Abstracts from the Chandra Calibration Workshop

Title: LETG Higher Order Diffraction Efficiency Final Results
Authors:Brad Wargelin (SAO)
Presenter: Brad Wargelin
Presentation Type: Oral
Abstract: Accurate calibration of the Chandra Low Energy Transmission Grating (LETG) higher-order (|m|>1) diffraction efficiencies is vital for proper analysis of spectra obtained with the LETG´s primary detector, the HRC-S, which lacks the energy resolution to distinguish different orders. Pre-flight ground calibration of the LETG was necessarily limited to sampling a relatively small subset of spectral orders and wavelengths, and results from those measurements have defied attempts to create a single self-consistent theoretical model that matches the data for all orders. We have recently completed an analysis of diffraction efficiencies based on in-flight data obtained using the LETG´s secondary detector, the ACIS-S array, utilizing its energy resolution to separate orders. We present our results, which were released in August 2004 in CALDB 2.28.
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Title: Improvements to the HRC-S QE uniformity and LETGS effective area
Authors: Deron Pease (SAO/CXC), Jeremy Drake (SAO/CXC)
Presenter: Deron Pease
Presentation Type: Oral
Abstract: We present the in-flight calibration that has led to recent improvements in the HRC-S QE uniformity (QEU). We achieve this through high signal-to-noise LETG/HRC-S observations of AGN and white dwarfs. The QEU calibration is performed semi-independently from other telescope effective area model components. The new QEU, along with the updated LETG higher order efficiencies and HRMA effective area models (each presented earlier in this workshop), is then applied to derive improved HRC-S QE and effective area, particularly optimized for use with the LETG/HRC-S.
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Title: Investigating the Chandra Transmission Grating Spectrometer Line Response Functions
Authors: Jeremy Drake (SAO/CXC), Sun Mi Chung (SAO/CXC), Vinay Kashyap (SAO/CXC), Peter Ratzlaff (SAO/CXC)
Presenter: Jeremy Drake
Presentation Type: Oral
Abstract: HETG and LETG spectra of narrow-line point sources have been used to investigate the instrument line response functions (LRFs). The propriety of synthetic LRFs generated based on ray-trace simulations will be evaluated, and the relevance of the LRF and its calibration to scientific analysis will be discussed.
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Title: The Chandra View of X-ray Binaries
Authors:
Presenter:
Presentation Type: Oral
Abstract:
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Title: Overview of the HETGS Calibration
Authors: Herman Marshall (MIT CSR)
Presenter: Herman Marshall
Presentation Type: Oral
Abstract: I will give an overview of the HETGS calibration progress over the last year. Most of the changes to the HETGS effective area relate to the ACIS quantum efficiency and the contaminant. There is a new QE model that should reduce systematic errors near 500 eV and the model of the ACIS contaminant is good to better than 10% for HETGS data. The dispersion relation will be reexamined after one more adjustment of the ACIS chip positions and rotations. The main upcoming work involves systematic cross-checking with other X-ray telescopes such as XMM and Astro-E2.
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Title: Constraints on higher orders using Sco X-1
Authors: Norbert S. Schulz (MIT), and the MIT/HETG team
Presenter: Norbert S. Schulz
Presentation Type: Oral
Abstract: Using Sco X-1 and other bright X-ray sources we review contraints in the use of higher order spectra obtained with the HETG. Higher order spectra, though of lower efficiency and thus reasonably accessible for only bright X-ray sources, offer substantially increased resolving power.
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Title: Status of ACIS background
Authors: Maxim Markevitch (SAO)
Presenter: Maxim Markevitch
Presentation Type: Oral
Abstract: I will review the current calibration status and trends of the ACIS background. I will also give an example of analysis of a galaxy cluster in the presense of complications such as flares and Galactic excess.
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Title: Back-Illuminated ACIS QE: Revised.
Authors: Richard Edgar (SAO)
Presenter: Richard Edgar
Presentation Type: Oral
Abstract: Ground calibration data from the X-ray Calibration Facility (XRCF) at Marshall Space Flight Center are presented. A new analysis shows that the absolute Quantum Efficiency (QE) as of the time of the Chandra Observatory launch for the back illuminated devices (S1 and S3) was underestimated in earlier CALDB releases.

There are two reasons for this underestimate: the model of the CCD devices that was used had an error, which decremented the low-energy QE. Also, there was a misunderstanding about the definition of the QE Uniformity factor (QEU maps). This latter effect impacts the BI chips at high energies, where their non-trivial charge transfer inefficiency (CTI) at launch causes events to be lost.

Note that these effects are independent of any post-launch changes in ACIS QE due to contamination or changes in CTI.

The products described here were released in August of 2004 with CALDB release 2.28. This work was supported by the Chandra X-ray Science Center under NASA contract NAS8-39073.
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Title: Improved high spatial resolution calibration of ACIS QEU
Authors: Alexey Vikhlinin (SAO)
Presenter: Alexey Vikhlinin
Presentation Type: Oral
Abstract: ECS data accumulated over several years of ACIS operations show the small-scale variations of the quantum effciency - intra-node variations in the FI CCDs and strong column-to-column fluctuations in the BI chips. We report on creation of new high-resolution quantum effciency non-uniformity maps (QEU) for ACIS-I and 3 CCDs in ACIS-S (S1, S2, and S3). This new calibration reduces the QEU uncertainties to 1%-2% from the present 5%.
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Title: Evolution of ACIS Performance
Authors: Catherine Grant (MIT)
Presenter: Catherine Grant
Presentation Type: Oral
Abstract: Over the lifetime of Chandra, the performance of ACIS continues to evolve. I will present the history of ACIS detector characteristics, such as gain and charge transfer inefficiency, to the present time and discuss expectations for the future. I will also describe, in general terms, how this evolution affects science data calibration.
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Title: CTI and time dependent gain corrections for ACIS
Authors: Norbert S. Schulz (MIT), and the CXC/ACIS calibration team
Presenter: Norbert S. Schulz
Presentation Type: Oral
Abstract: The CCD of the ACIS detector are subject to time dependent changes in detector response. These changes are continuously monitored with external calibration sources before and after Chandra earth radiation zone passages. The charge transfer inefficiency (CTI) of the devices results in a slow but persistent drift in the detector gain. The modeling of the spatial distribution of CTI specifically in FI devices is done by constructing trap maps, the time dependent gain drift though the "tgain" algorithm for all devices. Both corrections are now available in the standard CXC software distribution (CIAO) for most devices. We describe method and status of these corrections.
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Title: Diagnosing the ACIS Contaminant using Grating Observations
Authors: Herman Marshall (MIT CSR)
Presenter: Herman Marshall
Presentation Type: Oral
Abstract: I will summarize results from the analysis of Chandra grating spectra relating to the characterization of the ACIS contaminant. The work of the last year is highlighted by two observations of Mk 421 that were taken within one day of each other but at two different locations on the detector. Of the many results that can be obtained from these data are 1- O and F are clearly present in the additional material near the readout rows, 2- we can place limits on the composition gradient across the detector, 3- we can measure the gradient of the contaminant thickness as the telescope dithers, and 4- we can measure this gradient near row 175 as a function of time. Results will be compared to the optical depths determined from the external calibration source.
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Title: Spatial structure of the ACIS contamination from the ECS analysis
Authors: Alexey Vikhlinin (SAO)
Presenter: Alexey Vikhlinin
Presentation Type: Oral
Abstract: We summarize measurements of the spatial and time dependence of the effective contamination optical depth for the L-complex in the ECS spectrum. The developed model results in ~<5% uncertainties in the contamination corrections of the effective area at 0.6-0.7 keV and < 3% uncertainties at higher energies across both ACIS-S and ACIS-I arrays.
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Title: Prospects for an ACIS Bakeout
Authors: Paul Plucinsky (SAO)
Presenter: Paul Plucinsky
Presentation Type: Oral
Abstract: We will discuss the prospects for a bakeout of the ACIS instrument to remove the layer of contamination which has been degrading the low-energy detection efficiency. We will review the data from the ground tests of flight spare optical blocking filters. We will review the results of the efforts to model the effectiveness of the proposed bakeout. We will discuss the implications of the possible changes in the instrument performance after the bakeout.
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Title: Empirical Corrections to the HRMA Ir M Edge Discrepancy
Authors: Diab Jerius (SAO), Herman Marshall (MIT)
Presenter: Diab Jerius
Presentation Type: Oral
Abstract: Dispersed spectra of continuum sources exhibit an apparent residual edge at the iridium M edge near 2.1 keV. The edge can be modeled empirically as a reverse absorption edge (i.e. negative optical depth above 2.1 keV) with an amplitude of about 5%. The edge can be confused with the effect of pileup at the peak of the grating spectrometers´ efficiency curves;; a detailed examination of low flux continuum sources has been used to provide an empirical correction for this effect. The most likely explanation for the feature is a thin contaminant layer on the mirrors.
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Title: Revisiting Iridium Optical Constants and the Chandra HRMA Effective Area
Authors: Dale E Graessle (CXC), Diab Jerius (CXC), Regina Soufli (Lawrence Livermore), Art J Nelson (Lawrence Livermore), Eric M Gullikson (Lawrence Berkeley)
Presenter: Dale E Graessle
Presentation Type: Oral
Abstract: In response to the CUC initiative concerning the disposition of the iridium M-edges in the HRMA effective area, we have refined the optical constants of Ir as derived from the synchrotron reflectance data. At issue were the uncertainties in the derived constants in the M-edge region and the influence and validity of the presumed overlayer in the model. We have additional X-ray measurements of the overlayer composition on two Chandra witness mirrors, from X-ray photoelectron spectroscopy carried out at Lawrence Livermore National Laboratory in the Summer of 2004. Note that these overlayer measurements are germane to the witness mirrors only (not the HRMA). The measurements indicate multiple molecular components in the overlayer which include C, N, O (in molecular combinations), a trace of Si, and IrO. We have constructed a single overlayer to include these elements in atomic form in similar concentrations. We fitted reflectance versus angle scans with the overlayer thickness as a free parameter. We then refitted for optical constants versus energy as in our previous work. These optical constants are in final form for publication and possible inclusion in the Atomic Data Tables of Henke, Gullikson, et al. In addition we have used them to recalculate the HRMA effective area versus energy from the standard Chandra raytrace code. We compare this with the previous effective area, and address the influence the new results will have on the M-edge residuals investigated by H.L. Marshall et al.(this conference).
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Title: Chandra Telescope Optical Axis
Authors: Ping Zhao (SAO)
Presenter: Ping Zhao
Presentation Type: Oral
Abstract: Telescope Optical Axis (TOA) is one of the most important parameters of the Chandra X-ray Observatory. During normal operation, one of the four (ACIS-I, ACIS-S, HRC-I or HRC-S) aimpoints is positioned near the TOA. By definition, the center of each detector is located on the TOA. The determination of the TOA is one of the on-orbit calibration tasks. Since the Chandra launch, the position of TOA has been continuously monitored. About once a year, a raster scan of off-axis observations of a bright point source (HR1099 or AR Lac) was conducted. The results are used to calculate the TOA position. We analyze all the raster scan data obtained in the past 5 years, determine the TOA position for each time period and examine if there were any drift in the TOA.
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Title: The HRMA User's Guide
Authors: Terrance Gaetz (SAO), Diab Jerius (SAO)
Presenter: Terrance Gaetz
Presentation Type: Oral
Abstract: Understanding the optical performance of the Chandra Observatory can be a daunting undertaking, given its complex behavior. To provide some guidance to the general observer, we have created a "HRMA User's Guide", which collects in one place our knowledge of the optics´ properties and foibles, with particular emphasis on those features which may affect the interpretation of imaging data.
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Title: Chandra Observations of Kiloparsec-Scale Jets
Authors:
Presenter: Dan Schwartz
Presentation Type: Oral
Abstract:
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Title: Overview of HRC Performance
Authors: R. Hank Donnelly (CXC/SAO), Jennifer Posson-Brown (CXC/SAO), Michael Juda (CXC/SAO), Charles Wilton (CXC/SAO), Deron Pease (CXC/SAO)
Presenter: R. Hank Donnelly
Presentation Type: Oral
Abstract: We present a brief summary of the current state of the understanding of the performance of the HRC in imaging mode. We will cover evolution in the gain/pha response and the decision to not adjust the voltage as well as updates on the QE uniformity results at low energies and other topics of interest.
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Title:
Authors:
Presenter: Vadim Burwitz
Presentation Type: Oral
Abstract:
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Title: Chandra and Newton: Common Low-Energy Grating Observations
Authors: Vinay Kashyap (CXC/SAO), Jeremy Drake (CXC/SAO), Sun Mi Chung (CXC/SAO)
Presenter: Vinay Kashyap
Presentation Type: Oral
Abstract: We present a progress report on comparing objects observed with both Chandra and XMM-Newton, with an emphasis on sources observed with the Low-Energy Transmission Grating Spectrometer (LETGS) and the Reflection Grating Spectrometer (RGS). There are several candidates for such an analysis, and here we will concentrate on bright coronal X-ray sources such as Capella (alpha Aur;; G8III+G1III), whose emission is characterized by a high-temperature thermal spectrum with strong emission lines, and which has been observed simultaneously with both Chandra/HRC-S+LETG and XMM-Newton/RGS. We measure fluxes from lines common to both instruments and compare them. We will also explore the effects on spectral parameters, codified for example in emission measure distributions.
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Title: Chandra/XMM cross-calibration: Temperatures and soft X-ray fluxes of four galaxy clusters with ACIS-S/EPIC
Authors: Max Bonamente (NASA/NSSTC)
Presenter: Max Bonamente
Presentation Type: Oral
Abstract: Calibration of the ACIS quantum efficiency (QE) and contaminant are crucial for measuring cluster temperatures and soft X-ray fluxes (E< 1keV). I assess the performances of the current calibration by analyzing data of 4 galaxy clusters (Coma, A1795, A3112 and AS1101) observed with ACIS-S and. I compare temperatures and soft X-ray fluxes using the latest calibration data (CALDB 2.28), the earlier QE calibration data (CALDB 2.26) and XMM/EPIC data for the same clusters. The Chandra and XMM results are not in agreement, with Chandra typically measuring higher T than XMM, and measuring lower soft X-ray fluxes than XMM.
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Title: XMM-Newton (cross) calibration
Authors: Marcus Kirsch (ESA)
Presenter: Marcus Kirsch
Presentation Type: Oral
Abstract: ESA´s large X-ray space observatory XMM-Newton is in its fifth year of operations. We give a general overview of the status of calibration of the five X-ray instruments and the Optical Monitor. A main point of interest in the last year became the cross-calibration between the instruments. A cross-calibration campaign started at the XMM-Newton Science Operation Centre at the European Space Astronomy Centre in collaboration with the Instrument Principle Investigators provides a first systematic comparison of the X-ray instruments EPIC and RGS for various kind of sources making also an initial assessment in cross calibration with other X-ray observatories.
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Title: Overview talk
Authors:
Presenter: Larry David
Presentation Type: Oral
Abstract:
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Title: A measurement of the HRMA vignetting with Abell 1795
Authors: Eli Beckerman (SAO), Diab Jerius (SAO)
Presenter: Eli Beckerman
Presentation Type: Poster
Abstract: We extend our calibration of the as-measured vignetting of the focal plane by the Chandra optics by analyzing an off-axis pointing of A1795, a galaxy cluster. The observation yielded data which are relatively bright, yet not piled up. Earlier measurements of telescope vignetting using G21.5-0.9 are complicated by pileup. We have performed a sensitivity analysis to determine the effect of the extended nature of A1795 on measurements of the vignetting. We present the results of this analysis as well as the determined vignetting value in the context of our previous findings.
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Title: Characterizing Non-linearities in the Chandra LETG+HRC-S Dispersion Relation
Authors: Sun Mi Chung (CfA), Jeremy Drake (CfA), Vinay Kashyap (CfA), Peter Ratzlaff (CfA), Brad Wargelin (CfA)
Presenter: Sun Mi Chung
Presentation Type: Poster
Abstract: The dispersion relation for the Chandra Low Energy Transmission Grating Spectrometer (LETGS) is currently calibrated down to a Root-Mean-Square (RMS) value of 0.014~\AA, over the wavelength range of 5-150~\AA. In the last year we have corrected a wavelength discontinuity observed in the dispersion relation of the LETGS between the central and outer plates of the HRC-S detector, by changing the effective plate gap sizes of the HRC-S. However, there are still non-linear deviations in the positions of some lines by as much as 0.05~\AA. These deviations are thought to be caused by spatial non-linearities in the imaging characteristics of the HRC-S detector. Here, we present methods used to map out the wavelength non-linearities across the detector, as well as an empirical correction which reduces the observed wavelength non-linearities in the central plate by a factor of 2 or more.
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Title: Chandra HRC-S Degapping Corrections from Flight and Lab Data
Authors: Vinay Kashyap (CXC/SAO), Jeremy Drake (CXC/SAO)
Presenter: Vinay Kashyap
Presentation Type: Poster
Abstract: The HRC-S is primarily used for spectroscopic observations with the Low Energy Transmission Grating Spectrometer (LETGS) in place. Photons are detected via signals read out from evenly spaced wires underneath the plates and positions are computed by centroiding around the strongest amplifier signals. This process leads to gaps in between the taps where no events are placed. A deterministic correction is then made during ground processing to these event locations to remove the gaps. We have now developed a new, empirical degap corrections from analyzing flight data and compare them with degap corrections derived from a re-analysis of lab data. We compute polynomial fit coefficients that can be used in CALDB correction files.
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Title: Studying the HRC-I Uniformity with Observations of the Vela SNR
Authors: Jennifer Posson-Brown (SAO/CXC), R. Hank Donnelly (SAO/CXC)
Presenter: Jennifer Posson-Brown
Presentation Type: Poster
Abstract: While the nominal QEU map shows that above 183 eV the HRC-I is uniform across the detector to within +/- 10%, repeated observations of HZ 43 have revealed a significant depression from the expected QE at +10´ off-axis. To investigate this, we have used two observations of the Vela SNR taken with the HRC-I at opposite roll angles to create a ratio image that is a relative measure of the detector response. This ratio image indicates that the detector is flat to within +/- 10%, in good agreement with the nominal QEU map. The depression at +10´ off-axis is not seen in the ratio map, indicating that it does not affect the detector´s performance above 150 eV.
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Title: A DS9-based Interface to HRMA Enclosed Count Fractions Files
Authors: Francis A. Primini (SAO)
Presenter: Hank Donnelly
Presentation Type: Poster
Abstract: Recently released HRMA calibration files, based on the SAOsac model of the Chandra PSF, describe the Enclosed Count Fraction vs. distance from PSF center for both circular and elliptical apertures in a 3-D grid of off-axis angle (theta, phi) and energy (see http://cxc.harvard.edu/cal/Hrma/psf/index.html). The files´ organization is well-documented in the on-line help files, but users may find the data difficult to access without developing their own software. We have done so, and present a software package that is launched from DS9. With it, users may display Chandra images or event lists, define one or more regions of interest, and retrieve ECF information for those regions.
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Title: Chandra Automated Point Source Processing for Calibration Monitoring
Authors: Brad Spitzbart (SAO), Scott Wolk (SAO)
Presenter: Brad Spitzbard
Presentation Type: Poster
Abstract: We have developed a system to automatically analyze Chandra x-ray observations of point sources for use in monitoring telescope parameters such as point spread function, spectral resolution, and pointing accuracy, as well as for use in scientific studies. The Chandra archive currently contains at least 50 observations of stellar cluster-like objects, yielding 10,000+ sources of all spectral types well-suited for cataloging. The system incorporates CIAO tools, Acis_extract (Penn State), and YAXX (SAO) pipelines. Our software contribution comes in compiling the final results, merging in data from other catalogs, formatting text and XML output for web display, and developing back-end tools for analysis. We will outline this processing pipeline design and challenges and focus on its role in monitoring on-orbit observatory performance.
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Title: The AXAF Guide/Aspect Star Catalog (AGASC) Version 1.6
Authors: Brett Unks (SAO/CXC), Tom Aldcroft (SAO/CXC), Rob Cameron (SAO/CXC)
Presenter: Brett Unks
Presentation Type: Poster
Abstract: Version 1.6 is the third on orbit calibration of the AGASC. Using more than 30000 aspect camera star observations from over the course of the Chandra mission we are able to calculate the ACA (Aspect Camera Assembly) response to a much higher precision and over a broader band of star colors than previous calibrations. AGASC 1.5 was deemed to require improvement for Chandra flight operations after the discovery of a offset of up to 0.5 mags between the predicted AGASC magnitude and the observed ACA magnitude for red stars with a Tycho-2 color greater than 0.9. Here we present the calibration details of AGASC 1.6 and show the improvement over previous catalogs.
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