We determine the luminosity function (LF) of galaxies in the core of the Coma cluster for M R ≤ −11.4 (assuming H 0 = 75 km s −1 Mpc −1 ), a magnitude regime previously explored only in the Local Group. Objects are counted in a deep CCD image of Coma having RMS noise of 27.7 R mag arcsec −2 . A correction for objects in the foreground or background of the Coma cluster-and the uncertainty in this correction-are determined from images of five other 1 Visiting Astronomer, Kitt Peak National Observatory

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We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 sq.deg and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on-going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identified thirty-seven clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696

Theory suggests that a star making a close passage by a supermassive black hole at the center of a galaxy can under most circumstances be expected to emit a giant flare of radiation as it is disrupted and a portion of the resulting stream of shock-heated stellar debris falls back onto the black hole itself. We examine the first results of an ongoing archival survey of galaxy clusters using Chandra and XMM-Newton-selected data, and report a likely tidal disruption flare from SDSS J131122.15-012345.6 in Abell 1689. The flare is observed to vary by a factor of 30 over at least 2 years, to have maximum L X (0.3 − 3.0 keV) 5 × 10 42 erg s −1 and to emit as a blackbody with kT ∼ 0.12 keV. From the galaxy population as determined by existing studies of the cluster, we estimate a tidal disruption rate of 1.2 × 10 −4 galaxy −1 year −1 if we assume a contribution to the observable rate from galaxies whose range of luminosities corresponds to a central black hole mass (M • ) between 10 6 and 10 8 M ⊙ .We reprocessed the ACIS event files using CIAO to remove pixel randomization. According to standard CIAO data processing threads, we also applied TGAIN and CTI

Context. Due to observational constraints, dark matter determinations in nearby clusters based on weak lensing are still extremely rare, in spite of their importance for the determination of cluster properties independent of other methods. Aims. We present a weak lensing study of the Coma cluster (redshift ∼0.024) based on deep images obtained at the CFHT. Methods. After obtaining photometric redshifts for the galaxies in our field based on deep images in the u * (1 × 1 deg 2 ), and in the B, V, R and I bands (42 × 52 ), allowing us to eliminate foreground galaxies, we apply weak lensing calculations on shape measurements performed in the u * image.