GINGAMODE - Ginga LAC Mode Catalog
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.
The Ginga 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.
Start time of the interval. The time for the first record of an interval following the change of one of the four basic parameters.
Stop time of the interval.
Total time on target for the interval. A sum of all the frames for a given time interval.
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.
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.
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 combinedMPC1 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.
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.
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.
Major frame number within the observation. This is the mjf for the FIRST record in a GINGAMODE database time interval.
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.
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.
Average SUD (Surplus over Upper Discriminator) count rate within this time interval.
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.
Rigidity of the Earth's magnetic field at the spacecraft. The rigidity for the FIRST record in the interval.
The right ascension of the center of the LAC FOV.
The declination of the center of the LAC FOV.
The galactic longitude of the center of the LAC FOV.
The galactic latitude of the center of the LAC FOV.
The transmission is the collimator efficiency, ideally equal to 1.0. The transmission of the FIRST record in the interval.
The total number of records for this interval.
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.