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7. Calibration

The instrument teams are responsible for the calibration of instruments, which they will release in the form of documents, software, and calibration files. The latter are released to the public through the calibration database (CALDB; section 7.3). Suzaku GOF is responsible for obtaining the calibration products from the instrument teams and providing them to GOs.

7.1 Documentation

In cooperation with the instrument teams and the OGIP CALDB team, Suzaku GOF will provide a set of documents which describe the Suzaku calibration. These documents should be public and available on-line in text, postscript, pdf or HTML format. At minimum, the document set should cover the following subjects:

7.2 Calibration Software

Calibration software are developed by the instrumental teams, and will be incorporated into the function libraries (section 4), simulation software (section 5.2), and response generators (section 6.5.3). Suzaku GOF will make the calibration softwares conform to the Suzaku software conventions (chapter 3).

When constructing instrumental responses or carrying out instrument specific corrections, it is important that algorithms and parameters be separated as much as possible. The calibration software should not include hardwired parameters, instead reading instrumental parameters from the calibrations files. This ensures that, when parameters are updated by a new calibration, only calibration files need be changed, and will make it possible to test different responses simply by changing parameters.

7.3 Calibration Database (CALDB)

Suzaku calibration files shall be put in the HEASARC Calibration Database (CALDB)7.1, which also contains calibration files for other high energy missions. All the calibration files in CALDB should conform to the OGIP standard FITS format.

7.3.1 Structure and Organization

The master copy of the CALDB is located at GSFC under the anonymous ftp directory, There are two sub-directories, docs and data (for documents and data respectively), and those for a particular mission are stored in docs/[mission] and data/[mission], where [mission] is the mission name. There are instrument directories data/[mission]/[instrument] for each instrument, and each directory contains three sub-directories, pcf, bcf and cpf, which respectively stands for the primary calibration files, basic calibration files and calibration product files.

Primary calibration files are raw or almost-raw calibration data, and will not be directly used to construct instrument responses. Ground calibration data will be archived and regarded as Primary calibration data. Calibration files used to perform instrument specific corrections or to construct responses are called basic calibration files. Responses themselves or calibration files used in the Stage 3 data analysis (section 6.5.4) are called calibration product files.

In the case of ASCA, we did not have primary calibration files. The GIS and SIS teldef files, which carry important instrumental parameters such as dimensions, misalignments and positional gain variations of the sensors, are examples of the basic calibration files. SIS and GIS RMFs are categorized as calibration product files and put under the cpf directory. In the case of Suzaku, we may archive ground calibration data under pcf. Most of the important calibration files listed below (section 7.4) are considered basic calibration files.

7.3.2 Time-Dependent Calibration Files

Some calibration files will be time-dependent. If the variation is long enough ( $\mathrel{\hbox{\rlap{\hbox{\lower4pt\hbox{$\sim$}}}\hbox{$>$}}}$ a few months) and/or the results should be checked by an expert of the instrument, the calibration files may be put in CALDB. The HXD gain history and XIS CTI correction are such calibration data. If the variation is as short as the span of a single observation, the calibration files are created in the pipeline processing although there are no current examples for Suzaku7.2

7.3.3 Calibration File Name

Calibration files should be given unique names to indicate their contents and dates of the release, and a file name and the physical file should have one-to-one correspondence; hence symbolic links should not be used. The calibration files must have the mandatory CALDB keywords which describe the nature of the files and are referenced by CALDB softwares. Recommended naming convention for the Suzaku calibration files is the following:

where inst is the name of the instrument7.3 , kind is brief description of the file contents, and must be less than 8 characters, yyyy, mm and dd are year, month and day of the release, respectively. ext is the file extension, which can be fits or any other letters to describe the nature of the file (e.g., rmf or arf). Both inst and kind should not include hyphens ('-'), underscores or periods ('.').

7.3.4 Version Control

It is essential that the calibration files be under version control and releases be conducted using a well established procedure. Suzaku GOF and instrument teams have established the standard procedure for the delivery and release of calibration files. For each calibration file, there shall be a contact person in the instrument team and in GOF. To avoid confusion, those files are passed through contact persons in GOF and ISAS. After they checked the validity of the file and agreed to release, the file will be shipped to CALDB (Figure 7.1).

Figure 7.1: Delivery of CALDB files between GSFC and ISAS.

CALDB already has an established scheme of the version control. Each instrument directory
has the index file named caldb.indx which contains brief descriptions for all the calibration files included in this directory and the sub-directories. These information are taken from the mandatory CALDB keywords in each calibration file. Also in the caldb.indx file are quality and validity flags of all the calibration files which are to be judged by Suzaku GOF and instrument teams. The CALDB access software, provided by the CALDB team, can choose the appropriate file based on the validity date and other information in caldb.indx.

The identical CALDB tree is mirrored to ISAS regularly, although the primary copy of the CALDB is maintained at GSFC. GOs can obtain and install the entire CALDB on their machines, obtain the subset necessary for their analysis, or remotely access CALDB at GSFC or mirror sites.

7.4 Important Calibration Files

Suzaku GOF and the instrument teams will determine the types of calibration files that are necessary. Important calibration files are listed below.

7.4.1 General

7.4.2 XRT

7.4.3 XIS

7.4.4 HXD

7.5 Suzaku Calibration File Release Plan

  1. Suzaku calibration files may be delivered from ISAS to GSFC on the last working day of each month.

  2. When a new microcode file is made (ae_xis_ucodelst_YYYYMMDD.fits), the file may be implemented into the GSFC and ISAS pipelines immediately, independent of CALDB update. At the end of each month, the new microcode files introduced during the month are delivered to CALDB.

  3. Should there be occasional delays of CALDB file delivery, ISAS shall give advance warning toward GOF.

  4. When calibration files require new tasks or new functionalities, these calibration files must be delivered with the corresponding tasks; namely the delivery may be made on the last working day of January, April, July or October.

  5. When existing files are updated, the format and keywords must not be changed, except for those keywords that are associated with a particular release (FILENAME, VERSION etc).

  6. When new types of the calibration files are created by the instrument teams, their formats and keywords must be agreed to between ISAS and HEASARC before being ingested into the CALDB.

  7. For each delivery of the calibration files, reason of the new delivery and difference from the previous version should be explained.

next up previous contents index
Next: 8. Guest Observer Support Up: Suzaku Project Data Management Previous: 6. Data Analysis and   Contents   Index
Michael Arida 2007-09-29