detect HEADAS help file

NAME

detect --> detects all sources in a given PSPC FITS image having a significance equal to or greater than a user specified significance, and having a count rate equal to or greater than a user specified count rate.

This tool is to be used only for PSPC observations.

USAGE

detect evtmapfil expmapfil chanmin chanmax sig count_rate

DESCRIPTION

DETECT will identify point sources in the field covered by a single PSPC observation and create a point source mask for that field. It uses SLIDING BOX algorithm with the slight improvement that the box is a circle where the radius is a function of off-axis angle. The source identification threshold can be set for both count rate and significance. The program sets a source radius at 90% encircled energy radius and the background annulus at 2.5 times the 90% encircled energy radius. If fewer than 4 counts are found in the background annulus, the average background for the observation is used. The significance is determined using POISSON statistics, but does not consider the number of trials.

DETECT requires a PSPC image in some energy band along with an exposure map in that energy band; the PSPC image can be constructed for eg. by using XSELECT on the PSPC events file (the *_bas.fits file) for a given observation. The PSPC exposure map can be created by running the FTOOL PCEXPMAP.

DETECT will generate 2 output files:

1. an image file containing the sources circled with 90% PSF

2. an ascii file containg the details of the sources, e.g., RA, DEC, count rate, radial distances from the center of the image file etc.

WARNINGS ON USAGE

Only PSPC observations are currently supported in this task.

DETECT can be used with the BROAD-BAND images (*_im1.fits) and exposure maps (*_mex.fits) available from the ROSAT data archive, but the headers in the primary arrays of these FITS files need to have included the values of the CHANMIN and CHANMAX keywords. To do this first find the values of the PIMIN and PIMAX keywords (typically, PIMIN=11 and PIMAX=235). Create a file called chan_bnds.txt with 2 entries:

CHANMIN 11 CHANMAX 235

in which the entry after CHANMIN is the value of PIMIN, and similarly for CHANMAX. Then use the ftool fmodhead to update the header of the broad-band image file and the broad-band exposure map:

% fmodhead rp900176n00_im1.fits+0 chan_bnds.txt % fmodhead rp900176n00_mex.fits+0 chan_bnds.txt

PARAMETERS:

(evtmapfil="EVTMAPFIL") [character string]

The name of the input FITS image file

(expmapfil="EXPMAPFIL") [character string]

The name of the input exposure map file (obtained running the tool PCEXPMAP, using the detmap file and not devignetted map).

(instr="INSTR") [string]

Name of instrument PSPC/HRI. This parameter is not used at present as it was designed to be used when both HRI and PSPC are supported. So, it is basically inactive till HRI is supported.

(chanmin="CHANMIN") [integer]

Lower bound channel number. This should be same as the minimum channel number, as given by the CHANMIN keyword in the FITS image or exposure map.

(chanmax="CHANMAX") [integer]

Upper bound channel number. This should be same as the maximum channel number, as given by the CHANMAX keyword in the FITS image or exposure map.

(sig="SIG") [real]

Significance level wanted.

(count_rate="COUNT_RATE") [real]

Threshold count rate. Source with count rate equal to or higher than this value will be returned by DETECT

(outfil = "detect.img") [string]

The output image filename with sources encircled.

(qmask = "no") [boolean]

Whether masking file is needed. Masking file is the file containing the sources masked.

(chatter = "9") [integer]

Flag to set the chattyness at execution. Default value is set to 9, which gives the user the task version and few warnings. Lower/higher values produces quieter/verbose output on the screen.

(clobber = "false") [boolean]

Flag specifying whether or not a pre-existing file with the same name as that requested as the output file from this task will be overwritten.

EXAMPLE:

In this example we run detect on rp900176n00_im1.fits, a broad-band image of the Carina nebula. First we updated the headers with the values of the CHANMIN and CHANMAX keywords:

% fmodhead rp900176n00_im1.fits+0 chan_bnds.txt % fmodhead rp900176n00_mex.fits+0 chan_bnds.txt

where the file chan_bnds.txt contains 2 entries

CHANMIN 11 CHANMAX 235

then




% detect 
  --- Only PSPC is supported for FTOOLS4.0 (June, 1997)
  ------ Working on HRI support for later release
Enter filename for events map:[rp900176n00_im1.fits] rp900176n00_im1.fits 
Enter filename for exposure map:[rp900176n00_mex.fits]rp900176n00_mex.fits 
Enter lower PI channel no.:[11] 11
Enter upper PI channel no.:[235] 235
Enter statistical significance:[10] 6
Enter count rate threshold:[0] 
 ** detect 1.0.1
 source detection filename = diag_8_7.dat
 ...
 ... mask file mask_8_7.fits        exists!
 ... no. of source detected =  101
 ** detect 1.0.1 completed successfully

BUGS:

Only PSPC observations are supported for the release in June 1997. There are currently no plans to include HRI observations.

LOG OF SIGNIFICANT CHANGES:

v1.0.0 (June, 1997) created

PRIMARY AUTHOR:

Banashree M Seifert

HEASARC, NASA/GSFC

http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp