The main purpose of FLIX is to produce estimates of the upper-limit to the X-ray flux at a given point in the sky for there to have been no source detected there in the 2XMMi survey. This upper-limit flux is found empirically using the algorithm described by Carrera et al (2007) The XMM-Newton Serendipitous Survey, IV. The AXIS X-ray source counts and angular clustering. A copy of the preprint may be found in astro-ph at http://www.eprintweb.org/S/article/astro-ph/0703451 - the algorithm appears in Appendix A. These upper-limits use the DETMSK to find which pixels in the image are valid, EXPMAP data to find the exposure time, and BKGMAP data to determine the fitted background level.
In addition FLIX provides other information:
Results are returned as a web page with an HTML table per celestial position, and a FITS file is also produced with a binary table containing one row per observation which contains useful information. This may be downloaded as soon as the HTML output is complete, and examined with utilities such as FV or TOPCAT.
The program is a CGI script which can be run from http://www.ledas.ac.uk/flix/flix.html
The following parameters may be entered on the web form:
The input file is a plain text file with one position per line. This should contain an RA, a DEC; optionally a source name or identifier may follow. The RA and DEC can be given in decimal degrees, or sexagesimal hours, minutes, seconds (for RA) and degrees, arc-minutes, and arc-seconds (for DEC). The sexagesimal components may be separated by a space or colons, and the RA and DEC may be separated by spaces, a comma, or a vertical bar. Thus all of the following formats are allowed:
8.51332233 -5.40595761 decimal degrees
12:30:45.12345 -12:34:56.789 sexagesimal hms
12 30 45.12345 -12 34 56.789 with spaces rather than colons
12 30.75 -12 34.95 if hours and mins only need decimal minutes
8.51332233, -5.40595761 decimal degrees
12:30:45.12345, -12:34:56.789 sexagesimal hms
12 30 45.12345, -12 34 56.789 with spaces rather than colons
12 30.75, -12 34.95 if hours and mins only need decimal minutes
75 59 59 89 59 59 near maximum dec
75 59 59 00 00 12 mostly zeros for dec
0 0 57 -0 00 12 negative sign for dec
Note that for each position the program has to read around compressed 40 data product files before performing the flux calculations, which takes from 5 to 10 seconds per position typically.
For positions in the sky which XMM did not cover a null row is produced in the HTML table, but no rows are written to the FITS table. For some positions there may be multiple observations containing data, up to 30 in a few cases. The FITS file contains one row per observation matching each position, so it may have more rows than there are positions in the input text file.
The FITS file will not be downloadable until the processing is completed; it will be retained on the server for at least 24 hours before being deleted.
The columns in the FITS table are described below; the
columns in the HTML table are similar, but also contain a
thumbnail image if requested.
|RA||Right ascension of point of interest (decimal degrees)|
|DEC||Declination of point of interest (decimal degrees)|
|NAME||Name from input list, if any|
|REVOLUT||Revolution i.e. orbit number|
|RA_PNT||Pointing axis R.A. (decimal degrees)|
|DEC_PNT||Pointing axis declination (decimal degrees)|
|OFFAXIS||Approximate distance of point of interest from pointing axis (arcmins)|
|OBJECT||Target name of the original observation|
|OBSERVER||Name of principal investigator of original observation|
|DATE_OBS||Date and time at which observation was started|
|DATE_END||Date and time at which observation ended|
|M1/M2/PN_ACTIVE||Duration for which instrument was active (seconds)|
|M1/M2/PN_FILTER||Filter name for each instrument|
|M2/M2/PN_SUBMODE||Data submode - see XMM handbook for more details|
|M1/M2/PN_MASKFRAC||Fraction of pixels providing data around this position|
|M1/M2/PN_8_EXP||Exposure time for whole band (seconds)|
|M1/M2/PN_band_FUP||Flux upper limit for each instrument and bands 1-9 (erg/sq cm/sec)|
|M1/M2/PN_band_FES||Flux estimate for each instrument and band using counts in circle and fitted background level (erg/sq cm/sec)|
|M1/M2/PN_band_FER||Standard error on above flux estimate (erg/sq cm/sec)|
|SRCID||Source identifier (note not DETID) of the nearest source in the 2XMMi survey|
|SRCDIST||Distance of this source from the specified position (arcsecs)|
In the HTML table the SRCID and SRCDIST values for the five nearest sources are shown, but only the nearest is listed in the FITS file to avoid format complications.
Author: Clive Page, University of Leicester. email: cgp (at) star.le.ac.uk
Date: 2009 January 27.