mkgisbgd -- Create exposure corrected blank sky spectrum and image from point-source removed blank sky event files
mkgisbgd filelist specfile gtifile output
mkgisbgd creates 'pure' blank sky background spectrum and image without point sources.
mkgisbgd requires blank sky event files in which point sources are removed, and the removed detector area is indicated in the 'mask' image which should be in the primary of the event file. These files may be taken from the ASCA CALDB, at ftp://legacy.gsfc.nasa.gov/caldb/asca/gis/bcf/bgd/no_sources. User may create such source removed event files by themselves for mkgisbgd.
In this background dataset, GIS high latitude observations taken between 1993 June and 1995 December are used. Total exposure time is approximately 2.1 Msec. The 'mask files' are supplied by Yoshitaka Ishisaki (Tokyo Metropolitan University, email@example.com). Sources brighter than ~1e-13 erg/s/cm2 in 2-10 keV are removed. Find Y. Ishisaki's doctoral thesis entitled "Spectra and Large-scale Isotropy of the Cosmic X-ray Background from ASCA Observations" (available at http://mpuax5.phys.metro-u.ac.jp/~ishisaki/dron.ps.gz) for more details.
The blank sky event lists are 'screened' with the standard criterion used in the ASCA REV2 pipe-line processing. Namely, these event files (having the 'evt' suffix) are taken from the 'screened' directory in the ASCA archives, and subsequently point sources are removed using the 'fmaskfilt' ftool with the mask images. The REV2 stander screening criterion is the same as the 'ascascreen' standard criterion. Therefore, most users who adopt the standard screening criterion will not need further screening of the event files.
We also have made good time interval files corresponding to the ascascreen 'strict' criterion, which are in the same CALDB ftp area (gis_strict.gti). Users who use the 'strict' criterion for their sources should apply this GTI file when running mkgisbgd.
The exposure time of the blank sky observation is calculated taking account of the effect of masking the point sources. The algorithm of exposure time calculation is found in the article "Method of GIS Background Subtraction", Ikebe et al., ASCA Newsletter number 3 (available at http://heasarc.gsfc.nasa.gov/docs/asca/newsletters/gis_bkgd_sub3.html.)
The detector region to use is taken from the WMAP of the input spectral file. The BACKSCAL keyword of the input spectral file is copied to the output spectral file to make sure the correct background normalization. The output background file is ready to be used in XSPEC for the background of the input spectral file.
mkgisbgd g2file_list 50msec.spec NONE 50msec.bgd clobber=yes
Using the point-source-removed blank sky event files listed in 'g2file_list', make a background file '50msec.bgd' corresponding to the spectral file '50msec.spec'. No GTI file is specified ('NONE'). If the output file '50msec.bgd' exists, that is overwritten. Content of the g2file_list may look like, bfn1_g2_no_source.evt bfn2_g2_no_source.evt bfn3_g2_no_source.evt bfn4_g2_no_source.evt draco1_g2_no_source.evt draco2_g2_no_source.evt draco3_g2_no_source.evt lss101_g2_no_source.evt lss102_g2_no_source.evt lss103_g2_no_source.evt .....
Ken Ebisawa (firstname.lastname@example.org) at ASCA GOF. Questions and comments to email@example.com.