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File Descriptions

ASCA distributions have a standard directory structure. This structure is present on ASCA CD-ROM distributions and in the HEASARC ASCA archive. The UK ASCA Archive uses the same basic structure, but with some modifications. Therefore, those accustomed to the layout of the ASCA CD-ROMs are still advised to familiarise themselves the contents of this page.

Below we describe all of the files included in a single ASCA observation, organized by data product type:

  1. UNScreened data files
  2. SCReened data files
  3. Images
  4. AUXiliary products
  5. HTML files

The HEASARC archive for each sequence contains the following additional directories; 'telem', 'spectra', and 'lcurves', not present in the UK ASCA Archive. The 'telem' directory contains the raw information as transmitted on ground. The same information in a suitable format for the ASCA processing software is included in the 'unscreened' directory. The 'spectra' and 'lcurves' directories contain derived files for each detected source. These products can be recreated as they are at HEASARC using the files in the 'screened' directory.


The UNScreened data files

The UNScreened data product contains the unfiltered event files.

Unfiltered Event Files

  • Name: ad[base][bitrate].unf
  • Example: ad10012000g200170h.unf
  • Description: These files contain all of the useful data from the telemetry files in a format readable by ascascreen, the FTOOLS, and xselect. These files contain all of the bad data which must be removed before they will yield scientific results. If you wish to fine-tune the selection criteria for reducing the data (common for in-depth analysis), you should start with these files. For FTOOLS 3.6 or earlier you will need to run ascascreen -e unf to do this. Separate files contain data taken with different instruments, or when the spacecraft was in different states. The event file list gives a descriptive list of each of these files.


The SCReened data files

The SCReened data product contains the filtered event files.

Filtered Event Files

  • Name: ad[base][bitrate].evt
  • Example: ad10012000g200170h.evt
  • Description: These files are the result of passing the unfiltered event files through xselect with a standard set of choices for throwing away bad data. The selection criteria used are described in the processing documentation at HEASARC, and the specific criteria for each file are given in the processing log. The filtered event files are useful for your initial analysis of the data or if you wish to apply stricter selection criteria than those used to create these files. All of the data products in an ASCA distribution are derived from the screened event files.

The Images

Exposure Maps

  • Name: ad[base].totexpo
  • Example: ad51011020gis25670.totexpo
  • Description: An exposure map summed over all the filtered event files and over both instruments of a given type (i.e. both GIS2 and GIS3 or both SIS0 and SIS1). The exposure maps give exposure times in seconds and do not account for vignetting.

Summed Sky Images

  • Name: ad[base]_[all/lo/hi].totsky
  • Example: ad51011020sis32002_hi.totsky
  • Description: Counts image summed in the same way as the exposure maps. These files are divided into three energy ranges:
    • `lo' means <2keV
    • `hi' means >2keV
    • `all' means all energies.

GIF Format Images

  • Name: ad[base].gif
  • Example: ad51011020gis25670.gif
  • Description: Images produced from the `all' energy summed sky images and the exposure maps using ximage. These images have been only minimally smoothed.


The AUXiliary file

This data product contains miscellaneous files produced in processing. The most useful of these are the filter files.

Filter Files

  • Name: ft[date-base].mkf
  • Example: ft930415_2053_0240.mkf
  • Description: A time history of the condition of the spacecraft and instruments. xselect uses this file to filter out bad data from the science files. Filter files are essential for data reduction. There is one filter file for each telemetry file. These are sometimes referred to as "MKF" or "makefilter" files.

Attitude Files

  • Name: fa[date-base]
  • Example: fa930415_2053.0240
  • Description: Files specifying the pointing of the spacecraft as a function of time. You will need these files if you want to run the ascalin FTOOL to recalibrate your data. There is one attitude file for each telemetry file.

Gain History Files

  • Name: ft[date-base].ghf
  • Example: ft930415_2053_0240.ghf
  • Description: A time history of the GIS gain derived from measurements of the detector temperatures. You will need these files if you want to run the ascalin FTOOL to recalibrate your data. There is one gain history file for each telemetry file.

Orbit Files

  • Name: frf.orbit.[version]
  • Example: frf.orbit.160
  • Description File containing the orbital elements for the spacecraft at the time of the observation. Orbit files include information all the way back to the start of the mission, so newer orbit files will work for older observations.

Calibration Source Spectrum

  • Name: ad[base].cal
  • Example: ad51011020g200170.cal
  • Description A PI spectrum extracted from the calibration source in each GIS instrument. A single calibration spectrum is extracted for each combination of energy and spatial binning in the sequence. Usually there is only one spectrum per instrument. These spectra can give a rough check on the GIS gain calibration (the spectrum should peak near 5.9 keV), but note that the gain where the calibration source is located is not as well calibrated as the gain at the center of the detector.


The HTML files

A number of HTML files are generated by the processing, and contain information on everything done to produce the distributed files. The log of errors encountered is especially useful.

Processing Header File

  • Name: ad[sequence]_[ver]_hdr_page.html
  • Example: ad10012000_001_hdr_page.html
  • Description: A basic description of the observation and processing. This is the "home page" for the HTML pages generated in processing.

HTML List of Files

  • Name: ad[sequence]_[ver]_file_info.html
  • Example: ad51011020_056_file_info.html
  • Description: A descriptive list of all the files in the distribution.

Event File List

  • Name: ad[sequence]_[ver]_event_info.html
  • Example: ad51011020_056_event_info.html
  • Description: A descriptive list of all filtered and unfiltered event files. This will answer the question, "How is this event file different from that one?".

Processing Log Index

  • Name: ad[sequence]_[ver]_index.html
  • Example: ad51011020_056_index.html
  • Description: An index to make accessing the processing log easier.

Processing Error Index

  • Name: ad[sequence]_[ver]_errors.html
  • Example: ad51011020_056_errors.html
  • Description: A list of all errors encountered in processing. These are usually checked by the processing team and do not indicate serious problems with the data.

Processing Log

  • Name: ad[sequence]_[ver]_joblog.html
  • Example: ad51011020_056_joblog.html
  • Description: A detailed log of everything done to produce the distributed files. This can be useful for tracking down problems which may have occurred in processing. This log is very verbose, so the processing log index and the processing error index can be helpful for navigating this file.

Source Information

  • Name: ad[sequence]_[ver]_source_info.html
  • Description: Lists the sources detected in the processing for this observation. The quoted counts are the raw counts extracted from a circle not corrected for vignetting or background.


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