Clusters of galaxies : observational properties of the diffuse radio emission

Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures...(abridged)... Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.Comment: Accepted for the publication in The Astronomy and Astrophysics Review. 58 pages, 26 figure

Non-thermal X-rays from colliding wind shock acceleration in the massive binary Eta Carinae

Cosmic-ray acceleration has been a long-standing mystery1,2 and, despite more than a century of study, we still do not have a complete census of acceleration mechanisms. The collision of strong stellar winds in massive binary systems creates powerful shocks that have been expected to produce high-energy cosmic rays through Fermi acceleration at the shock interface. The accelerated particles should collide with stellar photons or ambient material, producing non-thermal emission observable in X-rays and γ-rays3,4. The supermassive binary star Eta Carinae (η Car) drives the strongest colliding wind shock in the solar neighbourhood5,6. Observations with non-focusing high-energy observatories indicate a high-energy source near η Car, but have been unable to conclusively identify η Car as the source because of their relatively poor angular resolution7,8,9. Here we present direct focussing observations of the non-thermal source in the extremely hard X-ray band, which is found to be spatially coincident with the star within several arc-seconds. These observations show that the source of non-thermal X-rays varies with the orbital phase of the binary, and that the photon index of the emission is similar to that derived through analysis of the γ-ray spectrum. This is conclusive evidence that the high-energy emission indeed originates from non-thermal particles accelerated at colliding wind shocks

Young Black Hole and Neutron Star Systems in the Nearby Star-forming Galaxy M33: The NuSTAR View

Abstract We can learn about the formation and evolution of compact objects, such as neutron stars and black holes (BHs), by studying the X-ray emission from accreting systems in nearby star-forming galaxies. The hard (E &gt; 10 keV) X-ray emission in particular allows strong discrimination among the accretion states and compact object types. We conducted a NuSTAR survey (∼600 ks) of the Local Group spiral galaxy M33 to study the distribution of X-ray binary (XRB) accretors in an actively star-forming environment. We constructed color–intensity and color–color diagrams to infer XRB accretion states. Using these diagrams, we have classified 28 X-ray sources in M33 by comparing their hard X-ray colors to those of known systems. Four sources lie in the parameter space occupied by X-ray pulsars, while 8, 10, and 4 sources lie in the parameter space occupied by BHs in the hard, intermediate, and soft states, respectively. The known ultraluminous X-ray source M33 X-8 is also found to be consistent with that source type. Some sources overlap within the Z/Atoll sources due to the overlap of the two categories of BHs and Z/Atoll sources. In contrast to a similar NuSTAR survey of M31 (with a low-mass XRB-dominant population), the source population in M33 is dominated by high-mass XRBs (HMXBs), allowing the study of a very different population with similar sensitivity due to the galaxy's similar distance. This characterization of a population of HMXB accretion states will provide valuable constraints for theoretical XRB population synthesis studies to their formation and evolution.</jats:p

Tularemia as a waterborne disease: a review

International audienceFrancisella tularensis is a Gram-negative, intracellular bacterium causing the zoonosis tularemia. This highly infectious microorganism is considered a potential biological threat agent. Humans are usually infected through direct contact with the animal reservoir and tick bites. However, tularemia cases also occur after contact with a contaminated hydrotelluric environment. Water-borne tularemia outbreaks and sporadic cases have occurred worldwide in the last decades, with specific clinical and epidemiological traits. These infections represent a major public health and military challenge. Human contaminations have occurred through consumption or use of F. tularensis-contaminated water, and various aquatic activities such as swimming, canyoning and fishing. In addition, in Sweden and Finland, mosquitoes are primary vectors of tularemia due to infection of mosquito larvae in contaminated aquatic environments. The mechanisms of F. tularensis survival in water may include the formation of biofilms, interactions with free-living amoebae, and the transition to a 'viable but nonculturable' state, but the relative contribution of these possible mechanisms remains unknown. Many new aquatic species of Francisella have been characterized in recent years. F. tularensis likely shares with these species an ability of long-term survival in the aquatic environment, which has to be considered in terms of tularemia surveillance and control