New Gain Calibration of the GSO Data

Updated 2012 June 8

The HXD team has released a set of new software and calibration files that impliments a revised gain calibration of the HXD/GSO data. This extends the low energy limit of the usable GSO data from 70 keV down to 50 keV. A more detailed description of the new calibration will be published elsewhere.

For data taken on or before 2010 February 28, there are two options:
1. Reprocess the data with the new gain calibration (recommended).
  - In this case, users must use the background files created using the new gain calibration, as well as the matching response file.
2. Continue using the data processed with the old gain calibration (recommended only for the purpose of comparing new data with previously analyzed data using the same calibration),
  - In this case, users must use the background files created using the old gain calibration, as well as the matching response file. See the "Backward Compatibility" section below.
For data taken on or after 2010 March 1, users must use the new gain calibration, since no background files will be produced with the old gain calibration for these observations.
- GSO data must be (re)processed with the new software before use.
- In 2011 September, The HXD team released an updated gain history file for the GSO that reduces gain fluctuation for data taken since 2010 March. For data taken between 2010 March 1 and 2011 November 3, reprocessing may be advantageous. See this page for further information.

1. Calibration Files (HXD CALDB 20100617 Release)

The new release includes

A new type of GSO gain history files, ae_hxd_gsogpt_YYYYMMDD.fits, which replaces the GHT type gain history files. The GPT files have a longer period of validity, and updates are expected every three months.
A new version of the pulse shape discrimination file, ae_hxd_gsopsd_20090812.fits. This file has the CALDB keyword CCNM0001 set to PSDSEL2 and must be used with the new GSO calibration.
(Updated 2010 July 2): A new pair of respone files, to be used with the new calibration:
- ae_hxd_gsohxnom_20100524.rsp
- ae_hxd_gsoxinom_20100524.rsp
Note that the 20100107 versions, the original release for the new GSO gain calibration, have an error in that the energies of the PI channels are shifted by 1 keV. Note also that, starting with the 20100524 versions, the GSO response files for the new gain calibrations will have a new keyword, GSOOLDPI, with the value set to F. The responses corresonding to the old gain calibration (as well as the 20100107 versions for the new gain) do not contain the GSOOLDPI keyword.
The HXD team has released a new set of empirical efficiency correction files to go along with the new calibration. Without the new correction files, the GSO data can be analyzed but systematic errors of about 15% remain in the 50-70 keV band.
For data processed with the old GSO calibration, users must continue to use:
- ae_hxd_gsoxinom_20080129.rsp
- ae_hxd_gsohxnom_20080129.rsp
and are encouraged to combine these with the empirical efficiency correction files

2. Software (HEAsoft 6.9, 2010 March 29 Release)

The new release includes updated versions of hxdpi and hxdgrade.

The tool hxdpi uses the new type GSO gain history file, ae_hxd_gsogpt_YYYYMMDD.fits and no longer supports the old GSO gain files (ae_hxd_gsoght_YYYYMMDD.fits).
Event files processed with this version of hxdpi will have in the header a new keyword GSOOLDPI set to F to mark that the new GSO calibration has been applied.
The tool hxdgrade uses the GSOOLDPI keyword to select the correct pulse shape discrimination file from the CALDB (e.g. ae_hxd_gsopsd_20090812.fits for the new GSO calibration gain). If the keyword is not present, it assumes that the event were processed with the old GSO calibration.

3. Processing

The processing pipelines have been updated to use the new software and calibration files, as of pipeline version 2.5.16.28 (V2.4.12.27 is the last version of the piepeline that used old GSO gain calibration). Processing with the new GSO calibration has started for data taken on or after 2010 March 21, including all Cycle 5 observations.

4. Background Files (Updated 2012 Jun 8)

The GSO non X-ray background files with the new gain are available at: ftp://heasarc.gsfc.nasa.gov/suzaku/data/background/gsonxb_ver2.5 or ftp://heasarc.gsfc.nasa.gov/suzaku/data/background/gsonxb_ver2.6/ divided into monthly subdirectories. See Version 2.6 release notes for an explanation of which version should be used.

5. Usage (New on 2010 Apr 6)

There are two important differences in how users should analyze the GSO data with the new calibration, beyond acquiring the appropriate set of software, calibration files (including the response), and the background file.

Users should check the GSOGPT_F and GSOGPT_V keywords in the FITS headers of the event (observed) and the background (simulated) files. If these keyword values match, then there is no need to reprocess the GSO data. It is anticipated that, once processing starts with the new gain calibration, this will often be the case even for newly obtained and processed observations. If the values of these keywords differ between the data and the background files, users must reprocess their data.
- An exception to this rule is that the files ae_hxd_gsogpt_20091225.fits and ae_hxd_gsogpt_20100323.fits are identical in content, differing only in a CALDB keyword. If the background file is created with one of the two and the event file is procesesed with the other, there is no need to reprocess the data.

The new GSO background files are created using a new grouping with 64 bins as follows, in the interactive syntax in grppha:

group 0 24 25 25 26 2 27 27 1 28 28 1 29 30 2 31 31 1
group 32 33 2 34 35 2 36 36 1 37 38 2 39 40 2 41 42 2
group 43 44 2 45 46 2 47 49 3 50 51 2 52 54 3 55 56 2
group 57 59 3 60 62 3 63 65 3 66 68 3 69 71 3 72 75 4
group 76 79 4 80 83 4 84 87 4 88 91 4 92 95 4 96 100 5
group 101 105 5 106 110 5 111 116 6 117 121 5
group 122 127 6 128 134 7 135 140 6 141 147 7
group 148 154 7 155 162 8 163 170 8 171 178 8
group 179 187 9 188 196 9 197 206 10 207 216 10
group 217 227 11 228 238 11 239 249 11 250 262 13
group 263 274 12 275 288 14 289 302 14 303 317 15
group 318 332 15 333 349 17 350 366 17 367 384 18
group 385 403 19 404 422 19 423 443 21 444 465 22
group 466 487 22 488 511 24

Users should apply the same channel grouping to their data. Most conveniently, after extracting the spectrum, this can be done in grppha using the command:

grppha> group gsobgd64bins.dat

after saving the file gsobgd64bins.dat.

6. Backward Compatibility

To maintain backward compatibility, the following steps have been taken.

The old version of hxdpi is available in the new release, under the name hxdpi_old, to enable reprocessing of data using the old calibration. This is based on the version of hxdpi available in HEAsoft 6.8, but now writes the new keyword GSOOLDPI set to T to indicate that the old GSO calibration has been applied.
hxdgrade uses the GSOOLDPI keyword to select the correct pulse shape discrimination file from the CALDB (e.g. ae_hxd_gsopsd_20071010.fits for the old GSO gain calibration). If the keyword is not present it assumes that the event were processed with the old GSO calibration.
The background files for the old GSO calibration will continue to be available at ftp://heasarc.gsfc.nasa.gov/suzaku/data/background/gsonxb_ver2.0 for observations obtained on 2010 February 28 or earlier.
The script aepipeline allows to reprocess data with both the old and new GSO gain calibration via the parameter hxdpi_old, which is set to no by default.

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This file was last modified on Wednesday, 20-Oct-2021 08:36:54 EDT