VENTURI, TizianaTizianaVENTURIROSSETTI, MARIACHIARAMARIACHIARAROSSETTIBrunetti, G.G.BrunettiFarnsworth, D.D.FarnsworthGASTALDELLO, FABIOFABIOGASTALDELLOGiacintucci, S.S.GiacintucciLal, D. V.D. V.LalRudnick, L.L.RudnickShimwell, T. W.T. W.ShimwellEckert, D.D.EckertMOLENDI, SILVANOSILVANOMOLENDIOwers, M.M.Owers2020-09-142020-09-1420170004-6361http://hdl.handle.net/20.500.12386/27346Aims: We report on a spectral study at radio frequencies of the giant radio halo in A 2142 (z = 0.0909), which we performed to explore its nature and origin. The optical and X-ray properties of the cluster suggest that A 2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. Methods: We performed deep radio observations of A 2142 with the Giant Metrewave Radio Telescope (GMRT) at 608 MHz, 322 MHz, and 234 MHz and with the Very Large Array (VLA) in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions, from the galaxy scale, I.e. 5'', up to 60'' to image the diffuse cluster-scale emission. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A 2142, about 1 Mpc away from the cluster centre. We studied the spectral index in two regions: the central part of the halo, where the X-ray emission peaks and the two brightest dominant galaxies are located; and a second region, known as the ridge (in the direction of the most distant south-eastern cold front), selected to follow the bright part of the halo and X-ray emission. We complemented our deep observations with a preliminary LOw Frequency ARray (LOFAR) image at 118 MHz and with the re-analysis of archival VLA data at 1.4 GHz. <BR /> Results: The two components of the radio halo show different observational properties. The central brightest part has higher surface brightess and a spectrum whose steepness is similar to those of the known radio halos, I.e. α<SUP>1.78 GHz</SUP><SUB>118 MHz</SUB> = 1.33 ± 0.08 . The ridge, which fades into the larger scale emission, is broader in size and has considerably lower surface brightess and a moderately steeper spectrum, I.e. α<SUP>1.78 GHz</SUP><SUB>118 MHz</SUB> 1.5. We propose that the brightest part of the radio halo is powered by the central sloshing in A 2142, in a process similar to what has been suggested for mini-halos, or by secondary electrons generated by hadronic collisions in the ICM. On the other hand, the steeper ridge may probe particle re-acceleration by turbulence generated either by stirring the gas and magnetic fields on a larger scale or by less energetic mechanisms, such as continuous infall of galaxy groups or an off-axis (minor) merger.STAMPAenArticle10.1051/0004-6361/2016300142-s2.0-85025170938000406619100052https://www.aanda.org/articles/aa/abs/2017/07/aa30014-16/aa30014-16.html2017A&A...603A.125VFIS/05 - ASTRONOMIA E ASTROFISICA