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R. P. Kraft, N. Laslo, W. R. Forman, S. S. Murray, C. Jones, M. Markevitch, A. Vikhlinin (Harvard/Smithsonian CfA), E. Churazov (MPI für Astrophysik)
We present preliminary results from a 45 ks Chandra/ACIS-I observation of the nearby (z=0.01646) NGC 507 group. The surface brightness profile of the outer region of the group is well described by an isothermal \beta-profile (kBT=1.5 keV, \beta=0.345) consistent with earlier ROSAT observations. We find a sharp discontinuity in the radial surface brightness profile 55 kpc from NGC 507 covering a 100\circ arc to the E and SE. Across the edge, the surface brightness declines by a factor of 2 over a distance of 6.9 kpc (~15''). Similar features have been seen in several Chandra observations of clusters of galaxies, and are commonly believed to be evidence of the infall of sub-clusters or of gas 'sloshing' in the gravitating dark matter potential. Unlike other well-studied cold fronts, the temperature difference across the surface brightness discontinuity is small. The inner and outer gas temperatures differ by only about 0.2 keV (interior and exterior gas temperatures are 1.3 and 1.5 keV, respectively). We consider several possibilities for the origin of this unusual surface brightness discontinuity. This work was supported by NASA contracts NAS8-38248 and NAS8-39073.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.