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Last modified: 26 October 2016

URL: http://cxc.harvard.edu/ciao/data_products_guide/time.html

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

Data Products Guide

Filename Description Content SDP Pipeline
acis_flt1.fits good time intervals GTI ACIS1
hrc_std_flt1.fits good time intervals GTI HRC1
acis_mtl1.fits mission timeline MTL ACIS1
hrc_mtl1.fits mission timeline MTL HRC1
hrc_dtf1.fits HRC dead time factor DTFSTATS HRC1

Good Time Intervals

Filename Description Content SDP Pipeline
acis_flt1.fits good time intervals GTI ACIS1
hrc_std_flt1.fits good time intervals GTI HRC1

Description:

The GTI 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" are periods when observing conditions were good; they fall between the TSTART and TSTOP. The two principal causes of a 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.

Creator pipeline: acis_L1

dmgti - GTIs are built on a per-chip basis in the pipeline.

GTI-specific columns:

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

Mission Timeline

Filename Description Content SDP Pipeline
acis_mtl1.fits mission timeline MTL ACIS1
hrc_mtl1.fits mission timeline MTL HRC1

Description:

The mission timeline (MTL) file contains the telescope's housekeeping and configuration information, such as pointing relative to the sun's limb, particle flux, aspection solution status, and grating position. For HRC files, voltage monitors and image diagnostics are also included.

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 creating the GTIs.

Creator pipeline: acis_L1

The MTL tool, mtl_build_table, is not distributed with the CIAO software.

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 - (HRC) Imaging Bot MCP HV Monitor
IMHBLV - (HRC) Imaging Bot & TOP MCP HV Monitor
SPHVLV - (HRC) Spect Bot MCP HV Monitor
SPHBLV - (HRC) 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 -
THR_PIX - (ACIS)
EVTSENT - (ACIS)
EXPNO - (ACIS)
DETNAM - -
DATAMODE - -
READMODE - (ACIS)
FP_TEMP - -
GRATING - -
DET_HV - (HRC) High Voltage ON or OFF
MOVING - Is SIM moving?
DTF - (HRC)
AOFF_GAP - Aspect offset gap? 0=no 1=gap
ASPTYPE - Solution method
COUNT_RATE count/second Count Rate

HRC Dead Time Factor

Filename Description Content SDP Pipeline
hrc_dtf1.fits HRC dead time factor DTFSTATS HRC1

Description:

The dead time correction factors as a function of time. For ACIS observations, the dead time correction is recorded in the DTCOR header keyword. Since the HRC dead time correction factor varies during the observation, however, the value of DTCOR represents an average and the individual values are stored in the dtf1.fits file.

Creator tool: hrc_calc_dead_time

DTF-specific columns:

Column Name Units
TIME s
DTF
DTF_ERR
PROC_EVT_COUNT count
TOTAL_EVT_COUNT count
VALID_EVT_COUNT count
STATUS

Last modified: 26 October 2016
Smithsonian Institute Smithsonian Institute

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