CalDB 4.8.3.1 Public Release Notes

I. INTRODUCTION

CalDB 4.8.3.1 is an upgrade to the Chandra CalDB, which includes the following items:

• Emergency ACIS and HRC GTI_LIM File Updates

II. SUMMARY OF CHANGES

A. Emergency ACIS and HRC GTI_LIM File Updates

Location:	$CALDB/data/chandra/acis/gti_lim/
Filenames:	acisD1999-07-22gtilimN0007.fits acisD2002-11-15gtilimN0004.fits
Location:	$CALDB/data/chandra/hrc/gti_lim/
Filenames:	hrciD1999-07-22gtilimN0007.fits hrciD1999-10-04gtilimN0007.fits hrciD2002-11-15gtilimN0004.fits hrcsD1999-07-22gtilimN0007.fits hrcsD2002-11-15gtilimN0004.fits hrcsD2012-03-29gtilimN0002.fits

On Tuesday July 2, DSOps reported a significant or total loss of good time for 4 ObsIds (21582 through 21585) because of a violation of the HRMA_AFTTEMP GTI limit. The temperature exceeded the upper limit of 299.0 K during these observations. The data quality was not impacted and should have been reported as good time.

The existing limits on HRMA temperatures, HRMA gradients, and periscope gradients were originally provided by MTA before launch, and have not been updated since. In light of 15 years experience operating Chandra, the MTA lead has recommended that these GTI limits filters be removed.

See the GTI Definition page for more information on Good Time Interval determinations in processing. For technical details concerning the specific changes to the GTI_LIM files, See the Technical Details section below.

PIPELINES/TOOLS AFFECTED:

ACIS/HRC Level 1 pipeline tool mtl_build_gti: Note that mtl_build_gti works differently in the pipeline than it does in CIAO, because in the pipeline it is run twice after the L1 tool mtl_build_table is run to build the seed version of the MTL1 file. The first time through, mtl_build_gti queries the CalDB to bring in the first set of GTI limits from the CalDB, based on the instrument (INSTRUME), detector (DETNAM), observation date (DATE-OBS and DATE-END), and observation mode (OBS_MODE) values for the observation in question. The above GTI_LIM files are examples of CalDB GTI_LIM files that would be selected for non-SECONDARY OBS_MODE observations, i.e. science observations. The GTI_LIM filename is stored as keyword LIMFILE1 in the header of the "GTI_S" block of the MTL1 file in secondary data products for a given observation, and the limits listed in the GTI_LIM file are seeded into the LIMITS extension (Block 4) of the MTL1 file. The subsequent run of mtl_build_gti produces the FLT1 secondary products file, whence the GTI limits extension(s) in science observations events files are derived.

THREADS AFFECTED:

NONE.

III. TECHNICAL DETAILS

A. Emergency ACIS and HRC GTI_LIM File Updates

From the MTA Leader:

"HRMA temperature and temperature gradient were originally included in the GTI calculation due to the concern that small deviations in temperature, either trends across the periscope, optic or movement from the set point, could cause a noticeable shift in the focus. For the first ~17 years of the mission the HRMA temperatures and gradients were very stable with the exception of heater zone 50. Heater zone 50 has been stuck on for 15+ years with no noticeable impact on HRMA performance. Due to the overall heating of the spacecraft, over the last 2-3 years, parts of the HRMA have risen above their maintained temperatures and so are no longer under the strict temperature control of the first part of the mission. The net result has been a change in the nature of several monitored gradients and an increase in the overall cavity temperature. The calibration team has been actively monitoring the focus and have noticed no secular trends with the focus to date. We now understand that the thermal mass of the HRMA is such that short term (of the order of the length of an observation) changes in the temperature are small, so no individual observation will be affected by a temperature excursion. Thus, there is no continued need for HRMA temperature to drive GTI. HRMA performance is monitored as part of the quarterly review and this is the appropriate time scale upon which to evaluate changes in the HRMA."

The new GTI limits calibration files remove the following filters for all observations (all of the quantities come from the Level 1 Telescope data product telf{met}N{ver}_hkp1.fits):

• ((-1.4≤HRMA_CAPGRAD0:1)&&(HRMA_CAPGRAD0:1<1.4))
• ((-1.4≤HRMA_CAPGRAD1:1)&&(HRMA_CAPGRAD1:1<1.4))
• ((289.5≤HRMA_CAPTEMP:1)&&(HRMA_CAPTEMP:1<299.0))
• ((289.5≤HRMA_FRWDTEMP:1)&&(HRMA_FRWDTEMP:1<299.0))
• ((289.5≤HRMA_AFTTEMP:1)&&(HRMA_AFTTEMP:1<299.0))
• ((289.5≤HRMA_TEMP:1)&&(HRMA_TEMP:1<299))
• ((-1.4≤OBA_PERIGRAD0:1)&&(OBA_PERIGRAD0:1<1.4))
• ((-1.4≤OBA_PERIGRAD1:1)&&(OBA_PERIGRAD1:1<1.4))

The referenced quantities will continue to appear in the Level 1 Mission Time Line data products, but will not be used to determine the GTI filters.