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Author: search.filters.author.Bagchi, JoydeepSubject: search.filters.subject.Clusters

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    BeppoSAX observation of the rich cluster of galaxies Abell 85
    (2001-01-06) Lima Neto, G. B.; Pislar, V.; Bagchi, Joydeep
    We report the observation of the Intra-Cluster Medium (ICM) of Abell 85 by the X-ray satellite Bep- poSAX. We have both analysed the spectrum obtained in the central 8 arcmin circular region centred on the Very Steep Spectrum Radio Source (VSSRS) and the spec- tra from a number of sub-regions. Analysis of the spec- tra allowed us to independently obtain new estimates of the temperature, metallicity and line-of-sight hydro- gen density column, both globally (T = 6.6 ± 0.3 keV, Z = 0.38 ± 0.06Z⊙ and NH = 5.5+0.9 −0.71020cm−2) and lo- cally. These measures are in good agreement with previ- ous measures based on ROSAT and ASCA data. In the region of the VSRSS, we have tried to disentangle the thermal from the non-thermal X-ray emission. Although we could not do this unambiguously, we have nonethe- less estimated the extended magnetic field using the radio spectrum available for this region.We obtain a lower limit intensity of 0.9µG, consistent with our previous estimate. We also derive α-elements/iron abundance ratios that turn out to be higher than 1. Such a result tends to support the burst model for elliptical galaxies, where a strong galac- tic wind develops early in the galaxy history and type II supernovae (SN) may have the main role in the enrich- ment of the ICM. A two-temperature ICM model was fit- ted in the central region yielding a main component with roughly the mean cluster temperature and a cooler com- ponent with temperature less than 0.1 keV.
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    Radio observations of ZwCl 2341.1+0000: a double radio relic cluster
    (2009-10-01) Weeren, R.; Miniati, F.; Bagchi, Joydeep; et al.
    infall and mergers of smaller subclusters and galaxy groups. Diffuse radio emission, in the form of radio halos and relics, is found in clusters undergoing a merger, indicating that shocks or turbulence associated with the merger are capable of accelerating electrons to highly relativistic energies. Double relics are a rare class of radio sources found in the periphery of clusters, with the two components located symmetrically on the opposite sides of the cluster center. These relics are important probes of the cluster periphery as (i) they provide an estimate of the magnetic field strength, and (ii) together with detailed modeling can be used to derive information about the merger geometry, mass, and timescale. Observations of these double relics can thus be used to test the framework of LSS formation. Here we report on radio observations of ZwCl 2341.1+0000, a complex merging structure of galaxies located at z = 0.27, using Giant Metrewave Radio Telescope (GMRT) observations. Aims. The main aim of the observations is to study the nature of the diffuse radio emission in the galaxy cluster ZwCl 2341.1+0000. Methods. We carried out GMRT 610, 241, and 157 MHz continuum observations of ZwCl 2341.1+0000. The radio observations are combined with X-ray and optical data of the cluster. Results. The GMRT observations show a double peripheral radio relic in the cluster ZwCl 2341.1+0000. The spectral index is −0.49 ± 0.18 for the northern relic and −0.76 ± 0.17 for the southern relic. We have derived values of 0.48 − 0.93 µGauss for the equipartition magnetic field strength. The relics are probably associated with outward traveling merger shock waves.