ACIS Calibration Information
This page contains current and historical documents regarding calibration of Chandra's Advanced CCD Imaging Spectrometer (ACIS). Items are organized by topic (see menu on left) and are ordered by date for each topic, with most recent items at the top. For topics with on-going monitoring or calibration (e.g. background, gain correction) the status is summarized at the top of the section. Please see also these additional resources:- ACIS chapter in Proposers' Observatory Guide
- CIAO data analysis guides for the ACIS
- ACIS products in the Calibration Database
- All ACIS-related Chandra Calibration Review presentations
- MIT ACIS Home Page
- PSU ACIS Home Page
- HETG Observer Information
- LETG Observer Information
- Chandra Data Archive: SPIE papers
Background
- Status Blank sky datasets and ACIS "stowed" datasets are available in the CALDB.
- Old blank sky datasets and "stowed" datasets and tools for modeling the quiescent background, created by Maxim Markevitch, can be found at Maxim's ACIS background page. [Apr 2009; deprecated]
- New Background Rates [updated 2023 Oct]:
- Total telemetered background rates (including all grades
and the upper event cutoff at 15 keV) for chips S2
(FI) and S3 (BI) as a function of time. Vertical dashed lines
are year boundaries. Data are plotted through late-August 2017.
Beginning in Cycle 11 (late 2009) the default high energy limit
was changed from 15 keV to 13 keV.
Subsequent 15 keV rate estimates were scaled from 13 keV rates using
13 kev/15 keV conversion factors of 0.82 for S2 and and 0.68 for S3.
These factors were determined from observations (April-July 2009)
when the rates were fairly constant, and with the onboard high
energy limit set to either 15 keV or to 13 keV.
[Click on the figure for a PDF version.]
- Typical total quiescent background rates (cts/s/chip; 2019, averaged April through early October),
including all grades that are telemetered (not just standard
ASCA grades), by chip type and upper energy cutoff.
These values can be used to estimate the probability of telemetry
saturation. Note that the rates have been increasing rapidly in 2016; users should
take into account the likelihood of further increases during this cycle.
Beginning in Cycle 11 (late 2009) the default high energy limit
was changed from 15 keV to 13 keV.
Subsequent 15 keV rate estimates were scaled from 13 keV rates using
13 kev/15 keV conversion factors of 0.82 for S2 and and 0.68 for S3.
These factors were determined from observations (April-July 2009)
when the rates were fairly constant, and with the onboard high
energy limit set to either 15 keV or to 13 keV.
†Scaled from 13 keV ratesPeriod (keV) Aug 1999 2000-2003 2009 2023 (January - mid October) Upper E cutoff 15 keV 15 keV 15 keV 15 keV† 13 keV 12 keV 10 keV Chip S2 (FI) 10 6.3 10.7 5.4 4.5 4.4 4.0 Chip S3 (BI) 11 7.7 14.7 8.9 6.0 5.5 4.0 - Approximate on-orbit standard grade background counting
rates (2019, averaged July to mid-September).
The rates are cts/s/chip,
using only ASCA grades 02346, no VF filtering,
excluding background flares and bad
pixels/columns and celestial sources identifiable by eye.
These values can be used for sensitivity calculations
Energy Band (keV) I0 I1 I2 I3 S1 S2 S3 S4 0.3-10.0 0.35 0.36 0.35 0.39 1.93 0.37 1.00 0.36 0.5-2.0 0.06 0.06 0.06 0.07 0.17 0.07 0.14 0.08 0.5-7.0 0.17 0.20 0.20 0.23 0.52 0.21 0.63 0.19 5.0-10.0 0.19 0.20 0.18 0.21 1.40 0.20 0.63 0.19 10.0-12.0 0.12 0.12 0.11 0.12 1.10 0.12 0.79 0.12
- Total telemetered background rates (including all grades
and the upper event cutoff at 15 keV) for chips S2
(FI) and S3 (BI) as a function of time. Vertical dashed lines
are year boundaries. Data are plotted through late-August 2017.
Beginning in Cycle 11 (late 2009) the default high energy limit
was changed from 15 keV to 13 keV.
Subsequent 15 keV rate estimates were scaled from 13 keV rates using
13 kev/15 keV conversion factors of 0.82 for S2 and and 0.68 for S3.
These factors were determined from observations (April-July 2009)
when the rates were fairly constant, and with the onboard high
energy limit set to either 15 keV or to 13 keV.
- Memos and papers:
- Chandra ACIS detector background uniformity from ACIS "stowed" backgrounds T. Gaetz, 24 Feb 2014
- Particle background observations: dark Moon and ACIS stowed (PDF) M. Markevitch, 27 Dec 2005
- Chandra Spectra of the Soft X-Ray Diffuse Background (PDF), M. Markevitch, et al., 2003, ApJ 583, 70
- Reducing ACIS quiescent background using Very Faint mode, A. Vikhlinin, 22 Oct 2002
- Using Chandra Level 0 Event Histogram Files to Characterize the High-Energy Particle Background (PDF), B. Biller, P. Plucinsky & R. Edgar, 22 Jan 2002
- The Temporal Characteristics of the Chandra X-ray Observatory High Energy Particle Background (PDF), C.E. Grant, M.W. Bautz & S.N. Virani, 2002, ASP Conference Proceedings, 262, 401
- General discussion of the quiescent and flare components of the ACIS background, M. Markevitch, 28 Sep 2001
- ACIS background measurement prior to opening the mirror cover (PDF), F. Baganoff, 1 Sep 1999
Bias
- Memos:
- (Re)processing and Analysis Issues for ACIS Data, G. Allen, CIAO Workshop Presentation, 2008
CC Mode Calibration
- Updated (Ver. 3, 2014 Feb 26) Calibration and analysis of Chandra HETG spectra observed in CC-mode, see Calibration Properties of Chandra HETG Spectra Observed in CC-Mode (PDF)
- Chandra Calibration Review presentations on CC Mode, N. Shulz, Feb 2014
Cross Calibration
- Papers:
-
- New SNR 1E0102.2-7219 as an X-ray Calibration Standard in the 0.5-1.0 keV Bandpass and Its Application to the CCD Instruments aboard Chandra, Suzaku, Swift and XMM-Newton (PDF), Paul P. Plucinsky, Andrew P. Beardmore, Adam Foster, Frank Haberl, Eric D. Miller, A.M.T. Pollock, and Steve Sembay, SPIE, 2016
- Cross-calibration of the X-ray Instruments onboard the Chandra, INTEGRAL, RXTE, Suzaku, Swift, and XMM-Newton Observatories using G21.5-0.9, Tsujimoto et al, 2010 (A&A preprint)
- Cross-calibrating X-ray detectors with clusters of galaxies: an IACHEC study, Nevalainen et al, 2010 (A&A preprint)
- The SMC SNR 1E0102.2-7219 as a Calibration Standard for X-ray Astronomy in the 0.3-2.5 keV Bandpass (PDF), Paul P. Plucinsky, Frank Haberl, Daniel Dewey, Andrew P. Beardmore, Joseph M. DePasquale, Olivier Godet, Victoria Grinberg, Eric D. Miller, A.M.T. Pollock, Steve Sembay, Randall K. Smith, SPIE, 2008
Charge Transfer Inefficiency (CTI)
- Status The GRADED mode CTI correction and temperature-dependent CTI correction are included in acis_process_events as of CIAO 4.3. [Dec 2010]
- ACIS CTI @ -120C: Monitoring and analysis of ACIS CTI by the instrument team, C. Grant, updated monthly
- Memos and papers
- Approximate correction for parallel CTI in GRADED mode data (PDF), A. Vikhlinin, CXC Memo, 19 March 2007
- Temperature dependence of charge transfer inefficiency in Chandra X-ray CCDs (PDF), C. Grant, M. Bautz, S. Kissel, B. LaMarr & G. Prigozhin, SPIE, 2006
- Long-term trends in radiation damage of Chandra x-ray CCDs (PDF), C. Grant, M. Bautz, S. Kissel, B. LaMarr & G. Prigozhin, SPIE, 2005
- A charge transfer inefficiency correction model for the Chandra Advanced CCD Imaging Spectrometer (PDF), C. Grant, M. Bautz, S. Kissel & B. LaMarr, SPIE, 2004
- Modeling Charge Transfer Inefficiency in the Chandra Advanced CCD Imaging Spectrometer (PDF), L. Townsley, P. Broos, J. Nousek & G. Garmire, NIMPA, 2002
- Mitigating Charge Transfer Inefficiency in the Chandra X-ray Observeratory Advanced CCD Imaging Spectrometer (PDF), L. Townsley, P. Broos, G. Garmire & J. Nousek, ApJ, 2000
- CTI-Induced Quantum Efficiency Loss in ACIS Front Illuminated Devices [5 Apr 2000]
Detector Geometry
- ACIS Flight Focal Plane, Fig 6.1 in POG
Energy Resolution
- Note: Also see section on charge transfer inefficiency and ACIS Gain and Spectral Resolution.
- Memos
- Resolution of ACIS Devices at -110 C, -120 C, and -123 C, B. LaMarr [10 Jan 2000] (PDF version also available)
- ACIS Flight Energy Scale and Resolution as a Function of Row (PDF), B. LaMarr [5 Nov 1999]
- ACIS Spectral Resolution Analysis, N. Schulz [5 Feb 1999]
Event Grades
- Chandra Calibration Review presentations tagged with "event grade"
- Chandra Calibration Review presentations tagged with "grade morphing"
- Memos
-
- Pre-Flight Event Grade Branching Ratios [6 Nov 1998]
- The branching ratio technique for the depletion depth measurement, G. Prigozhin, ACIS Memo [5 Aug 1997]
- Pix_dist Simulated Branching Ratio, T. Isobe, ACIS Memo [25 Oct 1996]
Gain
- The ACIS gain is calibrated by co-adding data from the external calibration source (ECS). Prior to 2017, time-dependent gain correction files were released in the CALDB every 3 months. Due to the continued fading of the ECS, which is composed of a 55Fe source with a half-life of 2.7 years, the ECS data must be co-added over 6 month to acquire sufficent photon statistics. Since the beginning of 2017, time-depdent gain correction files are released in 6 month intervals in the CALDB.
- Status We continue to produce time-dependent gain corrections (TGAIN). The gain epochs are now 6 months.
- ACIS gain @ -120 C: Monitoring and analysis for the ACIS gain by the instrument team, C. Grant, updated monthly
- Memos
- Corrections for time-dependence of ACIS gain (PDF), A. Vikhlinin, R. Edgar & N. Schulz [30 July 2004]
Hot/Bad Pixels
- ACIS Bad Pixels and Columns for FP temperature=-120 C, R. Edgar & M. Markevitch [21 Feb 2005]
- ACIS Bad Pixels and Columns for FP temperature=-100 C, B. McNamara & A. Ware [7 Jan 2000]
- Hot Pixels in FI Devices (for -90C and -60C) (PDF), M. Pivovaroff [20 Sep 1999]
Miscellaneous
FEP0 Problem
- Status There has not been a recurrence of the FEP0 anomaly in ~10 years. [Dec 2010]
- Summary [2 Feb 2000]
Ground Calibration
- Science Instrument (SI) Calibration Report for the AXAF CCD Imaging Spectrometer (ACIS) (PDF) [Jan 1999]
- Joint AXAF high-resolution mirror assembly and AXAF CCD Imaging Spectrometer calibration at the MSFC X-ray calibration facility, Nousek J, et al., 1998, Proc. SPIE, 3444, 225
- Misc. pre-flight links
Transfer Streak Calibration
- Memos and papers
- Analysis of the Chandra On-Orbit PSF Wings (PDF), T. Gaetz [3 Nov 2010]
- Summary, R. Edgar [8 Dec 2006]
- A Chandra X-ray Study of the Dense Globular Cluster Terzan 5 (PDF), C. Heinke, P. Edmonds, J. Grindlay & D. Lloyd, ApJ, 2003
Optical Blocking Filter and Contamination
- Status An updated contamination model (N0007) is included in CALDB 4.4.10. [Jun 2012]
- Memos and papers
- Update to the ACIS Contamination Model [8 Jan 2010]
- ECS line fluxes and illumination pattern from the Ball dataset (PDF), A. Vikhlinin [18 Feb 2009]
- Contamination on the ACIS OBF and Changes in the Low Energy QE [7 Dec 2004]
- Spatial structure in the ACIS OBF contamination (PDF), A. Vikhlinin [9 May 2004]
- Verifying the ACIS Contamination Model with 1E0102.2-7219 (PDF), J. DePasquale, P. Plucinsky, A. Vikhlinin, H. Marshall, N. Schulz & R. Edgar, SPIE, 2004
- Composition of the Chandra ACIS contaminant (PDF), H. Marshall, A. Tennant, C. Grant, A. Hitchcock, S. O'Dell & P. Plucinsky, SPIE, 2003
- In-Flight Optical Blocking Filter Transmission [10 March 2000]
Pileup
- Memos
- Analysis of the Chandra On-Orbit PSF Wings (PDF), T. Gaetz [3 Nov 2010]
- Pileup Modeling and Analysis Tools, J. Davis, HEAD presentation [31 May 2002]
- Pileup Summary [7 Oct 1998]
- ACIS Pileup: Analysis of XRCF Phase H Data (PDF), J. Kastner, K. Allen & K. Glotfelty [24 Feb 1998]
- An Analytic ACIS Pileup Model (PDF), B. McNamara [2 Oct 1997]
- HEXS Flat Field Pileup Analysis (PDF), S. Jones [2 Aug 1997]
Spatial Resolution, Encircled Energy and PSF
- Memos
-
- Analysis of the Chandra On-Orbit PSF Wings (PDF), T. Gaetz [3 Nov 2010]
- Analysis of Chandra PSF feature using ACIS data V. Kashyap [Oct 2010]
- XRCF Point Spread Function Analysis A. Ware & B.R. McNamara [30 Apr 1999]
Quantum Efficiency and QE Uniformity
- Note: Also see sections on OBF contamination and charge transfer inefficiency.
- Chandra Calibration Review presentations on ACIS QE
- Chandra Calibration Review presentations on ACIS QEU
- ACIS QE plots and data [19 Aug 2004]
- Memos
- Time-dependent ACIS QEU maps [Dec 2012]
- Contamination on the ACIS OBF and Changes in the Low Energy QE [7 Dec 2004]
- Absolute QE of ACIS S1, S2, and S3 from XRCF data at selected energies (PDF), R. Edgar & A. Vikhlinin [11 Aug 2004]
- High-resolution QEU maps for ACIS-I and S1,2,3 chips (PDF), A. Vikhlinin [14 Apr 2004]
- Absolute QE of ACIS S2 and S3 from XRCF data at Oxygen K-alpha and Copper L-alpha (PDF), R. Edgar [13 Nov 2003]
- CTI-Induced Quantum Efficiency Loss in ACIS Front Illuminated Devices [5 Apr 2000]
Response Matrices
- Memos
- In-flight calibration of the ACIS spectral response (PDF), A. Vikhlinin [2006 January 16]
- Updates to the RMF model in the ACIS FI CCDs (PDF), A. Vikhlinin [2004 March 22]
- Release of FEF files for CTI Corrected front-illuminated ACIS chips at -120 C (PDF), R. Edgar [4 Feb 2003]
- New S3 Response Products Release Notes, R. Edgar [9 Aug 2001]
Subpixel Event Repositioning
- Status From CIAO 4.3 release notes: "As of CIAO 4.3, the default pixel adjustment in acis_process_events is the sub-pixel event-repositioning algorithm 'EDSER' described in Li et al." (2004, ApJ, 610, 1204) [Dec 2010]
- Papers
-
- ACIS Sub-pixel Resolution: Improvement in Point Source Detection (PDF), Anderson C S, Mossman A E, Kim D-W, Allen G E, Glotfelty K J & Fabbiano G, 2010, ADASS XX conference series
- Chandra ACIS Subpixel Event Repositioning: Further Refinements and Comparison between Backside- and Frontside-illuminated X-Ray CCDs (PDF), Li J, Kastner J, Prigozhin G, Schulz N, Feigelson E & Getman K, 2004, ApJ, 610, 1204
- Refining Chandra/ACIS Subpixel Event Repositioning Using a Backside-illuminated CCD Model (PDF), Li J, Kastner J, Prigozhin G & Schulz N, 2003, ApJ, 590, 586
- Improvement of the Spatial Resolution of the ACIS Using Split-Pixel Events (PDF), Tsunemi H, Mori K, Miyata E, Baluta C, Burrows D, Garmire G & Chartas G, 2001, ApJ, 554, 496
- Measurement of the subpixel structure of AXAF CCD's (PDF), Pivovaroff M, Jones S, Bautz M, Kissel S, Prigozhin G, Ricker G, Tsunemi H & Miyata E, 1998, IEEE Transactions on Nuclear Science, vol.45, No.2, pp. 164-175
Comments to cxccal (at) cfa.harvard.edu
