Chandra Calibration Status
There have been 3 CALDB releases since the last CUC meeting
CALDB 4.1.0 Dec. 15, 2008
CALDB 4.1.1 Jan. 21, 2009
CALDB 4.1.2 Mar. 27, 2009.
HRMA
 HRMA encircled energy fraction released in CALDB 4.1.0 for use with mkpsfmap.
 Updated HRMA effective area released in CALDB 4.1.1
ACIS

Gain correction files for epochs 35 (Aug. – Oct. 2008) and 36 (Nov. 2008 Jan.2009) were released in CALDB versions 4.1.0 and 4.1.2.
HETG

Updated HETG transmission efficiencies were released in CALDB 4.1.1
Updated HRMA Effective Area
Two corrections were applied to the predictions of the raytrace code
before CALDB 4.1.1
Empirical XRCF correction
HRMA overlayer of 22A
Re-Analysis of the Ground-Based (XRCF) Data
HETG Continuum Measurement
SSD Continuum Measurement
Empirical Correction to Updated HRMA Effective Area
XMM-Newton / Chandra Cross-Calibration
Current HRMA Calibration
 Do the mirror shutters block a greater fraction of the beam than presently predicted
by the raytrace code – Analysis of HSI ring focus images show that the shutters
reduce the throughput of the mirrors by at most 1%.
 Is a greater fraction of the beam scattered beyond the 2mm pinholes used for
effective area than presently predicted by the raytrace code – The measured
2mm/35mm flux ratio is consistent with the predictions of the raytrace code below 2
keV and is approximately 3% less than the value predicted by the raytrace code at 6
keV.
 Improve the pile-up correction for the SSD continuum measurements.
 Investigate the discrepancy between FPC and SSD measurements.
HIS Ring Focus Images
Measured FPC 2mm/35mm flux ratio vs. energy
 Improve the pile-up correction for the SSD continuum measurements.
 Investigate the discrepancy between FPC and SSD measurements.
ACIS Calibration Status
Update on the ACIS Contamination Model
Spectrum of ECS L-Complex
F-K edge
ECS data fit with the old and new spectral model for the L-complex
Spectral Model
OldOld
Spectral
Model
New Spectral Model
Decline in ECS Flux with Time
Optical depth of the contaminant at 700 eV on ACIS-S
Optical depth of the contaminant at 700 eV on ACIS-I
Revised HETG Efficiencies
CALDB 4.1.1
HRC-I/ACIS Cross-Calibration with Updated HRMA Model
HRC-S QE Re-Calibration
 HRC-S 0.5-10keV QE
calibrated and fine-tuned inflight using LETG blazar
continua
 HRMA EA revision requires
QE re-calibration
 Account for:
– HRMA EA changes
– Accumulated in-flight data
suggesting overly-hard powerlaw indices than HETG+ACIS
by of order 5%
– Will require relative QE
correction between ~0.5-5keV
of ~15%
Power law Fits to contemporaneous
HETG and LETG observations of
PK2155-304
HEG
MEG
LEG
Complicated by:
• Spectral shape/intensity variability
• Parameter non-orthogonality
• Possible PL curvature
CUC Calibration Wish List
1) Astrometric Calibration
Do observers have ready access to any study of the astrometric
calibration of the mission PSF tools, e.g. if a field of sources
with well-known positions is both observed and simulated by the
PSF tools, how well do the observed and simulated data sets line up?
Astrometry - The overall 90% uncertainty in absolute positions is 0.6”. This is given on
the CXC web pages and in the POG. The mean off-set between CSC and SDSS
positions is 0.2”
On-axis PSF - There are several on-line Chandra calibration workshop presentations
as well as a discussion in the POG on this topic.
The CSC Catalog Statistical Characterization memo shows that the uncertainties in
relative astrometry for bright point sources is 0.2” within off-axis angles of 10’ and
approximately 1” at larger off-axis angles.
A study has begun to simulate a Chandra observation of the open star cluster
NGC2516 with SAOTrace and then compare the x-ray source positions as determined
by wavdetect with the optical positions.
2) ACIS Bad Pixel Table
Data discarded via entries in the ACIS Bad Pixel Table (obviously)
reduces the effective area of the mission. Currently, the standard
Bad Pixel Table aggressively removes ACIS columns and is not necessarily
appropriate for all kinds of ACIS science. Modifications to the ACIS
Bad Pixel Table should pass through an approval process which includes
consultation with the Users Committee. Several different ACIS Bad Pixel
Tables, each optimized
Data systems is revising the CIAO tool acis_build_pixel so the user
has much more freedom in specifying the bad pixels.
3) RMFs and ARFs
Users need the capability of creating RMFs and ARFs for user-selected
grades. There are several benefits:
- for bright piled-up sources filtering on only single events will
in general reduce pileup
- for faint non-piled-up sources a non-standard grade selection
can increase effective area
- for bright non-piled-up sources a non-standard grade selection
may improve energy resolution.
Since the Chandra beam is comparable to the size of an ACIS pixel, grade 0 events
are not necessarily un piled-up.
The standard grade set is 02346. In general, grades 1 and 5 add about 1-2% to the
standard grade set. For soft sources, grade 7 is heavily dominated by charged
particles. For photon energies greater than 6 keV, grade 7 events can add an
additional 10% to the standard grade set, however the background rate is 75 times
higher when including grade 7 events.
ACIS Flight Grades
Grade 0 – single
pixel
Grade 1 –
Diagonal split
Grade 2 –
vertical split
Grades 3 and 4 horizontal splits
Grade 5 – Lshaped + corner
Grade 6 – L
shaped
Grade 7 –
everything else
Grade 0 fraction vs. count rate
E0102-72
.
ACIS-I3
Grade 02346
5
ACIS-S3
1
Grade 02346
7
5
1
7
ECS Data
.
G21.5-09
ACIS-S3
E0102-72
.
ACIS-S3
ACIS-I3
Cas A
.
ACIS-S3
ACIS-I3
4) ACIS Contamination Model
5) Soft Proton Contamination
Proper statistical treatment of backgrounds requires a model of the
background spectrum, but what is this for the soft proton contamination?
In addition, what is the spatial distribution of the soft proton
contamination? Is it uniform, or is it vignetted at all by the HRMA?
The most common type of BI flare is very well-behaved, has a reproducible spectrum (a
power law with an exponential cutoff (see Markevitch et al. 2003, ApJ 583, 70), and a spatial
distribution that is non-uniform but energy-independent.
These results were presented at the 2003 Chandra Calibration meeting
(http://cxc.harvard.edu/ccr/proceedings/03_proc/presentations/markevitch2/s005.html)
This information can be added to the CIAO thread for generating background images for
extended sources. We can also provide a tool which will add in the background flare
component in a blank sky image.