HXD/GSO Background for V2.x Data
| Observation date | Directory | METHOD * | METHODV ** |
|---|---|---|---|
| After 2005-08-17 | gsonxb_ver2.0 | LCFIT (bgd_d) | 2.0ver0711 |
**: FITS header keyword to distinguish the minor revisions of the same model.
This directory is divided into subdirectories by month. For example, background files for observations carried out in 2006 August can be found in the subdirectory 2006_08. Within these monthly directories, individual background files are listed in the order of the sequence number with names like aeNNNNNNNNN_hxd_gsobgd.evt.gz.
Currently, it takes around one month to create the GSO background after the actual observation date. New files for the latest sequences will be uploaded immediately when prepared.
These files should only be used with version 2.x processed data, and vice versa.
Notes
The accuracy of the current background model is as good as <2 % of the averaged background. Observers are strongly recommended to verify the reliability of background, by comparing the model spectrum and light curve with the "earth occultated data" which can be obtained on the condition of ELV<-5. Due to the change of intruementa set-up, the GSO background rate is sometimes significantly different from the model during the period of 2006 March 19 - 2006 May 29. Please check the HXD operation log.
Also, during this period, the data transfer within the instrument sometimes saturated. Please elliminate this period by applying the GTI file generated using hxdgtigen, which can be found in the hxd/hk directory with the name aeNNNNNNNNNhxd_M_tel_uf.gti.
A correct gain calibration is essential in estimating the background accurately. Unfortunately, it has been found that the GSO gain correction using the current version of hxdpi shows a small discontinuity around 2006 March 3 - 2006 May 9; the energy scale of reprocessed data becomes different by several % from that of response and background. HXD team is now developing the new version hxdpi so as to resolve this problem.
For further details of the status of current HXD/GSO background model for v2 products, please refer to Suzaku Memo 2008-01.
Scripts for GSO Analysis
Added on 2009 Dec 4: two new scripts, hxdgsoxbpi and hxdgsoxblc, allow users to create the source(+background) and background spectra/light curves in one step. These scripts have been released as part of Suzaku FTOOLS V14 in HEAsoft V6.8.
Usage
The usage of GSO event and background files is similar to that of the PIN data. Here we note some key differences.
- The event rate of the GSO background files has not been artifitially
inflated by a factor of 10 (unlike those of the PIN background files).
Therefore, the users need not, and should not, modify the exposure time.
- All GSO event files must be
reprocessed
- Users must correct the dead time of the GSO background spectral files
as well as the observed spectral file.
- The background event files do not include the Cosmic X-ray Background.
However, the CXB is less than 0.1% of the total background rate in
the GSO, and thus it is negligible.
- Since the GSO background is created in 32 bins as listed
below, the source spectrum must also be rebinned
using gso_grp.dat
in grppha (Note but this binning
scheme applies only to the old GSO gain calibration; for the new
benning scheme, see our
page on the new GSO gain calibration).
grppha> group gso_grp.dat
Binning of GSO spectra, in the interactive syntax in grppha
group 0 24 25 25 26 2 27 28 2 29 31 3 32 35 4 36 38 3 group 39 42 4 43 46 4 47 51 5 52 56 5 57 62 6 group 63 68 6 69 75 7 76 83 8 84 91 8 92 100 9 group 101 110 10 111 121 11 122 134 13 135 147 13 148 162 15 group 163 178 16 179 196 18 197 216 20 217 238 22 239 262 24 group 263 288 26 289 317 29 318 349 32 350 384 35 385 422 38 group 423 465 43 466 511 46The same information is contained in gso_grp.dat.
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