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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. When reading data from tape, the ascatape FTOOL sets up the standard directory structure automatically.

Below we describe all of the files included in an ASCA distribution, organized by the standard directory in which they reside. The following directories are used for rev2 data:

telem
unscreened
screened
images
spectra
lcurves
aux
calib

The "telem" Directory

This directory contains the telemetry files.

Telemetry Files

Name: ft[date-base]
Example: ft930415_2053.024
Description: The raw information as it was transmitted to the ground. These files contain all the scientific and housekeeping information, but in a hard to read format. There is usually only one telemetry file, but some early observations had two or more. Telemetry files are sometimes called "FRFs" or "First Reduction Files". It is unlikely that you will need the raw telemetry, but it is distributed for completeness.

The "unscreened" Directory

The unscreened directory 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" Directory

The screened directory 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, 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" Directory

This directory contains images and lists of all sources detected in the field of view.

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.

Smoothed, Exposure Corrected Images

Name: ad[base]_[all/lo/hi].smooth
Example: ad51011020gis25670_all.smooth
Description: Images constructed from the summed sky images, and the exposure maps. They have been smoothed with a variable size box-car filter whose size is adjusted so that it smoothes over a minimum of 50 counts. The counts image has been divided by the identically smoothed exposure map. These files are used for source detection in processing.

Source Image

Name: ad[base]_source.ps
Example: ad51011020sis32002_source.ps
Description: A color PostScript format image showing the smoothed, exposure corrected images with energy bands assigned to colors as follows:
- red `lo' ( <2keV )
- blue `hi' ( >2keV )
- green `all' ( all energies )
The images are scaled logarithmically with the brightest pixel in each color receiving full intensity and with 2.5 decades of dynamic range. Celestial coordinates (FK5 J2000) and the extraction regions of all detected sources are overlaid on the image. These images are used as the covers for CD-ROM distributions.

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, so they retain more scientific content than the source images.

Source Catalogs

Name: ad[base].src
Example: ad51011020sis32002.src
Description: FITS BINTABLE listing all of the sources detected in the field of view, with their sky coordinate locations, extraction radii, and a flag for whether they are compact or extended sources.

Source Region Files

Name: ad[base]_[source].reg
Example: ad51011020g225670_0.reg
Description: SAOimage/xselect-style region files used to extract data products for each detected source. These regions are indicated on the source images. Although sources are detected in sky coordinates, these region files are in detector coordinates. The coordinates are converted by extracting events near the source peak in sky coordinates, and calculating their centroid in detector coordinates. Detector coordinates are used in the region files in order to extract spectra for which accurate ARFs may be generated. Note that there is no guarantee that these region files will not include off-detector regions (e.g. interchip gaps or areas excluded by area discriminators). These must be accounted for by following these region filters with other region filters which exclude these areas. Source `0' refers to the entire field of view with all detected sources removed. Spectra and light curves are not extracted for the source `0' regions unless there are no detected sources.

The "spectra" Directory

This directory contains spectra extracted for each source plus response matrices for each spectrum.

PI Spectra

Name: ad[base]_[source].pi
Example: ad51011020g200170_1.pi
Description: Pulse Invariant (PI) spectra readable by xspec. Spectra are extracted for each source from the filtered event files. Data from the event files are combined whenever they would produce a spectrum with the same response matrices. The response matrix keywords (RESPFILE and ANCRFILE) have been set to the corresponding response matrices, but the background keywords (BACKFILE) remain unset. The PI spectra have been grouped to at least 40 events per bin. GIS spectra have been dead-time corrected using the deadtime FTOOL.

Spectrum Plots

Name: ad[base]_[source]_pi.ps
Example: ad51011020g200170_1_pi.ps
Description: PostScript plots of each PI spectrum created with xspec. No background subtraction has been applied to these spectra.

Response Matrix Files

Name: ad[base]_[source].rmf or [instrument][version].rmf
Example: ad51011020s010102_0.rmf -or- gis2v4_0.rmf
Description: Detector response matrix. GIS RMFs are epoch independent and have been fairly stable over the course of the mission. SIS response matrices must be generated for each spectrum, due to aging and surface variation of the CCDs. RMFs are necessary for fitting models to spectra.

Ancillary Response Files

Name: ad[base]_[source].arf
Example: ad51011020g200170_1.arf
Description: The effective area as a function of energy for the x-ray telescopes. ARFs are necessary for fitting models to data.

SIS Area Discriminator Region Files

Name: ad[base]_[source].discrim
Example: ad51011020s010102.discrim
Description: SAOimage/xselect region filters which exclude areas masked off by the SIS area discriminators. These region filters should not remove any data, but they have been used to ensure that the spectra have proper WMAPS for the ascaarf FTOOL.

The "lcurves" Directory

This directory contains light curves extracted for each source from the filtered event files and light curves from ASCA's on-board count-rate monitors.

Binned Light Curves

Name: ad[base]_[source].lc
Example: ad51011020g200070_1.lc
Description: Binned light curves combining data from all filtered event files. The binning is set to give a mean of at least 50 counts per bin but to be no smaller than the coarsest time resolution of the parent event files. GIS light curves have been dead-time corrected using the ldeadtime FTOOL.

Light Curve Plots

Name: ad[base]_[source]_lc.ps
Example: ad51011020g200070_1_lc.ps
Description: PostScript format plots of each binned light curve as produced by xronos. The error bars represent one-sigma Poisson errors.

GIS L1 Count Monitor Light Curves

Name: ft[date-base][G2/G3]HK.lc
Example: ft940408_1555_1729G3HK.lc
Description: Light curves generated from the GIS on-board L1 count rate monitors. These light curves represent counts from the entire visible field of view, but they have a much higher saturation count rate than light curves extracted from events transmitted to the ground. They are therefore useful for very bright objects. One file is extracted from each GIS Housekeeping File. The dead-times for these data are very small and no correction has been made for them.

Unbinned Light Curves

Name: ad[base][bitrate]_[source].ulc
Example: ad51011020g225670h_1.ulc
Description: Event files extracted for each source which may be read by xronos. There is one unbinned light curve for each filtered event file. These files are useful for finer timing analysis than is possible with the binned light curves. Note that no region filtering information is contained in these files, so they should not be used to to extract spectra. Doing so will result in inaccurate ARFs.

The "aux" Directory

This directory 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.

Filter File Plots

Name: ft[date-base]_mkf[c/m/s].ps
Example: ft940408_1555_1729_mkfc.ps
Description: PostScript plots of important quantities in the filter files and the screening criteria applied to create the filtered event files. The characters in the file name extension have the following meanings:
- `c' - Screening criteria common to both SIS and GIS.
- `m' - A time history of the instrument modes
- `s' - Additional screening criteria for SIS instruments.

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.

Dark Frame Error File

Name: ad[sequence]_[s0/s1].dfe
Example: ad34005000_s0.dfe
Description: A table of dark frame error values collected from all faint mode unfiltered event files. The information in this file is also stored in the filter file.

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.

Job Parameter File

Name: ad[sequence]_[ver]_job.par
Example: ad51011020_056_job.par
Description: IRAF/FTOOLS-style parameter file used by processing and containing information specific to this observation.

Processing Parameter File

Name: ad[sequence]_[ver]_process.par
Example: ad51011020_056_process.par
Description: IRAF/FTOOLS-style parameter file used by processing which contains information specific to the processing script version.

Distribution Table of Contents

Name: ad[sequence]_tape.cat
Example: ad10012000_tape.cat
Description: FITS ASCII table listing all the files in the distribution. For tape distributions this file is used by the ascatape FTOOL. All of the information in this file is also contained in the HTML file list.

Housekeeping Files

Name: ft[date-base][S0/S1/G2/G3/CM]HK.fits
Example: ft930415_2053_0240S0HK.fits
Description: Files containing a time history of the spacecraft status. There is one file specific to each instrument (S0, S1, G2, and G3) and one common file for all four instruments (CM). Most of the information contained in these files is in the filter files, so you will probably not need the housekeeping files.

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.

Calibration Source Spectrum

Name: ad[base]_cal.ps
Example: ad51011020g200170_cal.ps
Description A PostScript plot of the calibration source spectrum.

The "calib" Directory

This directory contains all of the calibration files used to process the data. These are not necessarily the best files to use when reprocessing your data. The most recent versions of each of these files can be obtained from the ASCA GOF.

Rigidity Table

Name: rigidity.data.[version]
Example: rigidity.data.1.23
Description: A table used to calculate COR parameter values for the filter file. Low values of the COR parameter imply a higher level of charged particle background.

Leap Second Correction Table

Name: leapsec.fits
Description: Contains a list of leap second events that are used to correct the spacecraft time to actual time for additional conversion (as into UT).

Telescope Calibration Files

Name: [s0/s1]_teldef_ascalin.fits or [gis2/gis3]_ano_[on/off][flf/pow2]_[version].fits
Example: s0_teldef_ascalin.fits gis3_ano_on_flf_180295.fits
Description: Calibration information used by the ascalin FTOOL to convert from raw coordinates to detector coordinates.

CTI Calibration File

Name: sisph2pi_[version].fits
Example: sisph2pi_290296.fits
Description: Calibration file used by ascalin for converting PHA into linearized PI. "CTI" stands for charge transfer inefficiency.

Faintdfe Calibration File

Name: faintdfe.tbl
Description: Calibration file used for calculating SIS dark frame error.

Gain History Calibration File

Name: gis_temp2gain.fits
Description: Calibration file used to create the Gain History File. It contains information describing the long term variation in the GIS gain.

GIS Standard Region Filters

Name: [GIS2/GIS3]_[REGION/CALSRC][pixels].[version]
Example: GIS2_REGION256.3 or GIS2_REGION256_OFF.3
Description: SAOimage/xselect-style region files used to either exclude the GIS calibration sources and noisy outer ring of the detector, or to select the calibration sources. These are used to produce the filtered event files or the calibration source spectra. These filters contain only exclusion regions, so they may be appended to source extraction regions which extend outside of the standard extraction region to extract spectra for which accurate ARFs may be extracted.

SIS Standard Region Filters

Name: [SIS0/SIS1]_OFFCHIP.[version]
Example: SIS0_OFFCHIP.1 or
Description: SAOimage/xselect-style region files which mask off the regions not occupied by any of the four chips in a detector. These will not remove any events, but can be needed for extracting spectra from source regions which are not contained within a single chip.

SIS Chip Mask Region Filters

Name: [SIS0/SIS1]_NOTCHIP[chip].[version]
Example: SIS0_NOTCHIP0.1 or
Description: SAOimage/xselect-style region files which mask off one of the four chips in a detector. These can be used in combination to select data from a single CCD chip, as must be done when generating RMFs for sources which span multiple chips. They may also be used to mask off inactive chips to produce correct WMAPS in spectra. Note that the SIS CCD chips are numbered 0, 1, 2, 3.

Echo Secular History File

Name: sisechos_[version].fits
Example: sisechos_290296.fits
Description: Calibration file used to generate SIS response matrix files.

Residual Dark Distribution History File

Name: sisrddis_[version].fits
Example: sisrddis_290296.fits
Description: Calibration file used to generate SIS response matrix files.

ECD Data File

Name: sis[c0/c1/c2/c3][p40/p20]_[version].fits
Example: sis0c0p40_290296.fits
Description: Calibration file used to generate SIS response matrix files.

X-ray Telescope Effective Area File

Name: xrt_ea_[version].fits
Example: xrt_ea_v1_1.fits
Description: Calibration file used for creating ancillary response files.

X-ray Telescope Point Spread Function File

Name: xrt_psf_[version].fits
Example: xrt_psf_v1_0.fits
Description: Calibration file used for creating ancillary response files.

GIS Beryllium Thickness File

Name: [s2/s3]be[version].fits
Example: s2bev1.fits
Description: Calibration file used for creating GIS ancillary response files.

GIS Grid File

Name: [s2/s3]grid[version].fits
Example: s2gridv3.fits
Description: Calibration file used for creating GIS ancillary response files.

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