RASSEBCS - ROSAT All-Sky Survey Extended Brightest Cluster Sample
The low-flux extension of the X-ray-selected ROSAT Brightest Cluster Sample was published in Ebeling et al. (2000, MNRAS, 318, 333; Paper IV). Like the original BCS and employing an identical selection procedure, the BCS extension is compiled from ROSAT All-Sky Survey (RASS) data in the northern hemisphere (Dec >=0 degrees) and at high Galactic latitudes (|b| >= 20 degrees). It comprises 99 X-ray-selected clusters of galaxies with measured redshifts z <= 0.3 (as well as eight more at z > 0.3) and total fluxes between 2.8 x 10^-12 and 4.4 x 10^-12 erg/cm^2/s in the 0.1 - 2.4keV band (the latter value being the flux limit of the original BCS). The extension can be combined (as it has been in this HEASARC table) with the main sample published in 1998 to form the homogeneously selected extended BCS (eBCS), the largest and statistically best understood cluster sample to emerge from the RASS to date. The nominal completeness of the combined sample (defined with respect to a power-law fit to the bright end of the BCS log N -log S distribution) is relatively low at 75% (compared with 90% for the high-flux sample of Paper I). However, just as for the original BCS, this incompleteness can be accurately quantified, and thus statistically corrected for, as a function of X-ray luminosity and redshift. In addition to its importance for improved statistical studies of the properties of clusters in the local Universe, the low-flux extension of the BCS is also intended to serve as a finding list for X-ray-bright clusters in the northern hemisphere which the authors hoped will prove useful in the preparation of cluster observations to be made with the next generation of X-ray telescopes such as Chandra and XMM-Newton.
The ROSAT Brightest Cluster Sample - I. The compilation of the sample and the cluster log N-log S distribution. Ebeling H., Edge A.C., Boehringer H., Allen S.W., Crawford C.S., Fabian A.C., Voges W., Huchra J.P. <Mon. Not. R. Astron. Soc. 301, 881 (1998)> =1998MNRAS.301..881E The ROSAT Brightest Cluster Sample - IV. The extended sample. Ebeling H., Edge A.C., Allen S.W., Crawford C.S., Fabian A.C., Huchra J.P. <Mon. Not. R. Astron. Soc. 318, 333 (2000)> =2000MNRAS.318..333E
The name of the cluster of galaxies, where 'A' is used for Abell (or ACO) clusters. Where clusters appear to consist of two components, two entries with 'a' and 'b' suffixes are listed. The authors have adopted cluster names in the following order of priority: Abell name, Zwicky name, another cluster name established in the literature, and ROSAT 'RXJ' name.
The Right Ascension of the X-ray position of the cluster of galaxies in the selected equinox, as determined by the authors' VTP (Voronoi tesselation and percolation) algorithm. This was given in J2000 decimal degrees to a precision of 0.001 degrees in the original table.
The Declination of the X-ray position of the cluster of galaxies in the selected equinox, as determined by the authors' VTP (Voronoi tesselation and percolation) algorithm. This was given in J2000 decimal degrees to a precision of 0.001 degrees in the original table.
The Galactic Longitude of the cluster of galaxies.
The Galactic Latitude of the cluster of galaxies.
The column density of Galactic Hydrogen from Stark et al. (1992, ApJS, 79, 77), in atoms cm^-2.
The accumulated RASS exposure time, in seconds.
The ROSAT Position Sensitive Proportional Counter (PSPC) count rate in Pulse Height Analyzer (PHA) channels 11 to 235 as determined by VTP.
The equivalent radius sqrt(A_VTP/pi), where A_VTP is the VTP area, of the X-ray source detected by VTP, in arcminutes.
The final PSPC count rate in PHA channels 11 to 235 based on the original VTP count rate. Statistical corrections for low-surface-brightness emission that was not directly detected and for contamination from point sources have been applied.
The error in the final PSPC count rate CR according to equation (4) of paper I, Delta_CR/CR = 2.29(CR*Texp)^-0.48. The fractional uncertainty in the energy flux and the X-ray luminosity can be assumed to be the same as the fractional count rate error.
The intra-cluster medium (ICM) gas temperature used in the conversion from count rates to energy fluxes, in keV. Where available, measured X-ray temperatures taken from the compilation of David et al. (1993, ApJ, 412, 479) are used in the conversion; for the remainder (those with values of tx_flag of 'e'), the ICM gas temperature was estimated from the bolometric X-ray luminosity of the clusters using the L_x - kT relation quoted in section 6 of Paper I.
This parameter is a flag which is set to 'e' to indicate that the temperature has been estimated from the L_x - kT relation quoted in section 6 of Paper I.
The measured redshift of the cluster of galaxies.
The unabsorbed X-ray energy flux in the 0.1 - 2.4 keV band, in erg/s/cm^2.
The intrinsic X-ray luminosity in the 0.1 - 2.4 keV band and in the cluster rest frame, in erg/s.
The reference code for the quoted redshift value. For objects from the main sample (Paper I), the HEASARC has appended the letter M in front of the original numerical code: the key for these objects can be found in ftp://cdsarc.u-strasbg.fr/pub/cats/J/MNRAS/301/881/refs.dat.gz. For objects from the low-flux extension (Paper IV), the HEASARC has appended the letter E in front of the original numerical code: the key for these objects can be found in ftp://cdsarc.u-strasbg.fr/pub/cats/J/MNRAS/318/333/refs.dat.gz.
This parameter contains flags about the clusters' redshift, contamination, extent and serendipity, as follows:
V = extended according to VTP, Voronoi tesselation and percolation S = extended according to SASS, Standard Analysis Sofware System (Voges et al., 1992, Proc. Satellite Symp. 3, ESA ISY-3, p. 223) c = likely contamination from point sources + = serendipitous VTP detection * = redshift z > 0.3
This HEASARC-created parameter indicates from which published paper the particular entry came: 'main' means it comes from the main sample listed in Table 3 of Paper I, whereas 'extd' means it comes from the low-flux extension listed in Table I of Paper IV.