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Present Calibration Uncertainties

Absolute Spatial Positions

Calibration Observations: Mostly serendipitous targets.

Results: A large sample of Chandra observations of moderately bright point sources taken from launch through 10/07 was reprocessed with the updated alignment files released in May 2002 and May 2007. The update released in May 2007 corrects for thermal effects which affected observations taken between Nov 2006 and Jan 2007 when the aspect camera was cooled from -15 C to -19 C. The targets were selected based on the availability of accurate optical or radio positions from the Tycho2 or ICRS catalogs. Only sources within 3' of the optical axis were used for the comparison. This study showed that 90% of the sources had computed Chandra positions within 0.6" of their Tycho2 or ICRS positions and 99% had positions within 0.8" of their optical or radio positions. There are no time-dependent variations in the accuracy of the absolute astrometry but there are slight variations between the four focal plane detectors (see the memo noted below).

Related Memos: Chandra Absolute Astrometric Accuracy

Relative Absolute Spatial Positions

Calibration Observations: The open star cluster NGC2515, raster scans of ArLac and serendipitous targets.

Results: The open star cluster NGC2516 has been observed by all 4 focal plane detectors several times during the mission. The computed Chandra positions of the X-ray brightness stars in NGC2516 have been compared with their optical Tycho2 positions. For the ACIS detectors, the angular separations between the X-ray positions of the stars agree with the optical separations to 0.1" (1 σ). For the HRC-I detector, the relative positions agree to 0.3" (1 σ). The greater uncertainty in the HRC-I data probably arises from greater residuals in the image construction process.

Related Memos:2005 Calibration Workshop - An Improved HRC-I Degapping Correction

Focal Length, Plate Scale, and Relative Chip Positions

Absolute Energy Scale

Calibration Observations
TargetsDetector/GratingFrequency
External Calibration SourceACIS twice per orbit
E0102-72ACIS Semi-annual
Cas AACIS Semi-annual
CapellaLETG/HRC-S and HETG/ACIS-S annual

Results:

ACIS - During the first two weeks after the sunshade door on Chandra was opened and observations of the sky began, ACIS experienced significant radiation damage by soft protons focused onto the foal plane by the mirrors. The soft protons produced defects in the lattice structure of the CCDs. These defects delay the transfer of charge as events are clocked out and increase the charge transfer inefficiency (CTI) of the CCDs. CTI can reduce the gain of an event and also change the grade of an event. Since early in the mission, ACIS is stowed before each perigee passage to prevent excessive radiation damage. During this time, ACIS is fully illuminated by its external calibration source (ECS). Even with ACIS stowed during perigee passage, the particle background in the Chandra orbit produces a gradual increase in CTI at a rate of about 1.0% per year. Along with the ACIS observations of its external calibration source twice per orbit, a raster scan of the oxygen rich supernova remnant E0102-72 is carried out every year to monitor the low energy detector gain. The combination of these two sources allows the gain to be tracked over a broad range of energies. Since launch, the ACIS gain for each chip has been calibrated in 3 month intervals.

Since the release of CALDB 3.3 in Dec. 2006 there now exist a complete set of cti-corrected products for all 10 chips at a focal plane temperature of -120 C (the operating ACIS temperature since Jan. 2000). Using CIAO 3.4 or later, acis_process_events applies the appropriate time-dependent gain and cti-corrections by default. BI chips are corrected for both parallel and serial CTI. Based on the calibration products released in CALDB 3.3, the rms residuals in the gain are 0.3%. These residuals are nearly energy independent and spatially uniform across all 10 chips (see Fig. Residual Gain Errors and the 2005 calibration workshop report listed below).

Calibration Products
CALDB Files Description
acisD2000-01-29gain_ctiN0006.fitsCTI-corrected ACIS gain table

Related Memos: 2005 Calibration Workshop - CTI and Time Dependent Gain Corrections for ACIS

July 30, 2004 - Corrections for Time Dependence of ACIS Gains

2003 Calibration Workshop - Time-dependent Gain for ACIS

LETG - An updated version of the HRC-S de-gap coefficients table was released in CALDB 3.2.0 which has empirical wavelength corrections derived from multiple LETG/HRC-S observations of Capella. These observations were taken at a range of off-sets to cover a large portion of the HRC-S with bright emission lines of known energies. Based on these observations, the rms deviation between the known and computed wavelengths is 0.006 A on the central HRC-S plate, and 0.01 A across the entire HRC-S detector (see Fig. LETG dispersion)

Calibration Products
CALDB Files Description
hrcsleg1D1999-07-22lsfparmN0003.fitsLETG/HRC-S LRFs for positive orders
hrcsleg-1D1999-07-22lsfparmN0003.fitsLETG/HRC-S LRFs for negative orders
acissleg1D1999-07-22lsfparmN0003.fitsLETG/ACIS-S LRFs for positive orders
acissleg-1D1999-07-22lsfparmN0003.fitsLETG/HRC-S LRFs for negative orders

Related Memos: 2005 Calibration Workshop - HRC-S/LETG: Degap and Wavelength Corrections

2004 Calibration Workshop - Characterizing Non-linearities in the Chandra LETG+HRC-S Dispersion Relation

2003 SPIE - Characterizing the Non-Linearities in the Chandra LETG/HRC-S Dispersion Relation

2003 Calibration Workshop - The Dispersion Relation of the LETGS

2003 Calibration Workshop - Characterizing Non-linearities in the Chandra LETG+HRC-S Dispersion Relation

2003 Calibration Workshop - Degap Corrections for HRC-S Grating Observations

2003 Calibration Workshop - Amplifier Mis-match as a Possible Source of HRC Event

HETG - Based on a systematic analysis of multiple HETG/ACIS-S observations of Capella, the rms residual between the known and computed wavelengths for both MEG and HEG spectra is δ λ / λ = 1.0 X 10--4 (see Fig. HETG dispersion).

Calibration Products
CALDB Files Description
acismeg1D1999-07-22lsfparmN0005.fitsMEG/ACIS-S LRFs for positive orders
acismeg-1D1999-07-22lsfparmN0005.fitsMEG/ACIS-S LRFs for negative orders
acisheg1D1999-07-22lsfparmN0004.fitsHEG/ACIS-S LRFs for positive orders
acisheg-1D1999-07-22lsfparmN0004.fitsHEG/ACIS-S LRFs for negative orders

Related Memos: 2005 Measuring the Accuracy of Chandra/HETGS Wavelength Scale with Capella Data

Absolute Effective Area (Imaging)

Calibration Observations
TargetsDetector/GratingFrequency
ACIS external calibration sourceACIS twice per orbit
Cas A ACIS, HRCsemi-annual
E0102-72 ACISsemi-annual
G21.5-09 ACIS, HRCsemi-annual
HZ43 HRC-I semi-annual

Results:

HRMA (On-Axis Effective Area) - During ground-based testing at the XRCF, the absolute effective area of the mirrors was measured with emission line sources and continuum sources and with two different detectors (a gas proportional counter and a solid state detector). Extensive analyses of these data show that the systematic uncertainties in the absolute effective area of the HRMA are less than 3% at all energies (see Fig. On-Axis Area ). An updated version of the HRMA effective area was released in CALDB 3.2.1 that included a 22A layer of hydrocarbon contaminant on the mirrors. The contaminant increases the reflectivity of the mirrors near the Ir-M edge (2.2 keV) and corrects a problem with earlier versions of the HRMA effective area (see Fig. Ir-M Edge Residuals Eliminated).

HRMA (Off-Axis Vignetting) - The supernova remnant G21.5-09 was observed at 6 angles off-axis to test the predictions of the raytrace code regarding the vignetting of the mirrors. A comparison between the raytrace code and the G21.5-09 observations showed that the SAOSAC predictions are within 5% at energies below 6 keV and within 10 arcminutes of the optical axis. At higher energies and larger angles off-axis, the uncertainties can be as large as 10% (see the memo listed below).

Calibration Products
CALDB FilesDescription
hrmaD1999-07-22axeffaN0007.fitsOn-axis Effective area of the HRMA
hrmaD1996-12-20vignetN0003.fits Off-axis vignetting of the HRMA

Related Memos: 2005 Calibration Workshop - Improvements to the HRMA Effective Area

2003 SPIE - Chandra Observatory X-ray Mirror Effective Area

2003 Calibration Workshop - Chandra X-ray Observatory Mirror Effective Area

Measurement of Telescope Vignetting from G21.5-0.9 Off-axis Observations

HRC - The present version of the HRC-I QE is derived by fitting in-flight observations of G21.5-09, Cas A, and HZ43 to a model of the HRC-I QE derived from ground-based measurements. The blue shaded region in Fig. HRC-I QE shows the 1 σ uncertainty in the QE as a function of energy. The combined 1 σ uncertainties in the HRMA/HRC-I effective area are less than 7%. The uncertainties in the HRC-S QE are discussed in the gratings section.

Calibration Products
CALDB FilesDescription
hrciD1999-07-22qeN0007.fitsOn-axis HRC-I QE
hrciD1999-07-22qeuN0002.fitsQE map for the HRC-I
hrcsD1999-07-22qeN0009.fitsOn-axis HRC-S QE
hrcsD1999-07-22qeuN0004.fitsQE map for the HRC-S

Related Memos: 2004 Calibration Workshop - Status of the HRC

A New Flight Model of the HRC-I MCP Quantum Efficiency

An Update to the HRC-I MCP Quantum Efficiency Model

ACIS - The uncertainty in the absolute effective area of ACIS is a combination of the uncertainties in the ACIS QE near the read out, the QE uniformity (QEU) map, the depth of the contaminant on ACIS and the HRMA effective area. Uncertainties in the depth of the contaminant only affect the QE below approximately 2.0 keV. The contaminant is essentially transparent at higher energies. The ACIS QE at a given location on a given chip is computed from the ACIS QE at the read-out, which is unaffected by CTI, plus the spatial corrections contained in the QE map uniformity (QEU) map. The present version of the QEU map accounts for column-by-column variations in the QE due to the effects of CTI. The 1 σ uncertainties in the QEU are approximately 1% (see High-resolution QEU maps for ACIS-I and S1,2,3 chips). The cross-calibration uncertainties between the QEs of the FI and BI chips are less than 2% (see Absolute QE of ACIS S1, S2 and S3 from XRCF data at selected energies).

Periodic observations of the ACIS external calibration source and several astronomical objects show that there has been a continuous degradation in the low energy QE since launch due to the build-up of contaminant on the ACIS filters. The contaminant is thicker near the edges of the two ACIS detectors where the filters are colder ( see ACIS QE Degradation). This reference, along with those cited below, give detailed information regarding the chemical composition of the material, the time dependence of the contamination build-up and known spatial variations in the depth of the contaminant. A small correction was added in CALDB 3.3 to the QE of both BI and FI chips near the Si-K absorption edge, to account for the Si-K escape peak effect. This adjustment consists of a narrow 4% correction at 1800 eV.

Combining the 3% uncertainty in the absolute effective area of the HRMA along with the uncertainties in the ACIS QE, QEU and depth of the contaminant on the filter gives a 5% uncertainty in the absolute effective area of the ACIS detectors near the aim points (i.e., excluding the top and bottom 100 rows on ACIS-S and beyond a 6 arcminute radius on ACIS-I). Due to additional uncertainties in the depth of the contaminate near the edges of the detectors and mirror vignetting, the uncertainties at larger radii are approximately 10%.

Calibration Products
CALDB FilesDescription
acisD1997-04-17qeN0006.fitsACIS-I and ACIS-S QE near the read-out
acisD2000-01-29qeuN0002.fitsQE maps for ACIS-I and ACIS-S at T=-120
acisD1999-09-16qeuN0002.fitsQE maps for ACIS-I and ACIS-S at T=-110

Related Memos:Composition of the Chandra ACIS Contaminant

2004 Calibration Workshop - Improved High Spatial Resolution Calibration of ACIS QEU

2004 High-resolution QEU maps for ACIS-I and S1,2,3 chips

2004 Absolute QE of ACIS S1, S2 and S3 from XRCF data at selected energies

2003 Calibration Workshop - Absolute ACIS Quantum Efficiency

2003 Calibration Workshop - Time Dependence of the ACIS Contamination

2003 Calibration Workshop - Spatial Distribution of the Contaminant on the ACIS Camera

2003 Calibration Workshop - Composition of the Chandra ACIS Contaminant

Absolute Effective Area (Gratings)

Calibration Observations
TargetDetector/GratingFrequency
HZ43LETG/HRC-Ssemi-annual
PKS2155-304LETG/HRC-S, LETG/ACIS-S, HETG/ACIS-Ssemi-annual
3C273HETG/ACIS-Sannual
Sirius BLETG/HRC-S

Results:

LETG - The effective area of the LETG/HRC-S has been derived from XRCF data and observations of Sirius B, HZ43, PKS2155-304 and 3C273. The two white dwarfs strongly constrain the LETG/HRC-S effective area below 277 eV (44A), while the two AGN, along with ground based data, constrain the the effective area at higher energies. At the present time, most of the uncertainties in the LETG/HRC-S absolute effective area are due to uncertainties in the HRC-S QE. In CALDB 3.3, a new version of the HRC-S QE was released with a modified O-K edge structure for all three plates. This changed the QE near the O-K edge (545 eV) by approximately 10%. With the latest HRC-S QE, the uncertainties in the LETG/HRC-S 1st order absolute effective area are less than 15% at all energies. This 15% includes the uncertainties in the absolute HRMA effective area, HRC-S QE, HRC-S QEU and the first order LETG transmission efficiency. The transmission efficiency of the higher orders have an uncertainty of 10% relative to the first order, which gives an uncertainty in the LETG/HRC-S absolute effective area of the higher orders of 20%.

Calibration Products
CALDB FilesDescription
letgD1996-11-01greffpr001N0005.fitsLETG Efficiency for all orders

Related Memos: LETG+HRC-S Effective Area memo

2004 Calibration Workshop - Improvements to the HRC-S QE uniformity and LETGS effective area

Chandra LETG Higher Order Diffraction Efficiencies

2002 SPIE - In-Flight Effective Area Calibration of the Chandra LETG

HETG - With the release of CALDB 3.2.1, the cross-calibration uncertainties between the HEG and MEG are less that 5% at all energies (see the memo listed below). With the latest calibration files, the uncertainties in the HETG/ACIS-S 1st order absolute effective area are less than 8% at all energies. This includes uncertatinties in the absolute HRMA effective area, the ACIS QE, QEU and the 1st order HETG transmission efficiency.

Calibration Products
CALDB Files Description
hetgD1996-11-01greffpr001N0005.fitsMEG and HEG efficiencies for all orders

Related Memos: 2005 Calibration Workshop - HETGS Effective Area Updates

2004 Calibration Workshop - Overview of the HETGS Calibration

High Energy Transmission Grating Spectrometer Calibration

Energy Resolution

Calibration Observations
TargetsDetector/GratingFrequency
External Calibration SourceACIS twice per orbit
E0102-72ACIS annual
Cas AACIS annual
CapellaLETG/HRC-S and HETG/ACIS-S annual

Results:

ACIS Analysis of ACIS data has shown that the spectral response of ACIS is best computed in a two step process. After the data is cti-corrected and the time-dependent gain corrections are applied, the response at a given position on a given chip can be computed from the response of a pristine chip (i.e., a chips with zero CTI) and an extrapolation that adjusts the response to a given position on a given chip. The response of all 10 chips are calibrated in 32 by 32 pixel regions through an analysis of external calibration source data and observations of astronomical sources, primarily, E0102-72. With the release of CALDB 3.3, all 10 chips have a complete set of cti-corrected calibration products for data acquired at a focal plane temperature of T=-120 C. Both parallel and serial cti-corrections are applied to data on the BI chips S1 and S3. Response matrices can be generated with these cti-corrected calibration products using the CIAO task mkacisrmf. The residuals between the measured FWHM of emission lines and the predictions using cti-corrected calibration products in CALDB 3.3 are approximately 20eV. The residuals in the FWHM are fairly independent of energy and chip location.

Calibration Products
CALDB Files Description
acisD1999-09-16fef_phaN0002.fitsACIS spectral response at T=-110C (uncorrected for CTI)
acisD2000-01-29fef_phaN0005.fitsACIS spectral response at T=-120C (uncorrected for CTI)
acisD2000-01-29p2_respN0006.fitscti-correction matrix for T=-120C
acisD2000-01-29ctiN0006.fitsACIS spectral response for T=-120C (corrected for CTI)

Related Memos: 2005 ACIS Energy Response Performance with the External Calibration Source

2003 Calibration Workshop - A New Paradigm for the Generation of ACIS Response Matrices

HETG -The LSFs of the HETG and LETG are generated by fitting parametric functions to simulated MARX spectra. The modeled LSFs are then validated with gratings observations of Capella taken at several angles off-axis. The HEG and MEG LSFs are fit with two gaussians and two Lorentzians at each energy. A recent study showed that the 1 σ uncertainties in the FWHM of the lines are 0.00064A for the MEG and 0.00035A for the HEG, with little energy dependence between 0.8 and 6.0 keV. The minimum FWHM for MEG spectra is 0.017A and occurs between 5-12A. The minimum FHWM for HEG spectra is 0.008A and occurs between 3-8A (see Fig. FWHM of HETG Spectra). The relative uncertainties in the FWHM are thus less than 4% for MEG spectra and less than 5% for HEG spectra.

Calibration Products
CALDB Files Description
acismeg1D1999-07-22lsfparmN0005.fitsMEG/ACIS-S LRFs for positive orders
acismeg-1D1999-07-22lsfparmN0005.fitsMEG/ACIS-S LRFs for negative orders
acisheg1D1999-07-22lsfparmN0004.fitsHEG/ACIS-S LRFs for positive orders
acisheg-1D1999-07-22lsfparmN0004.fitsHEG/ACIS-S LRFs for negative orders

Related Memos: LSF Verification: Capella HETG/ACIS-S

Exercising the Chandra Grating Line Response Functions

LETG - Similar to the HETG, the LSFs for LETG/HRC-S spectra are generated by fitting parametric functions to simulated MARX spectra. A recent comparison of these models with a set of Capella observations taken at different angles off-axis shows that the uncertainties in the FWHM are less than 20% at all energies. The uncertainties in the FWHM of LETG/HRC-S spectra are most likely dominated by uncertainties in the HRC-S de-gap map at the 1 to 2 pixel level. More detailed information about HRC-S spatial nonlinearities can be found in the memos listed under the LETG absolute energy section above.

Calibration Products
CALDB Files Description
hrcsleg1D1999-07-22lsfparmN0003.fitsLETG/HRC-S LRFs for positive orders
hrcsleg-1D1999-07-22lsfparmN0003.fitsLETG/HRC-S LRFs for negative orders
acissleg1D1999-07-22lsfparmN0003.fitsLETG/ACIS-S LRFs for positive orders
acissleg-1D1999-07-22lsfparmN0003.fitsLETG/HRC-S LRFs for negative orders

Relative Efficiency

Calibration Observations
TargetsDetector/GratingFrequency
ACIS external calibration sourceACIS twice per orbit
E0102-72 ACISsemi-annual
Raster scans of ArLac HRC-I and HRC-S semi-annual
PKS2155-304 LETG/HRC-S and LETG/ACIS-S semi-annual
3C273 HETG/ACIS-S annual

Results:

ACIS - There are two primary factors that affect the spatial uniformity of the QE on the CCDs: 1) variations in the depth of the contaminant on the ACIS filters, and 2) CTI which causes good grades to migrate into bad grades. The first factor only affects photon energies below 2~keV, while the second factor produces an energy independent decrease in QE with increasing chipy (parallel to the read-out direction). Flight event grades (which vary from 0 to 255) can be categorized as good-good or good-bad. Good-good flight grades (flt grades 0,8,16,64,72,80,104,208) are valid events that migrate into valid ASCA grades. Good-bad flight grades (2,10,11,18,22) are valid events that migrate into bad ASCA grades. The QE of good-good flight grades is very flat, while there are significant column to column variations in the QE of good-bad flight grades. With CIAO 3.1, the column-to-column variations in the QE of good-bad flight grades are taken into account. The spatial variation in the depth of the contaminant is also properly taken into account in CIAO 3.2.

CALDB Products:
CALDB ProductsDescription
acisD2000-01-29qeuN0006.fitsQE maps for ACIS-I and ACIS-S at T=-120
acisD1999-09-16qeuN0002.fitsQE maps for ACIS-I and ACIS-S at T=-110

Related Memos: 2003 Calibration Workshop - Absolute ACIS Quantum Efficiency

2003 Calibration Workshop - Spatial Distribution of the Contaminant on the ACIS Camera

HRC - Spatial variations in the QE of the MCPs were measured with ground-based flat field tests. These data sets were then used to derive the HRC-I and HRC-S QE maps. A series of 40 observations of Capella were taken at different locations on the HRC-I from 2006 through 2007. These observations were used to update the de-gap coefficients of the HRC-I and improve image reconstruction. Using the present version of the HRC-I QE map and accounting for intrinsic variations in the X-ray flux of Capella during these observations, the rms scatter in corrected count rates is approximately 1% accross the HRC-I.

CALDB Products:
CALDB ProductsDescription
hrciD1999-07-22qeuN0003.fitsHRC-I QE Map
hrcsD1999-07-22qeuN0004.fitsHRC-S QE Map

Related Memos: 2007 Calibration Workshop - Verifying the HRC-I QE and QE Uniformity

HRC Flat Field Maps

LETG - The in-flight effective area of the LETG/HRC-S has been derived from observations of Sirius B, HZ43, PKS2155-304, and 3C273. The two white dwarfs strongly constrain the LETG/HRC-S effective area below 277 eV (44A), while the two AGN constrain the shape of the effective area at higher energies. The rms scatter in the residuals on the scales of 0.05A between the modeled spectra of these four objects and the data is approximately 6%.

Related Memos: 2004 - Improvements to the HRC-S QE uniformity and LETGS effective area

2002 SPIE - In-Flight Effective Area Calibration of the Chandra LETG

HETG - The in-flight effective area of the HETG/ACIS-S has been derived using the same sources as that used for the LETG/HRC-S. At present, all residuals between the modeled spectra and data for these sources are less than 5% at all energies.

Related Memos: 2005 Calibration Workshop - HETGS Effective Area Updates

Point Spread Function

Calibration Observations
TargetDetector/Grating
ArLacHRC-I
3C273 HRC-I, ACIS-S
HR1099 HRC-I, ACIS-I
Her X-1 ACIS-S
RE J1032+53 HRC-I
LMC X-1 HRC-I, ACIS-I, ACIS-S
serendipitous targets.HRC-I, ACIS-I, ACIS-S

Results:

On-Axis PSF - A high fidelity raytrace code (SAOSAC) that simulates the performance of the Chandra mirrors (HRMA) has been in development since long before launch. The raytrace code was fine tuned before launch based on extensive measurements of the imaging properties of the HRMA at the XRCF at MSFC. A recent comparison between SAOSAC simulations and a long HRC-I observation of Ar-Lac shows that the residuals in the on-axis PSF between the raytrace code and the data are less than 10% within 2.0" of the image centroid (see Fig. On-Axis HRC PSF ). The residuals between SAOSAC simulations and point sources observed with ACIS are slightly larger (see Fig. On-Axis ACIS PSF ). Also, the residuals with the ACIS PSF are not azimuthally symmetric. There appears to be an elongation in the ACIS PSF toward the read-out direction (see Fig. ACIS Imaged Point Source). The larger residuals in the ACIS PSF are most likely due to the imaging properties of ACIS which is presently under investigation. The same version of the raytrace code was used to generate the HRMA PSF library available in CIAO (see the CALDB products listed below) so users should expect the same accuracy in the PSF library. There is also a web based interface ( ChaRT ) for running SAOSAC raytrace simulations.

PSF Wings - There is so little power in the HRMA PSF scattered beyond 10 arcseconds, that it is not practical to populate the wings of the PSF with a sufficient number of photons when generating the PSF library. To determine the wings of the PSF, we observed Her X-1 for 50 ksec with ACIS-S and found that the wings are well represented by analytic functions (see the memos below). Fig. PSF-wings shows an example of the best-fit analytic function to the wings of the HRMA PSF in two different energy bands.

Off-Axis PSF - The Chandra PSF varies considerable with source position and energy. Off-Axis images are roughly elliptical with position angles and ellipticities that not only depend on the off-axis angle of the source, but also the azimuthal angle of the source (see Fig. Off-Axis Images for some examples). We have found that the off-axis PSF can be parameterized by the ECF (Enclosed Count Fraction), i.e., the fraction of the total counts within a given ellipse. The ECF is analogous to the encircled energy for azimuthally symmetric images. The ECF has been calibration based on a large suite of raytrace simulations of point sources at different angles-off axis, azimuths, and photon energies. Tables have been generated that give the best-fit values of the semi-major axis, ellipticity, and position angle of an ellipse that encloses a certain fraction of the total counts as a function of source position and energy. The residuals between the tabulated ECF values and a sample of HRC-I observations of point sources are less than 5% (see Fig. ECF Comparison)

Calibration Products
CALDB FilesDescription
acisi1998-11-052dpsf1N0002.fitsMedium resolution ACIS-I images
acisi1998-11-052dpsf2N0002.fitsLow resolution ACIS-I images
acisi1998-11-052dpsf3N0002.fitsHigh resolution ACIS-I images
acisi1998-11-052dpsf4N0002.fitsHighest resolution ACIS-I images
aciss1998-11-052dpsf1N0002.fitsMedium resolution ACIS-S images
aciss1998-11-052dpsf2N0002.fitsLow resolution ACIS-S images
aciss1998-11-052dpsf3N0002.fitsHigh resolution ACIS-S images
aciss1998-11-052dpsf4N0002.fitsHighest resolution ACIS-S images
hrci1998-11-052dpsf1N0002.fitsMedium resolution HRC-I images
hrci1998-11-052dpsf2N0002.fitsLow resolution HRC-I images
hrci1998-11-052dpsf3N0002.fitsHigh resolution HRC-I images
hrci1998-11-052dpsf4N0002.fitsHighest resolution HRC-I images
hrcs1998-11-052dpsf1N0002.fitsMedium resolution HRC-S images
hrcs1998-11-052dpsf2N0002.fitsLow resolution HRC-S images
hrcs1998-11-052dpsf3N0002.fitsHigh resolution HRC-S images
hrcs1998-11-052dpsf4N0002.fitsHighest resolution HRC-S images
Note:For a more detailed description see Summary of the Chandra PSF Library

Related Memos: 2003 SPIE - Calibration of Chandra's Near On-Axis Performance.

2003 SPIE - A Parameterization of the Chandra Point Spread Function

2003 Calibration Workshop - Calibration of Chandra's Near On-axis PSF

2003 Calibration Workshop - Calibrating the Wings of the Chandra PSF

2003 Calibration Workshop - A Parameterization of the Chandra Point Spread Function

2004 Analysis of PSF Wings

Relative Time Precision

Calibration Observations: Crab pulsar

Results:A wiring error in the HRC causes the arrival time of an event to be assigned to the following event, which may or may not be telemetered due to telemetry saturation or a high probability that the event is a charged particle. An HRC timing mode has been developed that only reads out the central segment of the HRC-S. For sources that do not exceed the telemetry limit of 180 cts/s (source plus background), the relative times are precise to within 4 to 18 mu s.

2003 Calibration Workshop - Clock Correlation Contribution to Chandra Timing Accuracy

Barycentric Time Accuracy

Calibration Observations: Crab pulsar

Results:

HRC-S Analysis of a long HRC-S observation of the Crab pulsar in timing mode shows that the uncertainty in the barycentric times are 35us.

Related Memos: 2003 Calibration Workshop - Astronomical Calibration of the Chandra Clock

Discovery of X-Ray Emission From the Crab Pulsar at Pulse Minimum

ACIS-CC The absolute time accuracy in ACIS-CC mode observations is primarily limited by the absolute accuracy of the aspect solution. A one pixel (0.5 arcsecond) uncertainty in the aspect solution of a photon corresponds to an uncertainty of 2.85 msec in the absolute arrival time of that photon in CC mode read-out. A script has been written which is available through the memo references, that interpolates the event times in CC mode. Applying this script to an ACIS-CC mode observation of the Crap pulsar yielded errors of 1.5 msec.

Related Memos: ACIS CC mode absolute time




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