Calibration Status

Chandra has been in orbit for over 18 months and the calibration database (CALDB) is now fully populated with over 60 calibration products. The CALDB contains calibration products for all of the focal plane instruments, gratings, mirrors, and aspect system. The calibration team recently compiled a calibration status report which is linked to the Chandra Instruments and Calibration Web page (cxc.harvard.edu/cal/ Cal_Status_Report/). This report shows that approximately 80% of the calibration products are accurate to better than than a 3% level. The report gives a brief summary of each calibration product, whether there are any known problems, a one or two sentence description of the problem, and an estimate on when a revised product will be available. In addition to the calibration status report, further information about the remaining calibration uncertainties can be found on the Chandra Instruments and Calibration web page under the links to the individual detectors and gratings. These results can be summarized as follows.

ACIS

An analysis of LETG/ACIS-S observations of PKS 2155-304 shows that there is a $\sim$20eV offset between the mean pulse heights and true energies for energies between about 400 and 1000 eV, and larger differences due to the event threshold at lower energies. There is also evidence that the S3/S2 QE ratio is larger than expected by 10% below 1.5 keV. See the memo posted at:

http://cxc.harvard.edu/cal/Acis/Cal_projects/index.html

for more details about present ACIS calibration uncertainties.

HRC-I

The HRC-I QE below 200eV may be overestimated by a factor of approximately 2. Above 1keV, the QE is good to about 7%.

HETG

The present calibration products have a 10% systematic difference between HEG and MEG efficiencies. See the memo posted at:

http://space.mit.edu/ASC/calib/hetgcal.html

for more details about the present calibration status of the HETG.

LETG

The LETG/HRC-S effective area is uncertain by as much as 15% at some energies. See the memo posted at:

http://cxc.harvard.edu/cal/Letg/calstatus.html

for more information.

HRMA

A long exposure of 3C273 with ACIS-S has been used to study the wings of the PSF. This observation shows that there is more power scattered beyond 20 arcseconds than predicted by the most recent version of the ray trace program. This can have important consequences regarding the studies of dust halos around bright point sources. See the memo posted at:

http://cxc.harvard.edu/cal/Hrma/psf/PSF_wings_3c273/psf_wings.html

for more details.

- Larry David