CalDB 4.5.8 Public Release Notes

I. INTRODUCTION

CalDB 4.5.8 is an upgrade to the Chandra CalDB, which includes the following items:

• ACIS T_GAIN Epoch 54

For the CIAO 4.5 / CalDB 4.5.8 release notes see How CalDB 4.5.8 Affects Your Analysis.

II. SUMMARY OF CHANGES

A. ACIS T_GAIN Epoch 54

Location:	$CALDB/data/chandra/acis/t_gain/
Filename:	acisD2013-02-01t_gainN0005.fits acisD2013-02-01t_gainN0006.fits acisD2013-05-01t_gainN0002.fits acisD2013-05-01t_gain_biN0002.fits

The periodic ACIS T_GAIN correction upgrade for May - July 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 54 and 53, and so would update PHAs for OBS_IDs taken since 01 Feb 2013. 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

III. TECHNICAL DETAILS

A. ACIS T_GAIN Epoch 54

The ACIS time-dependent gain corrections (T_GAIN) have recently been updated for current changes from the previous T_GAIN epoch, specifically Epoch 54, which was May through July 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 Jan 01 2012 through April 30, 2013 (i.e. Epoch 53) have been finalized, and new non-interpolating T_GAIN files are now implemented for Epoch 54.

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 54, 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 54 inclusive, and for the positions on the respective chips given in the figure labels. (Click on images to expand the plots.)