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Suzaku Guest Observer Facility

HXD/GSO Background for V2.x Data


New HXD/GSO background files corresponding to the new version of hxdpi (HEAsoft v6.9 and later) are now available.

Observation date Directory METHOD * METHODV ** gptfile_date
2005-08-17 to 2011-11-03*** gsonxb_ver2.5 LCFIT (bgd_d) 2.5ver0912-64 20100323
After 2011-03-01 gsonxb_ver2.6 LCFIT (bgd_d) 2.6ver1110-64 20110819
*: FITS header keyword to distinguish the background modeling methods.
**: FITS header keyword to distinguish the minor revisions of the same model.
***Version 2.6 should be used for observations taken between 2010-03-01 and 2011-11-03 if it has been reprocessed with the latest gsogpt file.

You should choose ver2.5 or ver2.6, according to the GSO energy calibration file ae_hxd_gsogpt_20100323.fits or ae_hxd_gsogpt_20110819.fits used in the processing. The pipe-line processing uses ae_hxd_gsogpt_20100323.fits before 2011 Nov 3 data and ae_hxd_gsogpt_20110819.fits after 2011 Nov 3 data. You can check which gsogpt file is used for your data and background in the processing by the header keyword GSOGPT_F.

By default, users do not have to reprocess the GSO data. Since the difference between the analysis results between the two gsogpt files is not large. Only for bright sources (above 100 mCrab in the GSO band), we recommend to reprocess the data from 2010 Mar 1 to 2011 Nov 3. Once you reprocess the data with ae_hxd_gsogpt_20110819.fits, you should use the background ver 2.6. This is also the case when you use the tool aepipeline which automatically choose the newest calibration file, ae_hxd_gsogpt_20110819.fits.

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 data processed with Suzaku software version 16 (Heasoft v6.9) or later.


The status of current HXD/GSO background model for version 2 products is described in Suzaku Memo 2008-01.

Ratio of observed bgd and model


The usage of GSO event and background files is similar to that of the PIN data. Here we note some key differences.

  1. 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.

  2. All GSO event files must be reprocessed

  3. Users must correct the dead time of the GSO background spectral files as well as the observed spectral file.

  4. 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.

  5. 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 46
The same information is contained in gso_grp.dat.

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This file was last modified on Tuesday, 10-Apr-2012 19:16:57 EDT

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