CalDB 4.4.4 Public Release Notes

I. INTRODUCTION

CalDB 4.4.4 is an upgrade to the Chandra CalDB, which includes the following items:

• ACIS T_GAIN Epoch 45
• ACIS -120C non-CTI GAIN FILE
• ACIS T_GAIN Epoch 43 N0006
• PCAD ALIGN files version N0008 with Periscope Align Correction Extension

For the CIAO 4.3 / CalDB 4.4.4 release notes see How CIAO 4.3 and CalDB 4.4.5 Affect Your Analysis

II. SUMMARY OF CHANGES

A. ACIS T_GAIN Epoch 45

Location:	$CALDB/data/chandra/acis/t_gain/
Filename:	acisD2010-11-01t_gainN0006.fits acisD2010-11-01t_gainN0005.fits acisD2011-02-01t_gain_biN0002.fits acisD2011-02-01t_gainN0002.fits

The periodic ACIS T_GAIN correction upgrade for Feb-Apr 2011 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 45 and 44, and so would update PHAs for OBS_IDs taken since 01 November 2010. 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 data in this release, see the technical details section below.

See the ACIS Time-dependent 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 for ACIS data with DATE-OBS after (UTC) 2010-11-01T00:00:00.

THREADS AFFECTED:

Reprocessing Data to Create a New L2 Events File

B. ACIS -120C non-CTI GAIN FILE

Location:	$CALDB/data/chandra/acis/det_gain/
Filename:	acisD2000-01-29gainN0005.fits

This change only affects engineering OBS_IDs (OBS_MODE=SECONDARY) in the MTA pipeline, when their FP_TEMP levels are beyond the standard range of applicability (148.16K-158.16K). Users should ignore this upgrade.

PIPELINES/TOOLS AFFECTED:

MTA pipeline "mta_monitor_events" for ACIS ERs with high FP_TEMPs only.

THREADS AFFECTED:

None.

C. ACIS T_GAIN Epoch 43 N0006

Location:	$CALDB/data/chandra/acis/t_gain/
Filename:	acisD2010-08-01t_gainN0006.fits

An error was found the the header of the above file wherein the CTI_APP boundary condition was set to "(PPPPPBPBPP,NNNNNNNNNN)" which means that the file would be selected not only for fully CTI-corrected data, but also completely non-CTI corrected data, for OBS_IDs with DATE-0BS between 2010-08-01T00:00:00 and 2010-11-01T00:00:00, under the following conditions in acis_process_events:

• Parameter apply_cti is set to "no".
• Parameter apply_tgain is set to "yes".

The most frequent situation where this happens is in the MTA pipeline "mta_monitor_events" when the CTI correction is removed from the data, while still applying the T_GAIN. The correct file to apply in such a case is actually acisD2010-08-01t_gainN0005.fits. The only difference between the N0005 and the N0006 files are the t_gain corrections for the BI chips.

The users who would be affected by this error are those who, since having installed CalDB 4.4.3 (released 26 April 2011), have used acis_process_events to do the following:

• remove the CTI correction (pset apply_cti=no)
• applied the T_GAIN correction (apply_tgain=yes)
• to OBS_IDs taken since UTC 2010-08-01T00:00:00
• analyzed the resulting BI chip data.

Any such users should repeat that analysis after repeating the above sequence of steps with the CalDB 4.4.5 upgrade installed. Note that users who reapply the CTI correction and then analyze are NOT affected by this error.

PIPELINES/TOOLS AFFECTED:

The MTA pipeline "mta_monitor_events".

acis_process_events with parameter apply_cti set to "no" and apply_tgain set to "yes".

THREADS AFFECTED:

NONE, as the threads do not instruct users to remove the CTI corrections.

D. PCAD ALIGN files version N0008 with Periscope Align Correction Extension

Location:	$CALDB/data/chandra/pcad/align/
Filename:	pcadD{yyyy-mm-dd}alignN0008.fits There are 51 ALIGN files in CalDB.

The aspect periscope alignment correction was released into Standard Processing with DS 8.4 on 28 June 2011. The Aspect team describes the basic issue as follows:

"Temporal drift in X-ray source positions can occur due to changes in the periscope alignment which induce drift in fid light positions as observed by the Aspect camera. Further analysis of the periscope alignment drift reveals that approximately 300 observations may be affected with drifts of more than 0.1 arcseconds.

"A pre-launch calibration of the periscope gradients to periscope alignment does exist, but we performed a recalibration using on-orbit data that reveals that the pre-launch coefficients may be off by up to a factor of 10. This new calibration is used in this tool to correct fid light positions based on telemetered periscope gradients."

See the technical details section below for more details and links.

PIPELINES/TOOLS AFFECTED:

ASPECT Level 1 pipeline in Standard Data Processing.

THREADS AFFECTED:

None.

III. TECHNICAL DETAILS

A. ACIS T_GAIN Epoch 45

The ACIS time-dependent gain corrections (T_GAIN) have recently been updated for current changes from the previous T_GAIN epoch, specifically Epoch 45, which was Feb. through Apr. 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 Nov 2010 through Jan 2011 (i.e. Epoch 44) have been finalized, and new non-interpolating T_GAIN files are now implemented for Epoch 45.

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.

D. PCAD ALIGN files version N0008 with Periscope Align Correction Extension

The Aspect group has posted the following links for information on the periscope alignment algorithm, and the corresponding input CalDB data that has been installed in the implementation in DS 8.4. See:

• Add the Periscope Correction to the Aspect Pipeline
• Add PERIFIDCORR HDU to PCAD CALALIGN CALDB files