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Creators/Authors contains: "Venturi, Tiziana"

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  1. ABSTRACT We present the results of deep Chandra and XMM–Newton observations of a complex merging galaxy cluster Abell 2256 (A2256) that hosts a spectacular radio relic (RR). The temperature and metallicity maps show clear evidence of a merger between the western subcluster (SC) and the primary cluster (PC). We detect five X-ray surface brightness edges. Three of them near the cluster centre are cold fronts (CFs): CF1 is associated with the infalling SC; CF2 is located in the east of the PC; and CF3 is located to the west of the PC core. The other two edges at cluster outskirts are shock fronts (SFs): SF1 near the RR in the NW has Mach numbers derived from the temperature and the density jumps, respectively, of MT = 1.62 ± 0.12 and Mρ = 1.23 ± 0.06; SF2 in the SE has MT = 1.54 ± 0.05 and Mρ = 1.16 ± 0.13. In the region of the RR, there is no evidence for the correlation between X-ray and radio substructures, from which we estimate an upper limit for the inverse-Compton emission, and therefore set a lower limit on the magnetic field (∼ 450 kpc from PC centre) of B > 1.0 μG for a single power-law electron spectrum or B > 0.4 μG for a brokenmore »power-law electron spectrum. We propose a merger scenario including a PC, an SC, and a group. Our merger scenario accounts for the X-ray edges, diffuse radio features, and galaxy kinematics, as well as projection effects.« less
  2. Abstract We have found a class of circular radio objects in the Evolutionary Map of the Universe Pilot Survey, using the Australian Square Kilometre Array Pathfinder telescope. The objects appear in radio images as circular edge-brightened discs, about one arcmin diameter, that are unlike other objects previously reported in the literature. We explore several possible mechanisms that might cause these objects, but none seems to be a compelling explanation.