CalDB 4.6.7 Public Release Notes

I. INTRODUCTION

CalDB 4.6.7 is an upgrade to the Chandra CalDB, which includes the following items:

• ACIS T_GAIN Epoch 60
• HRC-S QEU 2008 Header Correction
• Retiring ACIS 2013 Provisional T_GAINs

For the CIAO 4.7 / CalDB 4.6.7 release notes see How CalDB 4.6.7 Affects Your Analysis.

II. SUMMARY OF CHANGES

A. ACIS T_GAIN Epoch 60

Location:	$CALDB/data/chandra/acis/t_gain/
Filenames:	acisD2014-08-01t_gainN0005.fits acisD2014-08-01t_gainN0006.fits acisD2014-11-01t_gain_biN0002.fits acisD2014-11-01t_gainN0002.fits

The periodic ACIS T_GAIN correction upgrade for Nov-Jan 2015 (Epoch 60) 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 the two most recent T_GAIN Epochs (59 and 60), and so would update PHAs for OBS_IDs taken since 01 Aug 2014. 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. HRC-S QEU 2008 Header Correction

Location:	$CALDB/data/chandra/hrc/qeu/
Filename:	hrcsD2008-01-01qeuN0007.fits

The CalDB Manager has discovered a previously unnoticed error in the header of Block 3 of the 2008 HRC-S QEU file version N0007, release with CalDB 4.6.5 in December of 2014. It is a typo in the CVED0001 keyword, rendered as "20-9-01-07T00:00:00" rather than "2009-01-07T00:00:00". The result is that the END_TIME value generated in the index from the CVED keyword is erroneous, and that particular block listing is never selected. Instead the corresponding block 3 of the older QEU file version N0006 is selected instead.

This is actually a non-problem for users, because both of the 2008 N0006 and N0007 QEU files for HRC-S contain the same identical data sets, and the incorrect block selection in ardlib.par has zero affect on the calibrations selected. However, the N0007 file must be corrected in case the N0006 file should be retired in the future, and removed from the CalDB distribution. LETGS users will not likely notice the correction unless they look at the headers of specific GARF files, where the HISTORY in those headers will give the names of the QEU files and blocks selected from CalDB.

PIPELINES/TOOLS AFFECTED:

None.

THREADS AFFECTED:

None.

C. Retiring ACIS 2013 Provisional T_GAINs

Location:	$CALDB/data/chandra/acis/t_gain/
Files to be deleted from CalDB:	acisD2013-02-01t_gainN0002.fits acisD2013-02-01t_gain_biN0002.fits acisD2013-05-01t_gainN0002.fits acisD2013-05-01t_gain_biN0002.fits acisD2013-08-01t_gainN0002.fits acisD2013-08-01t_gain_biN0002.fits acisD2013-11-01t_gainN0002.fits acisD2013-11-01t_gain_biN0002.fits

The above files have been marked as BAD (CAL_QUAL=5) in the ACIS index for at more than one year. At this point it is time to remove them from the distribution so that they will reduce the CalDB download file size, as well as to prevent them from being used again, as they only contain provisional data to be applied in the absence of the final versions (N0006 or N0005) of the files corresponding to the same validity dates.

PIPELINES/TOOLS AFFECTED:

None.

THREADS AFFECTED:

None.

III. TECHNICAL DETAILS

A. ACIS T_GAIN Epoch 60

The ACIS time-dependent gain corrections (T_GAIN) have recently been updated for current changes from the p revious T_GAIN epoch, specifically Epoch 60, which was Nov-Jan 2015. With the addition of these new corrections , derived from ACIS External Cal Source (ECS) data taken during radiation zone passes, the CalDB files extendin g from Aug-Oct 2014 (i.e. Epoch 59) have been finalized, and new non-interpolating T_GAIN files are now impleme nted for Epoch 60.

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 o nly 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 60, the latest release. The chip locations for these plots are given in the respective labels above the plots. Note that the locations are not the aimpoint positions, as with Figs. 1-3 above, but are near the centers of each chip.

Figs 4a and 4b: Long term gain trends for specific ECS line energies from Epoch 1 to Epoch 60 inclusive, and for the positions on the respective chips given in the figure labels. (Click on images to expand the plots.)