XIS Night Earth background Files: Cycle 4 Versions
NXB files for diffuse emission ("Entire field of view") contained an incorrect value (1.0) of the "BACKSCAL" keyword (see bottom of the page for an explanation), and were replced by new files on 2008 Dec 1. Please download again if you have already obtained old NXB files and plan to use the "Entire Field of View" versions.
The XIS team has released a set of night earth background files for the preparation of AO-4 proposals. The spaced-raw charge injection (SCI), which is used by default in AO4, reduces the effective area of XIS by 5.6%. Although this effect is not included in the night earth background files released here, it is negligible for the purpose of simulation. Please refer to the AO2 page for details of the night earth data used here.
A gzipped tar file is available for download, containing the following 12 files.
- XIS nominal position (r=6mm)
- Sky coordinate
- nte_xisBI_xispos_6mm_sky.pi (XIS1)
- nte_xisFI_xispos_6mm_sky.pi (sum of XIS0 and XIS3)
- Detector coordinate
- nte_xisBI_xispos_6mm_det.pi (XIS1)
- nte_xisFI_xispos_6mm_det.pi (sum of XIS0 and XIS3)
- HXD nominal position (r=6mm)
- Sky coordinate
- nte_xisBI_hxdpos_6mm_sky.pi (XIS1)
- nte_xisFI_hxdpos_6mm_sky.pi (sum of XIS0 and XIS3)
- Detector coordinate
- nte_xisBI_hxdpos_6mm_det.pi (XIS1)
- nte_xisFI_hxdpos_6mm_det.pi (sum of XIS0 and XIS3)
- Entire XIS FOV (Updated 2008 Dec 1)
- Sky coordinate
- nte_xisBI_entireFOV_sky.pi (XIS1)
- nte_xisFI_entireFOV_sky.pi (sum of XIS0 and XIS3)
- Detector coordinate
- nte_xisBI_entireFOV_det.pi (XIS1)
- nte_xisFI_entireFOV_det.pi (sum of XIS0 and XIS3)
These files can be used simulation purpose only. Please use with a matching set of RMF and ARF files.
A second gzipped tar file (also updated on 2008 Dec 1) contains a set of 12 files that have been reduced in size using a variable rebinning scheme. These should be used with the corresponding RSP files.
Note on BACKSCAL: With the Dec 1 updates, the XIS Night Earth spectra have the correct values of the BACKSCAL keyword, which is the area of the "extraction region" as a fraction of the total area of that coordinate system (1024 x 1024 for Detector, and 1536 x 1536 for SKy, coordinates). XSPEC uses the ratio of EXPOSURE x BACKSCAL to scale the background file before subtracting it from the data file. On the other hand, the "fakeit" copies the BACKSCAL from an existing data file (if one has been read in) or uses the default value of 1.0. Users must ensure that the simulated file has the correct BACKSCAL value, or that the simulated data and background files have a consistent set of BACKSCAL values.
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