PI: Takashi Okajima, NASA Goddard Space Flight Center, Takashi.Okajima@nasa.gov
Address: Code 662, X-ray Astrophysics Laboratory, 8800 Greenbelt Rd., Greenbelt, MD 20771, USA
CoI: Tomotsugu Goto, University of Hawaii
CoI: Jack Tueller, NASA/GSFC
CoI: Richard Mushotzky, NASA/GSFC
Title: Redshift Measurement of the New Cluster of Galaxies Discovered by Swift
Abstract: We propose a redshift and velocity dispersion measurement of the new cluster of galaxies discovered by \it Swift. \it Swift/BAT hard X- ray all sky survey has been successful in detecting hard X-ray sources in the 15-200 keV band with over 270 AGNs and 7 clusters. One of the few sources without a reasonable identification is SWIFT J0356.2-3413. A 94 ks follow-up observation by the \it Swift/XRT did not detect hard point sources within the BAT error circle, however there is a clear detection of an extended source (size ~4'). It appears to be a cluster of galaxies and it has an asymmetrical structure with a gas temperature of ~8 keV and a 2-10 keV flux of 4\times 10^-13 ergs/sec/cm^2. The hard X-ray emission detected by BAT exceeds this thermal emission which makes this source very important, since an origin of hard X-ray excess emission from galaxy clusters is unclear. The X- ray image indicates a cluster merging. If the redshift z=0.37+/-0.04 derived from an iron line fitting (2\sigma detection), the temperature is too high to be on the known X-ray L-T relation. However the derived X-ray temperature could be wrong due to the possible cluster merging, which mimics higher gas temperature. We propose to eliminate this ambiguity by measuring (1) the precise redshift and (2) velocity dispersion to find the cluster merging in the new cluster of galaxies.
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