XIS Blank Sky Background Files
The blank sky background files released here are based on the data with a relatively short exposure of 96 ks. Those who want to simulate spectra for a longer exposure than 100 ks should use the night earth background files and add the CXB and Galactic diffuse background as model componets.
Please note that these files are based on somewhat old data. However, we believe it is indicative of the approximate level of the blank sky (particle+cosmic X-ray) background for Cycle 8 observations.
The XIS team has provided a set of blank sky background files suitable for the preparation of proposals.
The spectral files have been created from the Lockman Hole observations on May 3, 2007. The aim point of the observation was RA = 162.9375, Dec = 57.26667.
The spectra were extracted from a circular region of a radius of 6 mm centered at the XIS/HXD nominal positions. Because the unit of the BACKSCAL keyword changes with the coordinate system, spectra were created for both the DET and SKY coordinates. Two spectra, one for the BI sensor (XIS1) and the other for the sum of FI sensors (XIS0,3), have been extracted for each coordinate system and for each extraction region. Net exposures are 96.1 ks for both of FI and BI sensors.
This release consists of the following 16 files.
1. 4096 channel versions
- XIS nominal position (r=6mm):
- Sky Coordinates
- LH_xisnom6mm_sky_bi.pi.gz (XIS1)
- LH_xisnom6mm_sky_fi.pi.gz (Sum of XIS0,3)
- Detector Coordinates
- LH_xisnom6mm_det_bi.pi.gz (XIS1)
- LH_xisnom6mm_det_fi.pi.gz (Sum of XIS0,3)
- Sky Coordinates
- HXD nominal position (r=6mm):
- Sky Coordinates
- LH_hxdnom6mm_sky_bi.pi.gz (XIS1)
- LH_hxdnom6mm_sky_fi.pi.gz (Sum of XIS0,3)
- Detector Coordinates
- LH_hxdnom6mm_det_bi.pi.gz (XIS1)
- LH_hxdnom6mm_det_fi.pi.gz (Sum of XIS0,3)
- Sky Coordinates
Please use one of the above for simulation purposes with a matching set of RMF and ARF files.
2. 2048 channel versions
- XIS nominal position (r=6mm):
- Sky Coordinates
- LH_xisnom6mm_sky_bi2048.pi.gz (XIS1)
- LH_xisnom6mm_sky_fi2048.pi.gz (Sum of XIS0,3)
- Detector Coordinates
- LH_xisnom6mm_det_bi2048.pi.gz (XIS1)
- LH_xisnom6mm_det_fi2048.pi.gz (Sum of XIS0,3)
- Sky Coordinates
- HXD nominal position (r=6mm):
- Sky Coordinates
- LH_hxdnom6mm_sky_bi2048.pi.gz (XIS1)
- LH_hxdnom6mm_sky_fi2048.pi.gz (Sum of XIS0,3)
- Detector Coordinates
- LH_hxdnom6mm_det_bi2048.pi.gz (XIS1)
- LH_hxdnom6mm_det_fi2048.pi.gz (Sum of XIS0,3)
- Sky Coordinates
These versions have been rebinned into 2048 channels using a variable binning scheme for faster simulation. Please use one of the above with a matching rebinned RSP file.
Note on BACKSCAL: In the above files, the values of the BACKSCAL keyword are set correctly to reflect the size of the extraction region for the respective coordinate systems. Users must ensure that the simulated files also have the correct BACKSCAL values, e.g., by reading an appropriate one as both the data and the background into XSPEC before issuing the fakeit command. In some circumstances, the command produces simulated spectra with a BACKSCAL value of 1.0. The value needs to be changed manually (with the fparkey tool, for example) to match the value in the background file used. See the xspec manual for details.
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