CalDB 4.4.3 Public Release Notes
Public Release Date: 26 APR 2011
SDP Installation Date: 2011-04-26T20:00:00 (UTC)
CalDB 4.4.3 is an upgrade to the Chandra CalDB, which includes the following items:
- ACIS T_GAIN Epoch 44 (Nov 2010 - Jan 2011) updates
- ACIS T_GAIN Epoch 42 (May - July 2010) file corrections
- ACIS T-CTI FP_TEMP boundary condition upper limit corrections
- LETG Higher Order (m=2-10) Grating Efficiency refinements
- PIMMS Effective Area file additions -- BOOK-KEEPING ONLY
For the CIAO 4.3.1 / CalDB 4.4.3 release notes see How CalDB 4.4.3 Affects Your Analysis
II. SUMMARY OF CHANGES
The ACIS T_GAIN epoch 44 updates (which affect ACIS observations taken since August 1, 2010, and current processing) are being released in CalDB 4.4.3. The degree of epochal change in the time-dependent gain corrections is at the usual level, with relative corrections at 2% or less. For specific details of the data in this release, see the technical details section below.
See the ACIS Time-dependent Gain why page for more information.
DS and CIAO level 1 (re)processing tool acis_process_events.
The CalDB Manager has discovered and error in two ACIS T_GAIN correction files applicable to the May 1 - July 31 2010 epochal period. The problem is that the time-interpolation limits in the header of these files was not properly updated from the previous epoch, producing a systemmatic error in the PHA corrections. The errant T_GAIN files were released with CalDB 4.4.1 in December 2010. The error is less than 1/2% of the PHA or ENERGY values except when the ADU "bit" noise becomes significant in the PHA, that is, when an error of 1 ADU is greater than 0.5% of the PHA value.
While the archive has not been affected by these errant files, users who have used CIAO 4.3 and CalDB 4.4.x to reprocess OBS_IDs taken during May 1 - July 31, 2010, have incorporated this error in their new events files. Those performing imaging spectroscopy analysis particularly in energies below 1 keV are advised to reprocess their data with CalDB 4.4.3 before proceeding. For grating/ACIS-S observations from this epoch, we point out that grating energies are unaffected by T_GAIN; we have found the error does not affect order-sorting significantly.
See the CalDB Caveats page concerning this error for more details on the magnitude of the error versus PHA, at this link.
acis_process_events, for OBS_IDs with Start Dates occurring between 1 May 2010 and 31 July 2010.
Users are encouraged to reprocess their affected OBS_IDs using the thread Reprocessing Data to Generate L2 Events files
The only change to the above files here is to the CalDB boundary condition keyword "CBD10001" in Block 2 of each file. This keyword sets the allowable range of ACIS focal plane temperatures for which the files are applicable. The range has been changed from 151.16-162.16K to 151.16-159.16K. The latter is the proper calibration limit for the temperature dependent CTI correction calibrations. We know of NO OBS_IDs that would have been affected by this change.
CIAO and DS Level 1 (re)processing tool acis_process_events
No data are known to be affected by this change. Hence no threads are indicated here.
LETG higher order efficiencies have been updated to correct for over-estimates discovered by the MSFC science and LETG calibration teams. The affected orders are m=+/- 2 through 10. See the technical details section below.
The PIMMS CY13 FITS effective area files which were converted to the required ASCII files in the PIMMS Effective Areas Web page release for CY13 proposal planning, were accidentally omitted from the corresponding CalDB 4.4.1 release. This inclusion in CalDB 4.4.3 is to correct that issue. This update has NO AFFECT on users at all, since the appropriate ASCII files used by PIMMS are not the same as the FITS files stored in CalDB. These files are only needed in CalDB for future PIMMS releases in future proposal cycles.
III. TECHNICAL DETAILS
The ACIS time-dependent gain corrections (T_GAIN) have recently been updated for current changes from the previous T_GAIN epoch, specifically Epoch 44, which was Nov. 2010 through Jan. 2011. With the addition of these new corrections, derived from ACIS External Cal Source (ECS) data taken during radiation zone passes, the CalDB files extending from Aug through Oct 2010 (i.e. Epoch 43) have been finalized, and new non-interpolating T_GAIN files are now implemented for Epoch 44.
The magnitudes (in eV) of the new gain corrections, versus photon energy, are given in Figs. 1-3 below. The corrections are of the usual order in magnitude, specifically less than 2.0% of the photon energy value. Fig. 1 below gives the corrections for the ACIS-I aimpoint on chip ACIS-3, for the CTI-corrected case, which is the only one applicable to FI chips. Figure 2 gives the corrections for the ACIS-S aimpoint on ACIS-7, for the case where the BI chips are CTI-corrected. Finally Fig. 3 gives the corrections for ACIS-7 for NON-CTI-corrected BI chips. These would be relevant to GRADED DATAMODE observations with ACIS-S, for example.
The technical details concerning the correction to the ACIS EPOCH 42 T_GAIN files have been published on a separate CalDB "caveats" page, at this link.
The new N0007 LETG GREFF contains the refinements to higher order (m=+/-2 through 10) that were promised in February 2010, when the preliminary corrections to orders 2-7 were released with version N0006. The full refinements have now been completed. A thorough presentation of these changes and their derivation is available on the LETG Calibrations Web page at this link.
A comparison of the Grating Efficiencies between version N0006 and N0007 is given in Figure 4 below.
Fig. 4: Comparison of grating efficiencies from version N0006 and N0007. For clarity, even orders are on the left and odd orders on the right. The rise in the N0006 2nd order at long wavelengths, which dates to version N0004, was judged to be unphysical beyond 30 A, 2nd order is set to a constant multiple of 4th order.