz, corresponding to a radio power of P$_{\rm{1.4\,GHz}}=4.28\pm0.31\times10^{23}$ W Hz$^{-1}$, consistent with established trends in mini-halo power scaling.Comment: 17 pages, 10 figures, accepted MNRA

Magnetic relaxation of a system of superparamagnetic particles weakly coupled by dipole-dipole interactions

The effect of long range dipole-dipole interactions on the thermal fluctuations of the magnetization of an assembly of single-domain ferromagnetic particles is considered. If orientational correlations between the particles are neglected, the evolution of the magnetization orientations may be described by a nonlinear Fokker-Planck equation (FPE) reducing to the usual linear one in the limit of infinite dilution [W.F. Brown Jr, Phys. Rev. 130, 1677 (1963)]. The thermally activated relaxation time scale of the assembly is estimated, leading to a simple modification of the axially symmetric asymptotes for the superparamagnetic relaxation time.Comment: 31 pages, 3 figures, regular articl

Optical nonlinearity enhancement of graded metallic films

The effective linear and third-order nonlinear susceptibility of graded metallic films with weak nonlinearity have been investigated. Due to the simple geometry, we were able to derive exactly the local field inside the graded structures having a Drude dielectric gradation profile. We calculated the effective linear dielectric constant and third-order nonlinear susceptibility. We investigated the surface plasmon resonant effect on the optical absorption, optical nonlinearity enhancement, and figure of merit of graded metallic films. It is found that the presence of gradation in metallic films yields a broad resonant plasmon band in the optical region, resulting in a large enhancement of the optical nonlinearity and hence a large figure of merit. We suggest experiments be done to check our theoretical predictions, because graded metallic films can be fabricated more easily than graded particles.Comment: 11 pages, 2 eps figures, submitted to Applied Physics Letter

Culture of airway epithelial cells from neonates sampled within 48-hours of birth

Peer reviewedPublisher PD

Optical nonlinearity enhancement of graded metal-dielectric composite films

We have derived the local electric field inside graded metal-dielectric composite films with weak nonlinearity analytically, which further yields the effective linear dielectric constant and third-order nonlinear susceptibility of the graded structures. As a result, the composition-dependent gradation can produce a broad resonant plasmon band in the optical region, resulting in a large enhancement of the optical nonlinearity and hence a large figure of merit.Comment: 11 pages, 2 figures. To be published in Europhysics Letter