Description

The task ebkgreg searchs for the most suitable position of a circle region to get the background estimation of any source in an EPIC-pn image.

This task has two processing modes: multiple sources from an input source list file or single-source from command-line arguments.

In the multiple sources case the input source list has to contain the following basic parameters for each source: celestial coordinates (RA, DEC), EPIC-pn counts (PN_CTS) and EPIC-pn offaxis information (PN_OFFAX). The extraction region radius for each source is obtained from a tabulated table and it depends on the counts and the off-axis values of the source. All of that mandatory information is included in the 'EPIC summary source list' from the standard distribution of the pipe-line processing. Additionally that source list can be created from srcmatch (follow the link for further information).

Alternatively the extraction region radius for each source can be present in the input source list as SRC_RAD. In this case this is the mandatory column in the input, but not PN_CTS and PN_OFFAX.

Only in the single-source mode the source basic information can be given via the command-line arguments, x, y and r, where x,y are the celestial coordinates of the source and r is the source extraction radius for source products in arcsec. Depending on the coordtype the source position could be RA,Dec or X,Y Sky coord.

The algorith will search for that background position in the same CCD where the source is located.

The background extraction region always have a radius larger than 3 pixels, otherwise no background is calculated.

**Table 1:** **Input and Output quantities**
Value	Description	Units
x	Source RA or X Sky coord	deg. or 0.05 arcsec pixel
y	Source Dec or Y Sky coord	deg. or 0.05 arcsec pixel
r	Source extraction radius	arcsec

bkg_ra_out	Background region center RA	deg.
bkg_dec_out	Background region center Dec	deg.
bkg_rad_arcsec_out	Background region radius	arcsec
bkg_x_out	Background region center X sky coord	0.05 arcsec pixel
bkg_y_out	Background region center Y sky coord	0.05 arcsec pixel
bkg_rad_phys_out	Background region radius	0.05 arcsec pixel