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NOTICE:This Legacy journal article was published in Volume 1, May 1992, and has not been updated since publication. Please use the search facility above to find regularly-updated information about this topic elsewhere on the HEASARC site. |
New Ginga Catalogs
Brendan Perry
HEASARC
Instrument
Two recent additions to the HEASARC database come from the Japanese X-ray satellite, Ginga, formerly known as ASTRO-C. These new catalogs, Gingalog and Gingamode, have been created from the Large Area Counter (LAC) experiment data files and are available to on-line users of the HEASARC database via the BROWSE software. The LAC was the main instrument aboard GINGA and its 4000 cm2 detector up to now has been one of the most sensitive in the energy range from 2-30 keV. It was capable of measuring the energy spectrum of X-ray sources down to 0.2 millicrab and it operated successfully from 5 February 1987 until 1 November 1991.
The LAC data files are records of all the LAC observations and contain uncorrected broad band count rates in one of three telemetry time intervals. Thus, the instrument's 48 pulse height channels were summed into two channels that were written into the LAC data files as LACLOW and LACHIGH. These energy channel values were then written out in ASCII records either every 4, 32, or 128 seconds depending on the instrument's telemetry bitrate, which can be high, medium, or low respectively. These ASCII records were then read into two separate catalogs within the HEASARC metabase and into FITS files. The new catalogs can be accessed to ascertain what archival Ginga data exists. Anyone wishing to analyze or gain access to the background-subtracted, higher time resolution data must contact Dr. F. Makino at ISAS in Japan. This article describes how the HEASARC catalogs Gingalog and Gingamode were created from the LAC data files.
Gingalog
The large LAC data files were divided into two catalogs that only indicated when changes occurred in the LAC data file records. In Gingalog, each time one of the parameters, the Attitude Control System Monitor (ACS Monitor), changed from its previous value, a new entry was written to the Gingalog catalog. Since Gingalog was meant only as a log, only certain parameters from the original LAC data file were written to the catalog. These parameters include:
Target Name
RA and DEC
LII and BII
Start and Stop time
Z Axis RA and Z Axis DEC
ACS Monitor
The ACS Monitor parameter was selected because it defines the spacecraft pointing mode, and has values of:
NML normal SL+ slewing positive SL- slewing negative MAN maneuver S36 slew through 360 degrees STB standby LSP low spin
Gingamode
The Gingamode catalog is a log of each change in the instrument mode. Gingamode was also created by reading the LAC data file and a new entry to Gingamode was written when any of the BITRATE, LAC MODE, ACS MONITOR or DISCRIMINATORS parameters changed. Unlike Gingalog, Gingamode contains all the same parameters as the original LAC data files so it has all the parameters that Gingalog has, plus those in the FITS files mentioned above.
FITS Files
Since Gingalog contains only records when the ACS Monitor value changed, those records occurring between changes were written into FITS format data files stored on an NDADS optical WORM platter. There is one FITS file per entry in Gingalog. They are also accessible using BROWSE when Gingalog is loaded. They can be plotted by the PLOTFITS command or extract using the FSTAGE and xp commands. The first record in one of the FITS files will also be an entry in the Gingalog catalog, and the remaining records will be all the original LAC data file records after that one having the same ACS Monitor value. Since the records within the original LAC data files were separated by either 4, 32 or 128 seconds depending on the bitrate, the time resolution within a FITS file will vary because the start time of a record will only be known to one of the above three accuracies. The FITS files also contain all the parameters from the original LAC data files not included in the Gingalog entries. These parameters include:
BITRATE rate of telemetered data LAC MODE spacecraft data mode DISCRIMINATORS setting of the three discriminators SKYVIEW spacecraft viewing mode SUPER FRAME NUMBER major frame within an observation LOW COUNT RATE lower channels count rate HIGH COUNT RATE higher channels count rate SUD COUNT RATE surplus over the upper level discriminator PIM COUNT RATE payload instrument monitor count rate MAGNETIC RIGIDITY earth's magnetic field rigidity TRANSMISSION collimator efficiencyThe on-line user can view the entries in Gingalog, and if there is a section of data that the user would like to scrutinize further, the FITS file corresponding to that section can be accessed and analyzed. Thus the user has access to all the data without the time consuming search by BROWSE through the millions of records in the original LAC dump files.
Both catalogs point to FITS files. Each Gingalog entry will have one FITS file but there can be several Gingamode entries corresponding to each FITS file because a new FITS file will only be created when the ACS Monitor value changes. Thus, either catalog can be scanned for changes in count rates or other parameters and any entry that looks interesting can be further studied by accessing the corresponding FITS file and seeing all the observation frames that succeeded it. The FITS file name corresponding to each Gingalog or Gingamode entry is shown in the LAC FILE parameter listed in either catalog. Questions and comments concerning these catalogs, or requests for individual FITS files can be addressed to Brendan Perry (HEASRC::PERRY) or Charles Day (HEASRC::DAY).
An example of BROWSE sessions with Gingalog and Gingamode appears on the following page.
Gingalog and Gingamode Examples from BROWSE
HEASARC> browse gingalog Loading GINGALOG database sample TOTAL indexed on DEC Ginga LAC Log Catalog GINGALOG_TOTAL_DEC > sc Search in a cone of selected R.A. (1950 d/f= 5 h 36 m 19.20sec): 5 30 radius centered on selected Dec (1950 d/f=-72 deg 34 m 12.00sec): -68 00 coordinates. Radius in arcmin. (d/f= 60.00):45.00 GINGALOG_TOTAL_DEC > dsam Display the database parameters on one line. GINGALOG_TOTAL_DEC > dall Display all the parameters of Enter start entry number [d/f=1]: 1 selected entries. Enter end entry number [d/f=1]: GINGALOG_TOTAL_DEC > dcoord Display name and coordinates Enter start entry number [d/f=1]:3 of selected entries Enter end entry number [d/f=1]:8 GINGALOG_TOTAL_DEC > cdb Change databases to Gingamode. Database name: gingamode Loading GINGAMODE database sample TOTAL indexed on DEC Ginga LAC Mode Catalog GINGAMOD_TOTAL_DEC > sc Search in a cone of selected R.A. (1950 d/f= 5 h 30 m 00.00sec): 5 30 radius centered on selected Dec (1950 d/f=-68 deg 00 m 00.00sec): -68 00 coordinates. Radius in arcmin. (d/f= 60.00):45.00 GINGAMOD_TOTAL_DEC > dsam Display the database parameters on one line. GINGAMOD_TOTAL_DEC 6> exit Exit BROWSE.

