CalDB 4.7.1 Public Release Notes

I. INTRODUCTION

CalDB 4.7.1 is an upgrade to the Chandra CalDB, which includes the following items:

• ACIS T_GAIN Epoch 64
• 2014 T_GAIN provisional and upstaged files removed from distribution

For the CIAO 4.8 / CalDB 4.7.1 release notes see How CalDB 4.7.1 Affects Your Analysis.

II. SUMMARY OF CHANGES

A. ACIS T_GAIN Epoch 64

Location:	$CALDB/data/chandra/acis/t_gain/
Filenames:	acisD2015-08-01t_gainN0005.fits acisD2015-08-01t_gainN0006.fits acisD2015-11-01t_gainN0002.fits acisD2015-11-01t_gain_biN0002.fits

The periodic ACIS T_GAIN correction upgrade for Nov 2015-Jan 2016 (Epoch 64) has been released. Modifications have also been made to the previously released Epoch 63 T_GAIN corrections (Aug-Oct '15). 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 (63 and 64), and so would update PHAs for OBS_IDs taken since 01 Aug 2015. 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. 2014 T_GAIN provisional and upstaged files removed from distribution

The following T_GAIN files have been removed from the CalDB 4.7.1 distrigution and are no longer listed in the ACIS branch index file. The first group of eight files below are 2014 provisional files that have been in CalDB for more than one year, and should no longer be used because their corresponding finalized interpolating files have been installed.

The second group of eight files are those that have been upstaged during the past year in CalDB 4.6.8 (01 July 2015) by "Revision A" files covering the same corresponding epochs. These newer files have the tag "_revA" included in their filenames. The files below were upstaged because they contain an error in their T_GAIN correction values that appeared as the External Calibration Source counting statistics became sufficiently degraded.

Location:	$CALDB/data/chandra/acis/t_gain/
Filenames of provisional 2014 T_GAINs to be deleted:	acisD2014-02-01t_gainN0002.fits acisD2014-02-01t_gain_biN0002.fits acisD2014-05-01t_gainN0002.fits acisD2014-05-01t_gain_biN0002.fits acisD2014-08-01t_gainN0002.fits acisD2014-08-01t_gain_biN0002.fits acisD2014-11-01t_gainN0002.fits acisD2014-11-01t_gain_biN0002.fits
Filenames of upstaged 2013-2014 T_GAINs to be deleted:	acisD2013-11-01t_gainN0005.fits acisD2013-11-01t_gainN0006.fits acisD2014-02-01t_gainN0005.fits acisD2014-02-01t_gainN0006.fits acisD2014-05-01t_gainN0005.fits acisD2014-05-01t_gainN0006.fits acisD2014-08-01t_gainN0005.fits acisD2014-08-01t_gainN0006.fits

III. TECHNICAL DETAILS

A. ACIS T_GAIN Epoch 64

The ACIS time-dependent gain corrections (T_GAIN) have recently been updated for current changes from the previous T_GAIN epoch, specifically Epoch 64, which was Nov 2015 - Jan 2016. 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 2015 (i.e. Epoch 63) have been finalized, and new non-interpolating T_GAIN files are now implemented for Epoch 64.

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 64, 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. The full CTI correction has been applied to the data in both figures.

Figs 4a and 4b: Long term gain trends for specific ECS line energies from Epoch 1 to Epoch 64 inclusive, and for the positions on the respective chips given in the figure labels. (Click on images to expand the plots.)