XIS Non X-ray background Files: Cycle 10 Versions
The XIS team has released a set of non X-ray background (NXB) files suitable for the preparation of AO-10 proposals.
The NXB spectra were extracted from a circular region of a radius of 6 mm centered at the XIS nominal position. Because the unit of the BACKSCAL keyword changes with the coordinate system, the spectra were created for both the DET and SKY coordinates.
The XIS team also prepared the NXB spectra for the entire filed of view. In this case, users should note that regions irradiated by the onboard calibration sources were excluded.
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. Note that the spectra for the FI sensor are summed, not averaged.
An exposure times of 400 ks is assumed, to match the default length (+/-150 days of the observation date) in the nxbgen tool.
The loss of the detector area by the calibration source masking, dead rows due to the spaced-row charge injection, and the permanent area discrimination of a part of the XIS0 are taken into account.
A gzipped tar file is available for download, containing the following 8 files.
- XIS nominal position (r=6mm)
- Sky coordinates
- XIS_BI_NXB_xisnom_sky.pi (XIS1)
- XIS_FI_NXB_xisnom_sky.pi (sum of XIS0 and XIS3)
- Detector coordinates
- XIS_BI_NXB_xisnom_det.pi (XIS1)
- XIS_FI_NXB_xisnom_det.pi (sum of XIS0 and XIS3)
- Entire XIS FOV
- Sky coordinates
- XIS_BI_NXB_entireFOV_sky.pi (XIS1)
- XIS_FI_NXB_entireFOV_sky.pi (sum of XIS0 and XIS3)
- Detector coordinates
- XIS_BI_NXB_entireFOV_det.pi (XIS1)
- XIS_FI_NXB_entireFOV_det.pi (sum of XIS0 and XIS3)
These files (either the sky or detector coordinate versions) files are suitable for simulation purposes only.
Note that these files have 4096 channels. Please use with a matching set of RMF and ARF files.
2048 channel versions
A second gzipped tar file contains a set of 12 files that have been rebinned using a variable rebinning scheme into 2048 channels. These should be used with the corresponding RSP files.
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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