The Ariel Catalogue of X-Ray Sources (Warwick et al.; McHardy et al. 1981) Documentation for the Computer-Readable Version Susan E. Gessner September 1991 Doc. No. NSSDC/WDC-A-R&S 91-22 Contract NAS 5-28752 Prepared for: National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, MD 20771 Prepared by: ST Systems Corporation 4400 Forbes Blvd. Lanham, Maryland 20706 Abstract This document describes the overall file structure and individual data fields of the computer-readable version of The Ariel Catalogue of X-Ray Sources distributed by the Astronomical Data Center, NASA Goddard Space Flight Center. It is a compilation of data describing 251 X-ray sources divided into three files which consist of a low latitude sources file, a high latitude sources file, and a reference file. Position of the source and the corners of an error box enclosing it are listed in celestial coordinates. Maximum, minimum, and average flux vlaues are given as are suggested identifications and references for each source. 1 Introduction A copy of this document should be distributed with every copy of the computer-readable catalogue. 1.1 Description The Ariel Catalogue of X-Ray Sources (3A; Warwick et al.; McHardy et al. 1981) is in three files which contain data identical to the tables published in the original reference, as follows: low latitude sources, high latitude sources, and references. The data in these files are in exactly the same format. The present document describes the overall file structure and the individual data fields. For references to authors mentioned in this document, see the source references. 1.2 Source References Warwick, R.S., et al. 1981, MNRAS, 197, 865 McHardy, I.M., et al. 1981, MNRAS, 197, 893 2 Structure 2.1 Each File as a Whole The 3A consists of 3 files. Table 1 gives the tape-file attributes that are the same no matter what computer the catalogue is copied for. All records are of fixed length. Detailed descriptions of the data files are given in the following sections. There are also attributes that will change from computer to computer if the catalogue has been distributed on tape. These attributes include block size, blocking factor, total number of blocks, density, number of tracks, and character coding (ASCII, EBCDIC). This information has not been included for tapes, but should always accompany secondary copies if any are supplied to other users or installations. Quotations in any of the following descriptions come from Warwick et al.; McHardy et al. (1981) unless otherwise noted. 1 ______________________________________________________________ The Ariel Catalogue of X-Ray Sources (Warwick et al.; McHardy et al. 1981) ______________________________________________________________ Record Record Number of File Contents Format Length Records ______________________________________________________________ 1 Low Latitude Sources Fixed 254 109 2 High Latitude Sources Fixed 254 142 3 Reference File Fixed 80 195 ______________________________________________________________ Table 1: Summary Description of Catalogue Files 2.2 Data (Files 1 and 2 of 3) The two data files, low latitude and high latitude sources, contain data in exactly the same format. Table 2 describes the data format of these files in detail. Detailed descriptions of certain fields in Table 2 are listed below. Ariel Name This designation consists of a "3A" followed by the celestial coordinates of the source position. Alternative Names Up to three other names are given for the X-ray source. These designations are generally derived from observations by the following satellites: A Ariel V; both earlier SSI and rotation colli- mator observations. 2A Ariel V; see Cooke et al. (1978a). H HEAO-1; A2 and A3 experiments. 1E Einstein observatory MX OSO-7 or SAS-3; see Markert et al. 1976. 4U Uhuru; see Forman et al. 1978. In addition, common names (e.g. SCO X-1, Cen X-3) and "source names obtained from earlier, mainly rocket, observations derived from the galac- tic coordinates of the source (e.g. GX 301-2)" are listed in this field. References to these names may be found in Forman et al. (1978) or Bradt, Doxsey, & Jernigan (1979) respectively. Otherwise, a ref- erence identification enclosed in brackets may be listed here or the other information field; these refer to references located in file 3 (see section 2.3). Position The "position of maximum probability density for the X-ray source location" given in degrees of right ascension and declination (1950.0). 2 _______________________________________________________________________________ Suggested Default Bytes Units Format Value Data _______________________________________________________________________________ 1-10 _ A10 _ Ariel Name 11-40 _ A30 _ Alternative Names 41-46 deg F6.2 _ R.A. (1950) 47-52 deg F6.2 _ Dec. (1950) 53-58 deg F6.2 blank Error Box Corner: R.A. 59-64 deg F6.2 blank Error Box Corner: Dec. 65-70 deg F6.2 blank Error Box Corner: R.A. 71-76 deg F6.2 blank Error Box Corner: Dec. 77-82 deg F6.2 blank Error Box Corner: R.A. 83-88 deg F6.2 blank Error Box Corner: Dec. 89-94 deg F6.2 blank Error Box Corner: R.A. 95-100 deg F6.2 blank Error Box Corner: Dec. 101-105 deg**2 F5.3 blank Area: Error Box 106-110 _ A5 _ Position Code 111-118 count/s F8.2 blank Average Flux 119-126 count/s F8.2 blank Error: Average Flux 127-134 count/s F8.2 blank Minimum Flux 135-142 count/s F8.2 blank Error: Minimum Flux 143-150 count/s F8.2 blank Maximum Flux 151-158 count/s F8.2 blank Error: Maximum Flux 159 _ A1 blank Variability Code 160-179 _ A20 _ Identification 180-254 _ A75 _ Other Information _______________________________________________________________________________ Table 2: Data Files Record Format 3 Error Box Right ascension and declination (1950.0) of the four corners of "a rectangle enclosing an elliptical approximation to a 90 per cent confidence contour for the source location." These are listed only for sources "for which the SSI observations provide in- formation of a precision which is comparable to, or better than, previously reported X-ray measurements (above 2 keV)." These are sources with a position code of `3A'. Area The area within the 90 per cent confidence contour. Position Code The position code indicates in what manner the position of the X-ray source was obtained. Thus, the source positions are not limited to those de- rived from SSI observations. "Accurate X-ray po- sitions (notably from SAS-3 and HEAO-1 satellite observations) as well as optical and radio positions are available for many of the bright, low latitude X-ray sources." The position codes are as follows: 3A Position based on SSI observations X-RAY Position obtained from other published X-ray observations OPT Position obtained from published obser- vations of the optical counterpart of the X-ray source. RAD Position obtained from published obser- vations of the radio counterpart of the X-ray source. References to these published source positions may be found in Bradt et al. (1979) unless a reference identification enclosed in brackets follows a "POS" flag in the other information field; these refer- ences may be found in the reference file. Source Flux Average, minimum, and maximum flux values for X-ray sources in SSI count s**-1 . Error values (+/- 1 sigma) follow each flux value. "All flux determina- tions and variability code assignments were made from summed-orbit records." Variability Code Flux variability codes are assigned as follows: S Steady: The average flux is the weighted mean flux from all observations. The minimum and maximum flux fields contain no data. 4 I Irregular: The average, minimum, and maximum flux values are lisited. These are sources which the SSI determined to be periodic (e.g. HER X-1). This class also includes those sources "seen to exhibit flaring where emission was also observed by the SSI outside of the flares (e.g. 3A 1102+385 = MKN 421)" and "those with a formal probability < 1 per cent that the X-ray light curve could result from steady X-ray emission." T Transient: Only the maximum flux is listed. This class includes sources that would gener- ally not be detected by SSI observations because of their short duration (<= 50 days). Such outbursts often exhibit dramatic flux in- creases (see Kaluzienski 1977; Cominsky et al. 1978), some of which are recurrent (e.g. A 0535+26). For a transient source, the SSI did not detect any X-ray emission except for that which was a result of the outburst. Identification The suggested identification of the X-ray source. The method by which these were obtained in the high lat- itude survey is described in section five of McHardy et al. (1981). Otherwise, references to identifica- tions taken from previously published results are located in file 3, referenced in brackets in the other information field. The high latitude survey file contains an identifica- tion code (bytes 170-179, A20 FORTRAN format) within this field which expresses confidence in the identification as follows: **** Almost certain: There are three categories of evidence which support the identification. They are as follows: "(a) correlated X-ray/ optical or X-ray/radio variability; (b) the X-ray emission has been spatially resolved e.g. sources proposed as clusters of galaxies; (c) the object is inside a very precise (dimension approx. few arc seconds) X-Ray error box." More than one category of evidence may support any given identification. *** Very likely: the source is contained within a "very small (dimensions <= 1 arcmin) error box." ** Probable: the source is contained within or very close to a "small (<= 0.1 deg**2) 3A error box or inside a larger 3A error box and has supporting evidence." 5 * Possible: the source identification is a result of positional coincidence only. The supporting evidence may be referenced in other information field. Other Information This field mainly contains additional information which is often followed by a reference identification in brackets. References for the identification and position code fields are listed in a similar fashion The latter is always indicated by a "POS" flag. The low latitude survey (file 1) contains references to earlier papers based on SSI observations of sources in the catalogue; these are indicted by a "SSI" flag followed by the reference identification in brackets. Also listed is any periodic behavior in the X-ray emission from the source. Note that " `Seyfert' indicates a `Seyfert type I' galaxy, and `Hexelg' refers to any other type of high extinction emission line galaxy. It is probable that almost all of the latter are, in fact, `Seyfert type II' galaxies." See Warwick et al.; McHardy et al. (1981) for additional information concerning this field. 2.3 Reference file (file 3 of 3) The reference file contains all references found in the alternative names and other information fields which are indicated by a reference identification, a letter and number combination, in brackets. The full references are listed alphabetically in the file by the reference identification. Table 3 describes the data format of this file. ___________________________________ Suggested Bytes Format Data ___________________________________ 1-3 A3 Reference ID 4-10 7X Blank 11-80 A70 Full Reference ___________________________________ Table 3: Reference File Format 3 Remarks and Modifications The Ariel Catalogue of X-Ray Sources was received on magnetic tape by the Astronomical Data Center (ADC), NASA Goddard Space Flight Center, from the Centre de Donnees de Stellaires (CDS), Strasbourg in March 1989. The original tape consisted of five files in the same format as the published catalogue. In addition to the four data files, a description file was also included; this has been incorporated into this document. A FORTRAN program was run to check the validity of each field according to its data type and value. 6