A combined JVLA and Chandra study of the Abell 2626 galaxy cluster

In this thesis work we carried out an accurate analysis of new observations of the galaxy cluster Abell 2626 in the radio and X-ray bands. Its radio emission is characterized by the presence of a system of peculiar radio sources, the arcs , whose properties differs from the properties of the common cluster diffuse radio sources. In the past years, several models have been proposed to explain their origin. Our work aims at investigating the origin of the arcs. We analyzed new JVLA observations of the cluster at 3.0 GHz and 5.5 GHz. During the radio analysis we detected the arcs at 3.0 GHz and possible evidences for extended emission inside them at 5.5 GHz. By combining archival maps at 1.4 GHz and the new ones at 3.0 GHz, we estimated that the arcs have a spectral index α ∼ -3. The analysis of a new CHANDRA observation of the cluster produced surprising results. We highlighted the a spatial connection between the radio arcs and a cold region inside the cluster core and, moreover, we discovered a cold front which coincides with the south-west junction of the radio arcs. It is well known that the turbulence inside the cold fronts is able to accelerate the relativistic particles, triggering radio emission in form of mini-halos. Under certain conditions, this emission results in form of collimated steep-spectrum arcs that traces the dynamics of the cold fronts. So we proposed a scenario, in which the arcs are not related to the precession of AGN jets, but instead are produced by non-thermal processes (particle acceleration and magnetic fled amplification) that are related to the formation and the evolution of the cold fronts in the core of Abell 2626. In this case the peculiar morphology of the arcs is the result of the dynamics of the cold fronts, that will be studied with future MHD simulations

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New JVLA observations at 3 GHz and 5.5 GHz of the `Kite' radio source in Abell 2626

We report on new JVLA observations performed at 3 GHz and 5.5 GHz of Abell 2626. The cluster has been the object of several studies in the recent years due to its peculiar radio emission, which shows a complex system of symmetric radio arcs characterized by a steep spectrum. The origin of these radio sources is still unclear. Due to their mirror symmetry toward the center, it has been proposed that they may be created by pairs of precessing jets powered by the inner AGN. The new JVLA observations were requested with the specific aim of detecting extended emission on frequencies higher than 1.4 GHz, in order to constrain the jet-precession model by analyzing the spectral index and radiative age patterns alongs the arcs. We performed a standard data reduction of the JVLA datasets with the software CASA. By combining the new 3 GHz data with the archival 1.4 GHz VLA dataset we produced a spectral index maps of the extended emission, and then we estimated the radiative age of the arcs by assuming that the plasma was accelerated in moving hot-spots tracing the arcs. Thanks to the high sensitivity of the JVLA, we achieve the detection of the arcs at 3 GHz and extended emission at 5.5 GHz. We measure a mean spectral index <-2.5 for the arcs up to 3 GHz. No clear spectral index, or radiative age, trend is detected across the arcs which may challenge the interpretation based on precession or put strong constraints on the jet-precession period. In particular, by analyzing the radiative age distribution along the arcs, we were able to provide for the first time a time-scale < 26 Myr of the jet-precession period.Comment: 8 pages, 5 figures. Accepted for publication in A&

Dual applicator thermal ablation at 2.45 GHz: a numerical comparison and experiments on synchronous versus asynchronous and switched-mode feeding

This paper compares the results obtained with numerical simulations and ex vivo experiments involving a dual applicator microwave thermal ablation system operating at a 2.45 GHz frequency, both in synchronous and asynchronous modes. Our purpose was to demonstrate that at this frequency an asynchronous or switched-mode system performs essentially as well as the synchronous one, in spite of the prevailing belief that coherence would assure better thermal (TH) synergy. Numerical analysis: The calculations of temperature fields were based on the Pennes bioheat equation, taking into account the effects of blood perfusion by means of a full-wave 3D simulator that allows numerical electromagnetic (EM) and TH analyses.Experiments were done using a 100 W microwave (MW) power generator and a fast switched-mode sequential 'active' power splitter. By adding a further passive power splitter we arranged a test bed for an accurate experimental comparison of synchronous versus switched-mode TH ablations.The experimental ablation zones produced by a dual applicator array on ex vivo swine tissue corresponded well with the simulated ones, confirming that the simplifications assumed in the full-wave analysis were compatible with the aim of our work.Numerical simulations and experiments show that at a 2.45 GHz industrial, scientific and medical (ISM) frequency, synchronous, asynchronous and switched-mode multi-probe systems are substantially equivalent in terms of ablative performance. Moreover, the switched-mode solution offers simpler operation along with lesser sensitivity to the placement of applicators in the tissue

The mystery of the 'Kite' radio source in Abell 2626: insights from new Chandra observations

We present the results of a new Chandra study of the galaxy cluster A2626. The radio emission of the cluster shows a complex system of four symmetric arcs without known correlations with the X-ray emission. The mirror symmetry of the radio arcs toward the center and the presence of two optical cores in the central galaxy suggested that they may be created by pairs of precessing radio jets powered by dual AGNs inside the cD galaxy. However, previous observations failed to observe the second jetted AGN and the spectral trend due to radiative age along the radio arcs, thus challenging this interpretation. The new Chandra observation had several scientific objectives, including the search for the second AGN that would support the jet precession model. We focus here on the detailed study of the local properties of the thermal and non-thermal emission in the proximity of the radio arcs, in order to get more insights into their origin. We performed a standard data reduction of the Chandra dataset deriving the radial profiles of temperature, density, pressure and cooling time of the intra-cluster medium. We further analyzed the 2D distribution of the gas temperature, discovering that the south-western junction of the radio arcs surrounds the cool core of the cluster. We studied the X-ray SB and spectral profiles across the junction, finding a cold front spatially coincident with the radio arcs. This may suggest a connection between the sloshing of the thermal gas and the nature of the radio filaments, raising new scenarios for their origin. A possibility is that the radio arcs trace the projection of a complex surface connecting the sites where electrons are most efficiently reaccelerated by the turbulence that is generated by the gas sloshing. In this case, diffuse emission embedded by the arcs and with extremely steep spectrum should be most visible at very low radio frequencies.Comment: 7 pages, 7 figures. Accepted for publication on A&

Procedura per la valutazione dell'emissione di campi EM da un apparato per ipetermia con componente diatermica a 434.0 MHz e verifica del rispetto degli standard

The objective of this technical report is to establish a measurement procedure and/or measurement protocol in order to characterize the electromagnetic, electric and/or magnetic field sources at the workplaces, particularly in hospitals and in medical environmental. In this particular cases the exposure to electromagnetic fields involve workers, in-patients and their parents, and the devices and medical equipments. For the workers case we refer on the D.Lgs 81/2008 which acknowledges the European Directive 2004/40/EC on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields). For the in-patients the risk-benefit evaluation for exposure to electromagnetic fields is to advantage of benefit, except particular situations. For the parents of the in-patients we apply the standard fixed by the italian law (DPCM 8 Luglio 2003 “Fissazione dei limiti di esposizione, dei valori di attenzione e degli obiettivi di qualità per la protezione della popolazione dalle esposizioni a campi elettrici, magnetici ed elettromagnetici generati a frequenze comprese fra 100 kHz e 300 GHz”) For the devices and the medical equipments we refer to the CEI EN 60601-1-2. The standard fixes the electromagnetic immunity limits to 10 V/m for life-supporting equipments and systems and to 3 V/m for no life-supporting equipments and systems An instrument device for hyperthermia (Delta, Easytech Srl) has been chose as case-study for test the proposed measurement procedure. This instrument device is used in medical environmental to treatment of the pathologies of the locomotor apparatus. Its operating frequency is in ISM band (433.05÷434.79 MHz)

Statistical outliers in random laser emission

We provide theoretical and experimental evidence of statistical outliers in random laser emission that are not accounted for by the, now established, power-law tailed (L\'evy) distribution. Such outliers manifest themselves as single, large isolated spikes over an otherwise smooth background. A statistical test convincingly shows that their probability is larger than the one extrapolated from lower-intensity events. To compare with experimental data, we introduced the anomaly parameter that allows for an identification of such rare events from experimental spectral measurements and that agrees as well with the simulations of our Monte Carlo model. A possible interpretation in terms of Black Swans or Dragon Kings, large events having a different generation mechanism from their peers, is discussed