CALDB RELEASE NOTES
Version: 2.6
CALDB Effective Date: 2001-06-01T19:59:00 (3:58pm EDT)

I. Summary of Changes

A. HRC-S DEGAP Version 2

Filename: hrcsD1999-07-22gapN0002.fits
in $CALDB/data/chandra/hrc/bcf/degap/

B. -100C ACIS OSIP table, Version 5

Filename: acisD1999-08-13osipN0005.fits
in $CALDB/data/chandra/acis/cpf/osip/

C. ACIS QE version 4, for use with LETG/ACIS-S only

Filename: acisD1997-04-17qeN0004.fits
in $CALDB/data/chandra/acis/bcf/qe/

File must be selected by hand for use in CIAO.

D. GTI_LIM file changes

Filenames: acisD1999-07-22gtilimN0003.fits
in $CALDB/data/chandra/acis/bcf/gtilim/
	   hrciD1999-07-22gtilimN0003.fits
	   hrciD1999-10-04gtilimN0003.fits
	   hrcsD1999-07-22gtilimN0003.fits

The only change here is that the altitude lower limit of
60,000 km, originally included to exclude radiation zone
from giving good time intervals in any case, has been
removed from the N0003 files.


II. Technical Reports

A. HRC-S Degap upgrade v2:

This new degap correction file removes difficulties for imaging with
HRC-S, caused by an inadequate degap specification in the N0001 file
for low U and high U column numbers. This resulted in a non-correction
for the degap in a number of CAL observations, and any observations with
point sources near the long edges of the S2 plate.

This new degap map is NOT a final solution, as the PSF performance is not
yet what is expected for sources within a few arc minutes of the axis. Hence,
while there is a significant improvement for edge point sources, it should
clearly be possible to improve on the point source resolution with a better
correction map, to be expected around August 1, 2001 (version 3).

Thread affected: The new HRC-S degap correction thread.
http://asc.harvard.edu/ciao/threads/hrcsdegap.thread.html

B. -100C OSIP version 5:

For OAC grating observations, the N0004 OSIP (order sorting and integrated
probability) table is clipping events severely and asymmetrically between
+ and - orders. This is due to the onset of ACIS CTI problems in the FI chips
between August 12, 1999 and August 28, 1999, when the first HETG/ACIS-S 
grating data of Capella were being taken.

Public OBSIDs 1099, 1100, 1101, 1235, 1236, and 1237 were badly affected,
losing 60% of counts in the negative 1st order over 12-16A of the MEG, and
up to 85% of events at 14A in the HEG-1 order. 

By opening the negative acceptance angle in (grating order) x 
(order-wavelength)
space in the first order, one is able to recover most of the symmetry, although
the correction is still not perfect. What is literally needed is a better
gain-response calibration during that ramping period of damage to ACIS
near late August 1999. However this is not likely to come in the near future,
so this file will have to do for now.

Threads affected: 

mkgarf (mkgarf_acis) (CIAO)
http://asc.harvard.edu/ciao/threads/mkgarf.hetgacis.html#osip
http://asc.harvard.edu/ciao/threads/mkgarf.letgacis.html#osip

Grating L1.5 with ACIS, aka tg_resolve_events (CIAO and SDP)
http://asc.harvard.edu/ciao/threads/spectra.hetgacis.html#hetg.thread.B.Generate1.5.html
http://asc.harvard.edu/ciao/threads/spectra.letgacis.html#letg.thread.B.Generate1.5.html

C. ACIS QE version 4, user-selectable file:

Details are posted at http://space.mit.edu/CXC/calib/letg_acis/ck_cal.html.
For some time now we have known that residuals have remained in fits
of continuum sources in LETG/ACIS observations near the carbon edge (3C273
for example). An attempt is being made to correct the residual  with an
as yet unaccounted-for enhancement of the Carbon-K edge absorption features,
which has been consigned to the Optical Blocking Filter transmission. 
The CAL team considers this change likely applies to the whole of ACIS-S
only (so far), but can only confirm an improvement in fitting of observation
data for the LETG/ACIS-S configuration, with a 10mm sim-z offset, moving
the LETG pattern nearer the ACIS-S chip readouts. (This reduces the CTI 
losses).

This new file needs to be selected manually by the user, as indicated
in the threads below:

LETG/ACIS-S Grating ARFs:
http://asc.harvard.edu/ciao/threads/mkgarf.letgacis.html#osip

HETG/ACIS-S Grating ARFs:
http://asc.harvard.edu/ciao/threads/mkgarf.hetgacis.html#osip
(Optional use here)

ACIS-S imaging (ACIS-S3, optional): 
Exposure Maps
http://asc.harvard.edu/ciao/threads/expmap.single.html#createinstmap
http://asc.harvard.edu/ciao/threads/expmap.multi.html#createinstmap

ARFs with mkarf (ACIS-S3, optional)
http://asc.harvard.edu/ciao/threads/psextract.thread.html#script
http://asc.harvard.edu/ciao/threads/pieces.thread.html#ARF