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GINGAMODE: Help

GINGAMODE - Ginga LAC Mode Catalog


Overview

The GINGAMODE database table contains selected information from the Large Area Counter (LAC) aboard the third Japanese X-ray astronomy satellite Ginga. The Ginga experiment began on day 36, 5 February 1987 and ended in November 1991. Ginga consisted of the LAC, the all-sky monitor (ASM) and the gamma-ray burst detector (GBD). The satellite was in a circular orbit at 31 degree inclination with apogee 670 km and perigee 510 km, and with a period of 96 minutes.

A Ginga observation consisted of varying numbers of major frames which had lengths of 4, 32, or 128 seconds, depending on the setting of the bitrate. Each GINGAMODE database entry consists of data from the first record of a series of observations having the same values of the following: `BITRATE`, `LACMODE`, `DISCRIMINATOR`, or `ACS MONITOR`. When any of these changed, a new entry was written into GINGAMODE. The other Ginga catalog database, GINGALOG is also a subset of the same LAC dump file used to create GINGAMODE. GINGALOG contains a listing only whenever the `ACS monitor` (Attitude Control System) changes. Thus, GINGAMODE monitors changes in four parameters and GINGALOG is a basic log database mapping the individual FITS files. GINGA FITS files may have more than one entries in the GINGAMODE database. Both databases point to the same archived Flexible Image Transport System (FITS) files created from the LAC dump files. The user is invited to browse though the observations available from GINGA using GINGALOG or GINGAMODE, then extract the FITS files for more detailed analysis. Type `dbhelp/dbname= gingalog` for more information.


Catalog Bibcode

1992Leg.....1...30P

References

The GINGAMODE LAC Catalog was prepared from data sent to NASA GSFC from the Institute of Space and Astronautical Science (ISAS) in Japan. The mission is described by Makino et al. (1987, Astrophys. Letters Commun., 25, 223) and the instrument by Turner et al. (1989, Publ. Astron. Soc. Japan, 41, 345). Some of the present documentation has been adapted from these papers.

Description

The Large Area Counter (LAC) is the main instrument of Ginga. With the large (4000 cm**2) effective area and low internal background, the LAC is the most sensitive detector in the energy range 2-30 keV flown on board an orbiting satellite to date. The LAC consists of eight identical proportional counters each co-aligned and with a 1 X 2 degree field of view (FWHM). It is capable of measuring the energy spectrum of X-ray sources down to 0.2 mCrab level with a nominal energy range from 1.5 to 37 keV. The fractional energy resolution at 6 keV is 18 percent (FWHM) and decreases in proportion to E**-0.5. The whole energy range is divided into 64 energy channels of equal width.

Data Products

This database points to Flexible Image Transport System (FITS) files containing all the Large Area Counter data available at the HEASARC. The FITS files contain low and high channel uncorrected count rates for all LAC observations. These files are essentially lightcurves created from the low and high counts. There are also GIF files for many of the FITS files. There are no GIF files for those FITS files that contain only one point, which represent less than 10% of the total files. There are 11673 FITS files and 10584 GIF files for then entire mission. In this database there can be several entries for each file, since this database maps changes in the major LAC dump parameters.

Parameters

Time
Start time of the interval. The time for the first record of an interval following the change of one of the four basic parameters.

End_Time
Stop time of the interval.

Exposure
Total time on target for the interval. A sum of all the frames for a given time interval.

Acs_Monitor
Designates the spacecraft mode during a particular LAC mode. Settings include: NML (Normal), SL+ (Slewing positive), SL- (Slewing negative), MAN (Maneuver). Slewing is effected by gyroscope and is about the z-axis of the spacecraft which is perpedicular to the pointing direction of the LAC (y-axis). Maneuvering, meaning here a change in the direction of the z-axis, is effected by magnetic torquers and is much slower than slewing.

Bitrate
Rate of telemetered data. L (low), M (medium) or H (high). Bit Rates are: 512 bps (LOW), 2048 bps (MEDIUM) and 16384 bps (HIGH). See `LAC mode` for more information.

Discriminator
Discriminator Setting

Lac_Mode
Spacecraft data modes:

   Mode  PH      Bit Rate                   Note
   ----  ---     ----------                 -----
               High      Medium     Low
               -----     ------     ----
  MPC1   48   500  ms      4  s     16  s   8 detectors by 2 layers
  MPC2   48   62.5 ms    500 ms      2  s   4 detectors combined
  MPC3   12    7.8 ms   62.5 ms    250 ms   8 detectors combined
  PC-H         1.9 ms   15.6 ms   62.5 ms   4 detectors combined
  PC-L        0.98 ms    7.8 ms   31.3 ms   4 detectors combined
  
MPC1 is mainly to study spectra of faint sources. The sixteen spectra (eight detectors, two layers) of the 48 energy channels are output separately.

MPC2 has all 48 energy channels, but, to acheive better temporal resolution, it is compressed by a factor of eight by combining the eight detectors into two groups of four and by combining the two layers.

MPC3 has two layers. 48 energy channels are combined to twelve channels. This improves time resolution by a factor of eight compared with MPC2.

PC-H has signals divided into two energy bands by three discriminators. Dead time is reduced from 206 microsecs to 16.5 microsecs. Maximum time resolution is achieved in this mode.

Skyview
The viewing mode of the spacecraft. The skyview can be SKY (looking away from earth), DYE (Day Earth), NTE (Night Earth), NAT (No Attitude Solution). If there is no attitude solution, there are no corresponding `ra`, `dec`, or `magnetic rigidity` values for the entry.

Name
The name of the spacecraft target based on cross-referencing with previous all-sky surveys including the 4th UHURU, 3rd ARIEL and HEAO A-1 catalogs.

Cindex
Starting Index

Superframe_Number
Major frame number within the observation. This is the mjf for the FIRST record in a GINGAMODE database time interval.

Low_Count_Rate
Average count rate for the low energy channels within this time interval. The Sum of the counts within the interval divided by the integration time for the interval.

High_Count_Rate
Average count rate for the high energy channels within this time interval. The Sum of the counts within the interval divided by the integration time for the interval.

Sud_Count_Rate
Average SUD (Surplus over Upper Discriminator) count rate within this time interval.

Pim_Count_Rate
The PI (Payload Instrument) monitor is the count rate of the V2 guard anodes in anti-coincidence with the other anodes and with the upper level discriminator. Scaled linearly with `SUD count rate`. Averaged over this time interval.

Magnetic_Rigidity
Rigidity of the Earth's magnetic field at the spacecraft. The rigidity for the FIRST record in the interval.

RA
The right ascension of the center of the LAC FOV.

Dec
The declination of the center of the LAC FOV.

LII
The galactic longitude of the center of the LAC FOV.

BII
The galactic latitude of the center of the LAC FOV.

Transmission
The transmission is the collimator efficiency, ideally equal to 1.0. The transmission of the FIRST record in the interval.

No_Of_Records
The total number of records for this interval.

File_Lcurve
The name for the FITS file corresponding to one entry in this database. The FITS files have the form: GYYMMDD_HHMMSS_xz.FITS; G (for GINGA Large Area Counter experiment); the year, month, day, hours, minutes, and seconds of the start of the observation; x, which can be P for pointing, meaning the entire file was 'on-target', S for slewing, or O for other, meaning that standby or no attitude solution occurred in this file); z, which can be 'C' for continuous BITRATE (the value for bitrate within this file is the same for all rows, that is: the timebin size is constant, either 4, 32 or 128 seconds) or 'M' for mixed BITRATE (this file contains one or more bitrates, that is: this file contains rows that vary in length, but the file also contains a TIMEDEL keyword and a FRACEXP (fractional exposure) keyword to normalize the count rates. A typical GINGA FITS file name would be G870305_120455_PC.FITS.


Contact Person

Questions regarding the GINGAMODE database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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