Date: 17-Apr-2023

#Introduction
The files are designed for simulations with XSPEC and contains the response files and background for the HET and LET. 
These files will be regularly updated as more instrument information becomes available. With each update the version number will increase.

#V06 -> V07 major changes
	HET
	- Background has decreased
	- Effective area CBE (current best estimate)
	- Energy dependent PSF for PSFcor files
	- optimized extraction region of R=18 arcsec
	LET
	- Background has decrease and same as Athena
	- Effective area CBE
	- HPD = 3.5"
	- optimized extraction region of R=8 arcsec


# List of files
##HET
HEXP_HET_v07.arf			- The HET effective area; no psf correction; includes 10% structural obscuration and detector QE
HEXP_HET_v07_x2.arf		- same as above but for two modules

HEXP_HET_v07_PSFcor.arf		- The HET effective area; Energy dependent PSF; ; optimized extraction R=18 arcsec; includes 10% structural obscuration and detector QE
HEXP_HET_v07_PSFcor_x2.arf	- same as above but for two modules

HEXP_HET_v07_FoVavg.arf		- The HET effective area; no psf correction; averaged over 0-5 arcmin;includes 10% structural obscuration and detector QE 

HEXP_HET_v07.rmf			- The HET RMF; based on NuSTAR; Simulated up to 220 keV; excludes QE

HEXP_HET_v07_L1_R18arcsec_Ln25keV.bkg	- THE HET background; based on 0.5xNuSTAR; extrated for R=18arcsec; includes a complex of detector lines at 25keV
HEXP_HET_v07_x2_L1_R18arcsec_Ln25keV.bkg	- same as above but for two modules

##LET
HEXP_LET_v07.arf			- The LET effective area; no psf correction; based on G5 with 25% structural obscuration and detector QE + OBF (200nm)

HEXP_LET_v07_PSFcor.arf		- The LET effective area; optimized for R=8 arcsec extraction; based on G5 with 25% structural obscuration and detector QE + OBF (200nm)

HEXP_LET_v07_FoVavg.arf		- The LET effective area; no psf correction; averaged over 0-5 arcmin; based on G5 with 25% structural obscuration and detector QE + OBF (200nm)

HEXP_LET_v07.rmf			- The LET RMF based on MPE DEPFETT

HEXP_LET_v07_L1_bkg_R8arcsec.bkg	- Using Athena WFI simulated background; extrated for R=8arcsec

# Notes
## General Simulation Remarks

To do a realistic simulation the PSFcor files with the matched background should be used.

These files can be used in XSPEC with fakeit as for example:
xspec> HEXP_HET_v07_x2_L1_R18arcsec_Ln25keV.bkg & HEXP_HET_v07.rmf & HEXP_HET_v07_PSFcor_x2.arf & y & & simulated.pha & exposuretime

Use these 'safe' fitting ranges
For the HET use 2.-80. keV
For the LET use 0.1-25. keV

## Background

The background files are matched to the PSFcor ARF files so that both have the same extraction region.

If a different scaling is desired, for example due to a different extraction region size for extended targets, it can be achieved by modifying the exposure time keyword in the background file. INCREASING the exposure time will DECREASE the background rate. Beware of the SIXTE_rate background column. Do not attempt to use this for anything as it is only intended for SIXTE.

### LET background notes

The LET background is flat and is based on the Athena WFI simulations at L1. Real backgrounds between 0.1 - 0.3 keV have a very steep tail which is not understood and is not included here. 

## Extended targets

Use the FoV averaged ARF or the ARF without PSF correction added. To scale the background region to the desired size, just modify the exposure keyword in the background header. If you desire a background that covers TWICE the area then REDUCE the exposure time by half to INCREASE the counts/c in the background region.

## PSF correction

The current best estimate of the PSF for the LET is 3.5". 
The current best estimate of the PSF for the HET is that it will be energy dependent at higher energies (>20 kev). These numbers are still TBD, and what is in the files now conservative.
We have optimized the extraction region for faint sources for both LET and HET. For LET it is 0.88, so 88% of the photons are within the extraction region. For the HET that number is now energy dependent.


# Contact
All files were generated by Kristin K. Madsen. For issues or suggestions for improvement contact: kristin.c.madsen@nasa.gov