eROSITA Calibration Products in DR1

The Auxiliary Response Files (ARFs) contain the telescope's effective area information. The ARFs result from multiplying the telescope's geometric area with the filter transmission and the detector's quantum efficiency. The Response Matrix Files (RMFs) contain information about the spectral resolution and energy redistribution. For eROSITA, if you installed the eROSITA Science Analysis Software System (eSASS), you can easily obtain the ARFs and RMFs from the eROSITA Calibration Database (CALDB), or by running the srctool task. These files are by default created for all patterns (PATTERN=15).

Please note that the correct ARF file to use when taking exposure values from merged exposure maps is the TM0 on-axis one. This is because the exposure values in merged exposure maps from expmap are already corrected for the number of telescope modules in use and the vignetting of the telescope. If expmap exposure values are combined with survey-averaged ARF files, then the vignetting will be double-counted. The individual ARFs are useful if you would like to compare the differences in effective area between TM0, TM8 and TM9, in survey and pointed modes. A tutorial about ECF and flux calculations can be found here.

Please also note that srctool uses a different definition for exposure than the standard exposure maps. The exposure in srctool products is the time spent looking at the source, corrected for dead time. The effects of vignetting and the number of telescope modules in use are accounted for in the srctool ARF file instead.

ARFs

TM0, contains all seven cameras

TM8, contains the five cameras with on-chip filter (TM1, TM2, TM3, TM4 and TM6)

TM9, contains the two cameras without on-chip filter (TM5 and TM7)


The on-axis ARFs can be produced by using FTOOLS addarf with the eSASS calibration files. For example,

addarf list='tm5_arf_filter_000101v02.fits tm7_arf_filter_000101v02.fits' weights='1 1' \
       out_arf=onaxis_tm9_arf_filter.fits

The survey ARFs were produced as follows:

srctool eventfiles=em01_090159_020_EventList_c020.fits srccoord='fk5;87.7,-69.4' todo='SPEC RMF ARF' \
        srcreg='circle * * 0.5s' backreg=NONE exttype=TOPHAT extpars='2' \
	psftype=NONE prefix=erass1_090159_novign_ xgrid=0.005 tstep=0.01 clobber=yes

For reference, these use a small region size (to avoid the correction for part of the region outside the FoV). A small xgrid is due to the small region, flat source model, and no PSF correction. Note that the position is unimportant (if it is in the tile). Any position with reasonable scan coverage should work.

RMFs