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 efficiency 

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. 

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