HRC-S/LETG Grating Response Matrices
==============================================================
[ /data/snafu/kashyap/GRMF/RSP/README.GRSP ; vlk ; 2001dec18 ]
The CIAO tools MKGRMF and MKGARF allow creation of grating
ARFs and RMFs for a specified dispersion order. However,
because orders cannot be separated in the HRC-S, it is
necessary to combine these ARFs and RMFs into a single
response matrix in order that HRC-S/LETG spectra may be
analyzed in XSPEC or Sherpa.
The following files are the combined response matrices for
orders 1 through 6, obtained by multiplying the CAL product
gARFs (available from the LETG Observer Information page at
http://asc.harvard.edu/cal/Links/Letg/User/Hrc_QE/ea_index.html )
with the RMFs currently in CALDB.
rspdir/hrcslegp12.rsp -- gRSP(+1)+gRSP(+2)
rspdir/hrcslegp1t3.rsp -- gRSP(+1)+gRSP(+2)+gRSP(+3)
rspdir/hrcslegp1t4.rsp -- gRSP(+1)+gRSP(+2)+gRSP(+3)+gRSP(+4)
rspdir/hrcslegp1t5.rsp -- gRSP(+1)+gRSP(+2)+gRSP(+3)+gRSP(+4)+gRSP(+5)
rspdir/hrcslegp1t6.rsp -- gRSP(+1)+gRSP(+2)+gRSP(+3)+gRSP(+4)+gRSP(+5)+gRSP(+6)
rspdir/hrcslegm12.rsp -- gRSP(-1)+gRSP(-2)
rspdir/hrcslegm1t3.rsp -- gRSP(-1)+gRSP(-2)+gRSP(-3)
rspdir/hrcslegm1t4.rsp -- gRSP(-1)+gRSP(-2)+gRSP(-3)+gRSP(-4)
rspdir/hrcslegm1t5.rsp -- gRSP(-1)+gRSP(-2)+gRSP(-3)+gRSP(-4)+gRSP(-5)
rspdir/hrcslegm1t6.rsp -- gRSP(-1)+gRSP(-2)+gRSP(-3)+gRSP(-4)+gRSP(-5)+gRSP(-6)
where gRSP(order) == gARF(order)*gRMF(order)
Notes:-
1. When using these gRSPs within, e.g., Sherpa, do NOT specify
a gARF, since the gRSPs already include the gARFs.
2. These responses have been tested extensively with continuum
sources PKS 2155-304 and RX J1856.5-3754 and have been shown
to produce reasonable results.
2.1 Best-fit values for PKS 2155-304 are
xwabs.nH = 0.0141566 10^22/cm^2
xspowerlaw.PhoIndx = 2.38867
xspowerlaw.norm = 0.0988854 photons/keV/cm**2/s at 1 keV
which compares favorably with independent estimates of
NH=(1.3-1.4)e20, PhoIndx=2.35-2.45, norm=0.09-0.1
(D.Pease, H.Marshall)
2.2 Best-fit values for RX J1856.5-3754 are
xswabs.nH = 0.0114488 10^22/cm^2
xsbbody.kT = 0.0615671 keV
xsbbody.norm = 0.000302328 L39/(D10)**2
which are close to independently determined estimates of
NH=0.008-0.011, kT=0.059-0.064, norm=0.00027-0.00032
(A.Fruscione)
3. Care must be exercized in fitting line spectra using these
response matrices, because of various limitations. e.g.,
3.1 There exist shifts in the wavelength scale that are
not necessarily accounted for in the RMFs, so fitting
simultaneously to say a 1st order and 3rd order line
may result in a poor fit for the latter because the
predicted high-order location differs from the true
location.
3.2 There also appear to be differences between the +ve
and -ve order LSFs that are not (yet) included in
the gRMFs, so simultaneously fitting +ve and -ve order
lines is not recommended.
3.3 Beware of using the poly1d models for local continuum
while fitting higher-order lines -- because there is
no way to place wavelength limits on the continuum, the
model predictions will include contributions from the
lower-order also.
3.4 The same issue as above applies to independently modeling
the background as power-laws (as recommended in the CIAO
analysis threads).
3.5 The individual high-order gRMFs are stored at higher
resolution than the 1st order gRMF. However, the final
gRSP is perforce required to be on the same grid as the
1st order gRMF. Hence detailed information may be lost
from the high-order response. If this detail is critical,
you must use the individual gRMFs separately.
4. These response matrices were produced by sequentially adding
gARFs and gRMFs of higher orders to that of the 1st order using
IDL routines from PINTofALE ( http://hea-www.harvard.edu/PINTofALE/ )
and the IDLAstro library. Example code that may be used to derive
hrcslegp1t3.rsp is given below, and may be generalized to any number
of orders.
4.1 The example code uses canned gARFs, which are obviously not
correct at plate gaps. If you use the output of MKGARF, note
that that does not include the extraction efficiencies, so
prior to forming the gRSPs, the gARFs must be multiplied by
the appropriate extraction efficiencies.
4.2 The PINTofALE program ADDRSP() only adds two RMFs at a time;
hence the need for the step-by-step approach detailed below.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; the following PINTofALE routines are required
.compile rd_ogip_rmf rdarf addrsp wrt_ogip_rmf ogipzip kilroy
; where are the gRMFs?
caldb=getenv('CALDB')
rmfdir=caldb+'/data/chandra/tel/grating/letg/cpf/rmf/'
; gARFs may be downloaded from
; http://asc.harvard.edu/cal/Links/Letg/User/Hrc_QE/ea_index.html
; it is assumed that they are then placed in subdirectory arfdir/
; read in 1st order gRMF and gARF
rm1=rd_ogip_rmf(rmfdir+'/hrcleg1D1999-07-22rmfN0002.fits')
ea1=rdarf('arfdir/test_letgs_NOGAP_EA_s001031_p.fits',ostr1)
; interpolate the gARF to the grid of the gRMF
ee=0.5*(rm1.elo+rm1.ehi)
eaee=0.5*(ostr1.ELO+ostr1.EHI) & effar1=interpol(ea1,eaee,ee) > 0
; read in 2nd order gRMF and gARF
rm2=rd_ogip_rmf('rmfdir/hrcleg2D1999-07-22rmfN0002.fits')
ea2=rdarf('arfdir/letgs_EA_001031_o02p_s8192.fits',ostr2)
; interpolate gARF to grid of gRMF
ee=0.5*(rm2.elo+rm2.ehi)
eaee=0.5*(ostr2.ELO+ostr2.EHI) & effar2=interpol(ea2,eaee,ee) > 0
; combine 1st and 2nd orders
rsp12=addrsp(rm1,rm2,ea1=effar1,ea2=effar2,verbose=10)
; read in 3rd order gRMF and gARF
rm3=rd_ogip_rmf('rmfdir/hrcleg3D1999-07-22rmfN0002.fits')
ea3=rdarf('arfdir/letgs_EA_001031_o03p_s8192.fits',ostr3)
; interpolate gARF to grid of gRMF
ee=0.5*(rm3.elo+rm3.ehi)
eaee=0.5*(ostr3.ELO+ostr3.EHI) & effar3=interpol(ea3,eaee,ee) > 0
; add 3rd order to previously obtained combined 1st and 2nd order
rsp1t3=addrsp(rsp12,rm3,ea2=effar3,verbose=10)
; write out to a disk file for use with Sherpa or XSPEC
wrt_ogip_rmf,rsp12,'rspdir/hrcslegp12.rsp',telescop='CHANDRA',instrume='HRC',$
filter='NONE',detnam='HRC-S',grating='LETG',chantype='PI',$
cvsd='1999-07-22',cvst='00:00:00',mission='AXAF',$
hduclas3='FULL',creator='wrt_ogip_rmf.pro'
wrt_ogip_rmf,rsp1t3,'rspdir/hrcslegp1t3.rsp',telescop='CHANDRA',instrume='HRC',$
filter='NONE',detnam='HRC-S',grating='LETG',chantype='PI',$
cvsd='1999-07-22',cvst='00:00:00',mission='AXAF',$
hduclas3='FULL',creator='wrt_ogip_rmf.pro'