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.
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.
onaxis_tm0_rmf_2023-01-17.fits.gz