CalDB 4.5.7 Public Release Notes

I. INTRODUCTION

CalDB 4.5.7 is an upgrade to the Chandra CalDB, which includes the following items:

• ACIS T_GAIN Epoch 53
• ACIS Blank-sky BKGRND Group F BI Chips (no CTI)
• ACIS Blank-sky BKGRND_CTI Group F version 2
• HRC-S T_GMAP with GRATING=NONE

For the CIAO 4.5 / CalDB 4.5.7 release notes see How CalDB 4.5.7 Affects Your Analysis.

II. SUMMARY OF CHANGES

A. ACIS T_GAIN Epoch 53

The periodic ACIS T_GAIN correction upgrade for Feb - Apr 2013 has been released. The corrections are at nominal/expected levels of less than 2% of the energy value. This upgrade as usual affects observation data taken over Epoch 53 and 52, and so would update PHAs for OBS_IDs taken since 01 Nov 2012. Users with such datasets are encouraged to revalidate their analysis results after reprocessing their data with the upgraded CalDB files. For specific details of the new calibrations in this release, see the technical details section below.

See the ACIS T_GAIN why page for more information.

PIPELINES/TOOLS AFFECTED:

DS and CIAO level 1 (re)processing tool acis_process_events
Also: CIAO reprocessing script chandra_repro

THREADS AFFECTED:

Reprocessing Data to Create a New L2 Events File

B. ACIS Blank-sky BKGRND Group F BI Chips (no CTI)

The ACIS Group F BKGRND (effective 2009-09-21T00:00:00) have now been completed with the release of the ACIS-5 and ACIS-7 BKGRND event lists above, wherein the CTI correction has NOT been applied. These are applicable to datasets taken in GRADED mode, wherein no CTI correction is available for the back-illuminated (BI) chips.

PIPELINES/TOOLS AFFECTED:

CIAO tool acis_bkgrnd_lookup
CIAO tool reproject_events

THREADS AFFECTED:

Analysing the ACIS Background with the "Blank-Sky" Files

C. ACIS Blank-sky BKGRND_CTI Group F version 2

The ACIS GROUP F BKGRND files with CTI correction applied have been upgraded to include populated DETX,Y and SKY X,Y coordinates, which makes the files easier to view as images in the "ds9" FITS image viewer. These coordinates are artificial, and just show the non-dithered distribution of events in SKY coordinates, and are being provided for the convenience of the users. Meaningful coordinates are actually supplied to these datasets when using "reproject_events" in the thread page for "ACIS Blank-sky Background Files." See Item B above for the link.

NOTE: The "ACIS-stowed" BKGRND files in Group F have not been upgraded with these artificial coordinates due to a remaining issue with reprocessing those files to populate them. For these files, users may view the events in "ds9" by plotting in CHIPX, CHIPY coordinates.

D. HRC-S T_GMAP with GRATING=NONE

The HRC-S calibrations team has discovered that the T_GMAP files in CalDB since version 4.2.0 (2009-12-15) are not being applied to HRC-S observations with no grating present (GRATING=NONE in the event headers). Instead, the old GMAP file without the time-dependence is being applied by default, both in the CIAO "chandra_repro" script, and in standard data processing with "hrc_process_events" (in the HRC Level 1 pipeline).

The cause for this problem is that the T_GMAP CalDB files from the beginning have been indexed with GRATING = LETG in the file headers and thus in the HRC branch index. The immediate fix for this is to set GRATING = NONE in the index and the T_GMAP CalDB file headers. This causes the T_GMAP to be applied to all cases of GRATING, because "NONE" is the null value key configuration file for HRC; that is to say, GRATING values are ignored in this case, and all HRC-S data get the T_GMAP.

Users should read the technical details section below to determine whether their non-grating HRC-S OBS_ID(s) have been affected by this header error in T_GMAP. Affected users may simply run CIAO script "chandra_repro" to correct the problem, once they have upgraded to CalDB 4.5.7 or later version.

See the HRC-S Time-dependent Gain Corrections and PI Filter why page for more information.

PIPELINES/TOOLS AFFECTED:

HRC Level 1 (re)processing tool hrc_process_events
Also, CIAO 4.5 reprocessing script chandra_repro

THREADS AFFECTED:

Reprocessing Data to Create a New Level=2 Event File

III. TECHNICAL DETAILS

A. ACIS T_GAIN Epoch 53

The ACIS time-dependent gain corrections (T_GAIN) have recently been updated for current changes from the previous T_GAIN epoch, specifically Epoch 53, which was February through April 2013. 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 November 01 2012 through Jan 2013 (i.e. Epoch 52) have been finalized, and new non-interpolating T_GAIN files are now implemented for Epoch 53.

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.

Fig. 1: ACIS-I3 aimpoint T_GAIN corrections in eV versus photon energy.

Fig. 2: ACIS-S3 CTI-corrected aimpoint T_GAIN corrections in eV versus photon energy.

Fig. 3: ACIS-S3 non-CTI-corrected aimpoint T_GAIN corrections in eV versus photon energy.

Long term trends for chips I3 and S3 are plotted below in Figure 4a and b, through Epoch 53, the latest release. The chip locations for these plots are given in the respective labels above the plots. Note that the location is not the aimpoint position, as with Figs. 1-3 above.

Figs 4a and 4b: Long term gain trends for specific ECS line energies from Epoch 1 to Epoch 53 inclusive, and for the positions on the respective chips given in the figure labels. (Click on images to expand the plots.)

B. ACIS Blank-sky BKGRND Group F BI Chips (no CTI)

With the release of these two new blank-sky background files for the back-illuminated chips, and with no CTI correction applied, the Group F BKGRND datasets are now complete. The respective files for ACIS-S1 (ACIS-5) and ACIS-S3 (ACIS-7) were compiled from the same sets of blank-field observations as their CTI-corrected counterparts, which were released with CalDB 4.5.6 in February 2013. With the CTI correction removed, certain additional bad pixels have appeared in the datasets, and have been removed from the new event lists as a matter of course.

The modified text file README_ACIS_BKGRND_GROUPF.txt gives the details regarding the compilation of these two non-CTI events lists that are included with the current Group F BKGRND upgrade.

As with the corresponding CTI-corrected events lists, the spectra have not changed a great deal from Group E to F, though that is still under some study by the Calibration Team. See Figures 5 and 6 below.

Fig. 5: The full spectra (no VF cleaning) for ACIS-S1 (ACIS-5) background events, for Group E (black) versus Group F (red).

Fig. 6: The full spectra for ACIS-S3 (ACIS-7) background events, for Group E versus Group F.

D. HRC-S T_GMAP with GRATING=NONE

The name of the GMAP or T_GMAP file applied to HRC-S event lists (regardless of the presence of a grating) is stored in the "GAINCORF" header keyword. Therefore, users of affected HRC-S non-grating OBS_IDs may identify whether or not the correct T_GMAP file or the older GMAP file has been applied in their datasets by displaying the keyword as follows.

unix% dmkeypar *evt2.fits GAINCORF echo+

If the resulting value of the keyword is either of these two filenames:

hrcsD1999-07-22t_gmapN0002.fits
hrcsD2012-03-29t_gmapN0002.fits

then the time-dependent GMAP has been applied to the OBS_ID already, and the user need do nothing.

If the value of the keyword is "hrcsD1999-07-22gmapN0001.fits", then the old GMAP has been applied. With the installation of CalDB 4.5.7 (or later version), the user may update to the time-dependent GMAP by running the CIAO "chandra_repro" script on their particular OBS_ID.

Furthermore, with the installation of CalDB 4.5.7 in Standard Data Processing, all archived HRC-S non-grating OBS_IDs will be reprocessed and updated. At the time of publication of this web page, all 69 of these OBS_IDs have been identified and queued for reprocessing, which will proceed as of the "SDP Date" given at the top of this page.