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Last modified: 28 October 2009

URL: http://cxc.harvard.edu/ciao4.2/data_products_guide/gti_descrip.html

Good Time Intervals (GTI)
and the Mission Timeline (MTL)

Data Products Guide

Level Instrum Data product Content Pipeline Filename template
L1 ACIS ACIS Good Time Interval GTI ACIS1 flt1.fits
L1 ACIS ACIS Mission Timeline MTL ACIS1 mtl1.fits
L1 HRC HRC Good Time Interval GTI HRC1 std_flt1.fits
L1 HRC HRC Mission Timeline MTL HRC1 mtl1.fits

ACIS Good Time Interval (GTI)

Level Instrum Data product Content Pipeline Filename template
L1 ACIS ACIS Good Time Interval GTI ACIS1 flt1.fits

description:

This file contains the start and stop times of all accepted time intervals over the observation. This L1 product is used to filter the L1 events at the start of L2 in order to determine the standard set of photons for the observation. It is the photons that pass this time filter that are further processed in L2. When the event file is filtered, the GTI filter is also merged with the time subsection extension of the event list as a dynamic record of the current set of time filters applied to the data.

The "good times", between TSTART and TSTOP, are periods when observing conditions were good. The two principal causes of bad observing period are: (1) bad aspect solution, and (2) high background. Users may wish to create a more restrictive set of GTIs if they require a very low background (e.g. for extended source analysis). The tool dmgti can be used for this. See the CIAO threads page for more information.

file name:

GTI information is typically contained in the MTL or event files. It is not distributed as an independent data product. Look for GTI blocks (one per chip) in files whose names contain: 'evt', 'mtl1', 'img2', or 'flt1'.

creator pipeline:

ACIS L1

creator tool:

dmgti - GTIs are built on a 'per chip' basis. The GTI blocks are then attached to certain other data products, as noted above.

useful links:

GTI specific columns:

Column Name Units Description
START seconds Good time interval start time
STOP seconds Good time interval stoptime

ACIS Mission Timeline (MTL)

Level Instrum Data product Content Pipeline Filename template
L1 ACIS ACIS Mission Timeline MTL ACIS1 mtl1.fits

description:

This file contains the telescope's housekeeping and configuration information. The contents of the MTL are specified by a lookup table which is determined by science input. The MTL also defines good observing times, which is used (in part) to create the GTIs.

Important parameters include: pointing relative to the sun's limb, particle flux, aspection solution status, grating position, etc.

file name:

*_mtl1.fits

creator pipeline:

acis_L1

creator tool:

mtl_build_table

MTL specific columns:

Column Name Units Description
time seconds -
Point_SunLimbAng degrees Pointing angle from Solar Limb
Point_MoonLimbAng degrees Pointing angle from Lunar Limb
Point_EarthLimbAng degrees Pointing angle from Earth Limb
Point_RamVectorAng degrees Pointing-Ram angle
Dist_SatEarth meters Satellite-Earth distance (from Earth center)
SCP4 Hz/cm**2/sr Sci coincidence counter P4 rate
SCP8 Hz/cm**2/sr Sci coincidence counter P8 rate
SCH4 Hz/cm**2/sr Sci coincidence counter H4 rate
SCH8 Hz/cm**2/sr Sci coincidence counter H8 rate
SCE150 Hz/cm**2/sr Sci coincidence counter E150 rate
SCE300 Hz/cm**2/sr Sci coincidence counter E300 rate
SCE1300 Hz/cm**2/sr Sci coincidence counter E1300 rate
SCE3000 Hz/cm**2/sr Sci coincidence counter E3000 rate
SCINT Hz/cm**2/sr Sci coincidence counter INT rate
SCP25 Hz/cm**2/sr Sci coincidence counter P25 rate
SCP41 Hz/cm**2/sr Sci coincidence counter P41 rate
SCH25 Hz/cm**2/sr Sci coincidence counter H25 rate
SCH41 Hz/cm**2/sr Sci coincidence counter H41 rate
HRMA_CAPGRAD0 K -
HRMA_CAPGRAD1 K -
HRMA_CAPTEMP K -
HRMA_FRWDTEMP K -
HRMA_AFTTEMP K -
HRMA_TEMP K -
OBA_PERIGRAD0 K -
OBA_PERIGRAD1 K -
THR_PIX - -
EVTSENT - -
DETNAM - -
DATAMODE - -
READMODE - -
FP_TEMP - -
GRATING - -

HRC Good Time Interval (GTI)

Level Instrum Data product Content Pipeline Filename template
L1 HRC HRC Good Time Interval GTI HRC1 std_flt1.fits

For more detailed information, see the ACIS GTI section.

creator pipeline:

HRC L1

creator tool:

dmgti - GTIs are built on a 'per chip' basis. The GTI blocks are then attached to certain other data products, noted above.

GTI specific columns:

Column Name Units Description
START seconds Good time interval start time
STOP seconds Good time interval stoptime

HRC Mission Timeline (MTL)

Level Instrum Data product Content Pipeline Filename template
L1 HRC HRC Mission Timeline MTL HRC1 mtl1.fits

For more detailed information, see the ACIS MTL section.

description:

The HRC MTL file contains nearly identical information to the ACIS MTL file. HRC-specific parameters include: voltage monitors and image diagnostics.

file name:

*_mtl1.fits

creator pipeline:

HRC L1

creator tool:

mtl_build_table

MTL specific columns:

Column Name Units Description
time seconds -
Point_SunLimbAng degrees Pointing angle from Solar Limb
Point_MoonLimbAng degrees Pointing angle from Lunar Limb
Point_EarthLimbAng degrees Pointing angle from Earth Limb
Point_RamVectorAng degrees Pointing-Ram angle
Dist_SatEarth meters Satellite-Earth distance (from Earth center)
SCP4 Hz/cm**2/sr Sci coincidence counter P4 rate
SCP8 Hz/cm**2/sr Sci coincidence counter P8 rate
SCH4 Hz/cm**2/sr Sci coincidence counter H4 rate
SCH8 Hz/cm**2/sr Sci coincidence counter H8 rate
SCE150 Hz/cm**2/sr Sci coincidence counter E150 rate
SCE300 Hz/cm**2/sr Sci coincidence counter E300 rate
SCE1300 Hz/cm**2/sr Sci coincidence counter E1300 rate
SCE3000 Hz/cm**2/sr Sci coincidence counter E3000 rate
SCINT Hz/cm**2/sr Sci coincidence counter INT rate
SCP25 Hz/cm**2/sr Sci coincidence counter P25 rate
SCP41 Hz/cm**2/sr Sci coincidence counter P41 rate
SCH25 Hz/cm**2/sr Sci coincidence counter H25 rate
SCH41 Hz/cm**2/sr Sci coincidence counter H41 rate
IMHVLV - Imaging Bot MCP HV Monitor
IMHBLV - Imaging Bot & TOP MCP HV Monitor
SPHVLV - Spect Bot MCP HV Monitor
SPHBLV - Spect Bot & Top MCP HV Monitor
img_diam_rms arcsec Aspect image RMS diameter
img_roll_rms arcsec Aspect image RMS roll err
target_offset arcsec Target offset from nominal
rw_speed_bad - Reaction wheel speed bad
asp_sol_status - Aspect solution quality
HRMA_CAPGRAD0 K -
HRMA_CAPGRAD1 K -
HRMA_CAPTEMP K -
HRMA_FRWDTEMP K -
HRMA_AFTTEMP K -
HRMA_TEMP K -
OBA_PERIGRAD0 K -
OBA_PERIGRAD1 K -
GRATING - -
DETNAM - HRC detector name
DET_HV - High Voltage ON or OFF
DATAMODE - -
MOVING - -
STATUS - -
DTF - -
AOFF_GAP - Aspect offset gap? 0=no 1=gap
ASPTYPE - Solution method
RATE count/second Count Rate

Last modified: 28 October 2009