Abstracts from the Chandra Calibration Workshop

Title: Calibration of Chandra's Near On-axis PSF
Authors: Diab Jerius (SAO), Terrance Gaetz (SAO), Margarita Karovska (SAO)
Presenter: Diab Jerius
Presentation Type: Oral
Abstract: The Chandra X-Ray telescope has excellent angular resolution for on-axis sources. The Chandra PSF was first characterized during ground calibration and, most recently, from actual on-orbit measurements. The ground calibration provided data with the highest signal to noise but, because of gravity-induced distortions of the optics, could not completely characterize their performance. We present the results of on-orbit calibrations of the optics´ performance, focusing on the near on-axis field of view. We present an analysis of the energy dependence of the on-orbit PSF.
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Title: Calibration Issues for X-ray Dust Halos
Authors: Randall Smith (CfA)
Presenter: Randall Smith
Presentation Type: Oral
Abstract: Dust scattering creates diffuse X-ray halos around moderately to heavily absorbed X-ray sources. Accurately measuring the radial profile and energy dependence of these halos is crucial to constraining models of large dust grains. I will discuss a few of the calibration issues involved in this analysis. These include: (1) measuring Chandra´s PSF between 10"-1000" for both on- and off-axis pointing, (2) determining the spectrum of highly piled-up sources, and (3) using grade ratios to measure pileup.
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Title: Calibrating the Wings of the Chandra PSF
Authors: Terry Gaetz (CXC/SAO), Richard Edgar (CXC/SAO), Diab Jerius (CXC/SAO), Ping Zhao (CXC/SAO), Randall Smith (CfA)
Presenter: Terry Gaetz
Presentation Type: Oral
b>Abstract: We describe the current state of the calibration of the Chandra PSF wings. The results of a deep observation of the X-ray source Her X-1 are incorporated. The galactic Hydrogen column density (N_H) to Her X-1 is small, reducing the amplitude of any astrophysical dust scattering halo which would contaminate the mirror scattering wings. The extreme brightness of the source allows the energy dependence of the PSF wings to be probed with good statistics. The deep observation (heavily piled up in the core) is combined with a zero order gratings observation (unpiled in the core) to construct an energy-dependent profile for the PSF and wings.
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Title: Amplifier Mis-match as a Possible Source of HRC Event Position Distortions
Authors: Michael Juda (CXC)
Presenter: Michael Juda
Presentation Type: Oral
Abstract: HRC event positions are determined during processing on the ground by combining the telemetered signals from the cross-grid charge detector (CGCD) using a three-tap position algorithm. One fundamental assumption that is used in this algorithm is that the gains and offsets on the amplifier strings from the CGCD to the final output are essentially identical. An examination of on-orbit data from point sources suggests that the amplifier strings are not matched as well as expected. A large enough mis-match in the amplifier gains or offsets will lead directly to distortions in the calculated event positions, an additional detector induced blur. The HRC event processing tool, hrc_process_events, has provisions for correcting the CGCD signals for gain and offset differences. I will show comparisons of HRC data to simulations of the CGCD output with various amplifier gain and offset mis-matches. Such comparisons may guide us in the development of the calibration products to correct the CGCD signals for mis-matched amplifiers.
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Title: Where is the Source? Continuing Efforts to Improve Astrometric Accuracy
Authors: Tom Aldcroft (SAO/CXC
Presenter: Tom Aldcroft
Presentation Type: Oral
Abstract: Celestial location accuracy measures the absolute accuracy of Chandra X-ray source locations. I have recently analyzed observations of 225 point sources detected within 2 arcmin of the boresight and having accurately known coordinates. Using the existing aspect calibration data, the 90% source location error circle has a radius of 0.64 arcsec. Fewer than 1% of sources are outside a 1 arcsec radius. The majority of the outliers are in ACIS-S observations taken at off-nominal SIM-Z positions. This is understood to be a consequence of imperfections in the corner cube used to image the fiducial lights into the ACA. As the SIM is translated the fid light beam traverses different faces of the cube, inducing shifts of up to several arcsec. Using an updated calibration to account for this effect, the 90% source location error circle drops to 0.4 arcsec, and fewer than 1% of sources lie outside 0.7 arcsec.
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Title: A Parametrization of the Chandra Point Spread Function
Authors: Christopher Allen (SAO), Diab Jerius (SAO), Terry Gaetz (SAO)
Presenter: Christopher Allen
Presentation Type: Oral
Abstract: The Chandra X-ray Observatory point spread function (PSF) is a complex function of source position and energy. On-orbit calibration observations with sufficient S/N sample only a small fraction of the possible parameter space, and are complicated by detector systematics. Thus, the standard method of analyzing Chandra data uses the standard Chandra optics model as a reference. The optics model accurately simulates the telescope´s PSF, but as it is a raytrace based technique, it can be time-consuming to run and is not always appropriate for a given analysis task. A simple parameterization of the PSF would be useful for many analysis purposes, in many cases obviating the need for users to run lengthy raytraces. We present an approach to a simple PSF parameterization of off-axis point sources, discussing its applicability to analysis of Chandra observations in light of the complicated PSF structure. We also present some results of our PSF parameterization and discuss its accuracy.
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Title: Time Dependence of the ACIS Contamination
Authors: Catherine Grant (MIT CSR)
Presenter: Catherine Grant
Presentation Type: Oral
Abstract: The ACIS instrument has been accumulating a contaminant since soon after launch. ACIS-LETG measurements have been used to determine the energy-dependent absorption, but only sample a handful of times over the lifetime of the mission. Measurements of the ACIS external calibration source are taken twice every orbit in order to monitor radiation damage and are well suited to monitoring the contaminant deposition as well. I will describe how calibration source measurements can be used to measure the contaminant transmission, report on the time dependence, and compare this to other models.
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Title: Spatial Distribution of the Contaminant on the ACIS Camera
Authors: Norbert Schulz (MIT) , on behalf of the CXC ACIS Team
Presenter: Norbert Schulz
Presentation Type: Oral
Abstract: The efficiency of the ACIS instrument in the energy range below 2 keV is subject to increased levels of contamination. From studies with the external calibration source using the Mg L and Al K with the Mn K line as a reference we are able to not only monitor the change of contamination levels with time but also its spatial distribution and its change with time. We shortly review these measurements, the impact on observations, and upcoming calibration products.
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Title: Composition of the Chandra ACIS Contaminant
Authors: Herman Marshall (MIT CSR), Allyn Tennant (NASA/GSFC), Catherine Grant (MIT CSR), Adam Hitchcock (McMaster University), Steve O´Dell (NASA MSFC), Paul Plucinsky (SAO)
Presenter: Herman Marshall
Presentation Type: Oral
Abstract: The Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory is suffering a gradual loss of low energy sensitivity due to a buildup of a contaminant. High resolution spectra of bright astrophysical sources using the Chandra Low Energy Transmission Grating Spectrometer (LETGS) have been analyzed in order to determine the nature of the contaminant by measuring the absorption edges. The dominant element in the contaminant is carbon. Edges due to oxygen and fluorine are also detectable. Excluding H, we find that C, O, and F comprise >80%, 7%, and 7% of the contaminant by number, respectively. Nitrogen is less than 3% of the contaminant. We will assess various candidates for the contaminating material and investigate the growth of the layer with time. For example, the detailed structure of the C-K absorption edge provides information about the bonding structure of the compound, eliminating aromatic hydrocarbons as the contaminating material.
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Title: ACIS-S Contamination and Modeling of the X-ray Absorption in High Redshift Quasars
Authors: Aneta Siemiginowska (CFA/SAO/CXC)
Presenter: Aneta Siemiginowska
Presentation Type: Oral
Abstract: X-ray absorption in quasars provides important constraints on metalicity of the absorbers at different redshifts. Calibration at low energies and understanding effects of the contamination in Chandra ACIS-S observations are critical to these studies. I present the analysis of the Chandra ACIS-S archival data of a sample of high redshift quasars where I applied the two currently available models to compensate for the contamination effects. I focus on the uncertainties in the detected absorption based on the two methods and discuss the results.
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Title: Calibration Plan for ACIS Bake-Out
Authors: Laurence David (SAO)
Presenter: Laurence David
Presentation Type: Oral
Abstract: I will present the calibration plan for the ACIS bake-out presently scheduled for Dec. 2004. The plan is comprised of long exposures of the ACIS external calibration source to map the spatial distribution of the contaminate, gratings observations of PKS2155-304 to map the optical depth at the O-K edge, and raster scans of the supernova remnant E0102-72 to measure gain changes induced by increased CTI. The total time for this phase, including the 2 day bake-out process, is approximately 2 weeks.
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Title: Prospects for an ACIS Bakeout
Authors: Paul Plucinsky (SAO/CXC) on behalf of the MIT, NGST, PSU, MSFC & CXC teams
Presenter:Paul Plucinsky SAO/CXC
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 candidate materials for the contaminant which determine the temperatures at which the materials release. 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: Chandra X-ray Observatory Mirror Effective Area
Authors: Ping Zhao (CXC/SAO/CFA), Diab Jerius (CXC/SAO/CFA), Richard Edgar (CXC/SAO/CFA), Terrance Gaetz (CXC/SAO/CFA), Eli Beckerman (CXC/SAO/CFA), Herman Marshall (MIT)
Presenter: Ping Zhao
Presentation Type: Oral
Abstract: The HRMA Effective Area is one of the most important parameters of the Chandra X-ray Observatory. It has been calibrated to an unprecedented precision for any X-ray telescope, to ensure an accurate measurement of the flux from X-ray sources. We discuss the HRMA Effective Area measurements, based on the ground calibration made at the X-Ray Calibration Facility in Marshall Space Flight Center. We present the derivations of both on-axis and off-axis effective areas, which are currently in the CALDB and used by Chandra observers.
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Title: Effective Area of the HRMA near the Ir M-V edge at 2.1 keV
Authors: Herman Marshall (MIT), Diab Jerius (SAO), Ping Zhao, Dick Edgar, Dale Graessle, Deron Pease, Terry Gaetz, Jeremy Drake Presenter: Herman Marshall
Presentation Type: Oral
Abstract: We will present evidence that there is a residual feature in the telescope effective area. HETGS and LETGS/HRC spectra of AGN independently show a 5-10% feature, appearing as an "inverse edge" at 2.08 keV, the location of the Ir M-V edge in the HRMA effective area model. Models of the HRMA effective area can account for this feature by adding a thin hydrocarbon overlayer. The thickness of this layer should be about 10-15 A to be consistent with the observations. Plans for further investigation of this feature will be presented.
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Title: ACIS Cosmic Ray Induced QE Decrement
Authors: Yousaf Butt (CXC/SAO/CfA), Bradley Spitzbart (CXC/SAO/CfA)
Presenter: Yousaf Butt
Presentation Type: Oral
Abstract: Energetic primary cosmic rays (CRs) -as well as secondary particles and photons produced in CR interactions with the spacecraft material - deposit charge in the ACIS CCDs. This reduces the effective Quantum Efficiency (QE) of the devices to celestial X-ray photon detection. The CR response of the Front-Illuminated (FI) CCDs is different from that of the Back-Illuminated (BI). We present a preliminary report on the CR induced dead area of the ACIS FI CCDs.
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Title: Absolute ACIS Quantum Efficiency
Authors: Richard Edgar (SAO), Alexey Vikhlinin (SAO), Herman Marshall (MIT), Yousaf Butt (SAO), ACIS calibration team (SAO, MIT)
Presenter: Richard Edgar
Presentation Type: Oral
Abstract: For some time it has been aparent that there are discrepancies between the quantum efficiency (QE) curves released for front-illuminated (FI) and back-illuminated (BI, notably S3) chips in ACIS. Using the ground calibration data obtained at the X-ray Calibration Facility (XRCF) at Marshall Space Flight Center, we show that for energies below about 1 keV the S3 QE has been underestimated while that of the FI chips seems to be within a few percent of the truth. We compare these results to on-orbit and other ground-based indications of a problem with the ratio of FI/BI QE. We also discuss the effect of cosmic ray blooms, which represent a grey decrement to the QE because of unusable area. This is a few percent effect on the FI chips and negligible on the BI chips.
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Title: ACIS background
Authors: Maxim Markevitch (SAO)
Presenter: Maxim Markevitch
Presentation Type: Oral
Abstract:I will review new developments in the ACIS background area, including the possibility of modeling mild background flares.
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Title: Time-dependendent Gain in ACIS
Authors: Richard Edgar (SAO), Alexey Vikhlinin (SAO), ACIS calibration team (SAO, MIT)
Presenter: Richard Edgar
Presentation Type: Oral
Abstract: We discuss the TGAIN formalism for the correction of pulse-heights in ACIS data. The major effect of passing time on the ACIS response is a decrease in the mean PHA channel for photons of a given energy. This effect can be modeled and removed from the data using the TGAIN tool available on the contributed software page. This will be an option in the CIAO tool acis_process_events in a coming release.
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Title: A new paradigm for the generation of ACIS response matrices
Authors: Richard Edgar (SAO), Alexey Vikhlinin (SAO), ACIS calibration team (SAO, MIT)
Presenter: Richard Edgar
Presentation Type: Oral
Abstract: We discuss a new technique for generating ACIS response matrices, which obviates the need for the arduous process of producing analytical fits to the ACIS response curves. The prototype tool calcrmf2 will be available soon from the contributed software page, along with calibration files for all of the ACIS chips. We also report on improvements to the ACIS response files in the calibration database: [a] Improved modeling of the S3 response near the Si edge around 1.5 keV, and [b] Column to column variations in the quantum efficiency uniformity for BI chips.
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Title: HETG observations of Sco X-1
Authors: Norbert S. Schulz (MIT), Herman Marshall (MIT), Dave Huenemoerder (MIT), Claude Canizares (MIT), Jon Miller (CfA)
Presenter: Norbert S. Schulz
Presentation Type: Oral
Abstract: We recently observed the high flux source Sco X-1 for 15 ks with the HETGS. Sco X-1 is the brightest persistent X-ray source in the sky next to our Sun. With an average pointed X-ray flux of 10 Crab the source posed a severe risk for the longterm health of the CCDs and we therefore observed the source in a specific configuration. We shortly review this configuration, its implication for the use of existing calibrated data prodcuts and its relevance to test the higher order efficiencies of the HETGS.
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Title: Chandra LETG Diffraction Efficiencies
Authors: Brad Wargelin (SAO/CXC), Pete Ratzlaff (SAO/CXC), Deron Pease (SAO/CXC), Vinay Kashyap (SAO/CXC), Jeremy Drake (SAO/CXC)
Presenter: Brad Wargelin
Presentation Type: Oral
Abstract: Accurate calibration of the Chandra Low Energy Transmission Grating (LETG) diffraction efficiencies for all orders 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. We present results on orders 0 through 7 from analyses of on-orbit LETG/ACIS-S and LETG/HRC-S data, as well as from a reanalysis of pre-flight ground calibration data.
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Title: Degap Corrections for HRC-S Grating Observations
Authors: Vinay Kashyap (CXC/SAO), Jeremy Drake (CXC/SAO), Sun Mi Chung (CXC/SAO)
Presenter: Vinay Kashyap
Presentation Type: Oral
Abstract: We have derived empirical degap corrections for HRC-S taps over the part of the detector that covers the dispersed spectra using in-flight data. We generally use featureless continuum sources such as PKS2155-304 and HZ43 to derive a degap map and compare it with the degap coefficients derived from lab data. We find significant differences between the two, typically of the order of a few pixels, which is comparable to the line width in the HRC-S/LETG. We apply the newly derived degap map to data from line sources such as Capella and comment on its effect on the non-linearities seen in the LETGS dispersion relation.
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Title: The Dispersion Relation of the LETGS and the Accuracy of Chandra Velocity Studies
Authors: Jeremy Drake (SAO), Sun Mi Chung (SAO), Vinay Kashyap (SAO), Deron Pease (SAO), Peter Ratzlaff (SAO), Bradford Wargelin (SAO)
Presenter: Jeremy Drake
Presentation Type: Oral
Abstract: Improvements in knowledge and understanding of the Chandra LETGS wavelength calibration will be summarised and discussed. We highlight the non-linearities in the dispersion relation, and describe how we now achieve an RMS deviation of predicted vs observed line positions of 0.013 AA. We show how empirical degap maps derived from in-flight observations of bright continuum sources might lead to significant improvements. Using the example of HETG observations of the calibration source Capella and active binary Algol, we demonstrate how the Chandra gratings can be used to measure velocities to an accuracy of 20km/s and possibly better.
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Title: Status of the XMM-Newton Calibration
Authors: Marcus G.F. Kirsch (ESA), Andy M.T. Pollock (ESA), Bing Chen (ESA), Michael J.S. Smith (ESA), Maria M. Sierra (ESA), Leo Metcalfe (ESA), Bruno Altieri (ESA)
Presenter: Marcus G.F. Kirsch
Presentation Type: Oral
Abstract: The XMM-Newton observatory has been operating successfully in space since December 1999. During that time, routinely performed calibration observations, and non-routine calibration observations for special calibration topics, secured a steadily improving calibration of the observatory. In 2003 a systematic cross-calibration campaign for all the X-ray instruments was started, using all suitable existing data. We report on the current status of the XMM-Newton calibration of the individual instruments and give a status report of the cross-calibration campaign by showing results of cross-calibration for various objects.
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Title: Are Simultaneous Observations by XMM-Newton and Chandra a Luxury or a Necessity?
Authors: Andy Pollock on behalf of the XMM
Presenter: Andy Pollock
Presentation Type: Oral
Abstract: It is unusual to have two great observatories in operation at the same time with such similar but complementary capabilities. Simultaneous observations are the clearest opportunity to exploit those capabilities for both calibration and astronomical purposes. The outcome of the observations of this type made so far is reviewed here.
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Title: Overview of Chandra Calibration
Authors: Laurence David (SAO)
Presenter: Laurence David
Presentation Type: Oral
Abstract: The calibration group has been preparing a web-based document that summarizes the present Chandra calibration uncertainties. I will present The calibration group has been preparing a web-based document that summarizes the present Chandra calibration uncertainties. I will present a draft of this document and a comparison between the present calibration uncertainties and the pre-flight requirements. At present, all geometrical factors, e.g., absolute and relative Astrometry, and gratings dispersion relations are calibrated to within the requirements. The imaging properties of the HRMA are also calibrated to within the pre-flight requirements. The greatest uncertainties at present pertain to the QE of the detectors, were discrepancies of 10% still exist.
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Title: ACIS CC Mode Observations: New Bias and Split Threshold Parameters and Comparisons to TE data
Authors: Nancy Adams-Wolk (SAO), Paul Plucinsky (SAO)
Presenter: Nancy Adams-Wolk
Presentation Type: Poster
Abstract: We present the results of recent CC bias parameter and split threshold changes and the comparisons to TE mode data. We report the changes within the bias maps with the tested bias algorithms. The CC observations are compared with CTI corrected TE observations to determine how TE calibrations can be used for CC data.
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Title: Measurement of Telescope Vignetting w/ SNR G21.5-0.9
Authors: Eli Beckerman (SAO/CXC), Beth Biller (SAO/CXC), Diab Jerius (SAO/CXC)
Presenter Eli Beckerman
Presentation Type: Oral
Abstract: We present measurements of the Chandra vignetting function -- the fractional decrease in telescope throughput for off-axis objects -- using a sequence of off-axis Chandra observations of the supernova remnant G21.5-0.9. The observations were performed in such a way as to minimize the effects of detector quantum efficiency variations. We compare the results of this SNR with the current models of the vignetting function, which were used to generate the vignetting tables provided in the CALDB.
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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), Bradford Wargelin (CfA)
Presenter: Sun Mi Chung
Presentation Type: Poster
Abstract: The dispersion relation for the Chandra Low Energy Transmission Grating Spectrometer (LETGS) is known to better than 1 part in 1000 over the wavelength range of 5-150 \AA. The current dispersion relation obtained from in-flight calibration data show a significant discontinuity between the central and outer microchannel plate segments of the HRC-S imaging detector. A recent resolution of a data processing software bug that lead to a systematic error in the computation of photon wavelengths has allowed us to trace this discontinuity to the boundaries between the different plate segments of the HRC-S detector. In addition to the discontinuity of observed wavelengths between the central and outer plates, in-flight calibration data have always shown non-linear deviations in the positions of some spectral lines by as much as 0.05~\AA, which is of the order of a full width half maximum (FWHM) of a line profile. We believe these latter effects are caused by spatial non-linearities in the imaging characteristics of the HRC-S detector. Here, we present an improved dispersion relation for the LETG+HRC-S and new methods to help characterize the spatial non-linearities. We also describe an empirical approach that might be used to help improve the position determination of photon events.
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Title: Clock Correlation Contribution to Chandra Timing Accuracy
Authors: William Davis (Computer Sciences Corporation), Jeffrey Holmes (Northrop Grumman Corporation), Richard Myers (Northrop Grumman Corporation)
Presenter: William Davis
Presentation Type: Poster
Abstract: The clock correlation process synchronizes Chandra on-board timing events with a ground-based time. Specifically, coefficients are computed which provide the UTC time of the start of each minor frame. A signal synchronized to the the first of every 8 minor frames is sent to the science instruments to provide the time reference for the observed X-ray events. The clock correlation process is done entirely on the ground through time stamping of frames by the DSN network as the frames are received in real-time and through computations and curve fits by the OCC which compensate for delays on the ground and on the spacecraft as well as light travel time. This presentation summarizes the clock correlation process and its contribution to the accuracy of the timing of the observed X-ray events.
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Title: Verifying the ACIS Contamination Model with 1E0102.2-7219
Authors: Joseph DePasquale (Harvard-Smithsonian), Paul Plucinsky (Harvard-Smithsonian), Alexey Vikhlinin (Harvard-Smithsonian), Herman Marshall (MIT Center for Space), Norbert Schulz (MIT Center for Space), Richard Edgar (Harvard-Smithsonian)
Presenter: Joseph DePasquale
Presentation Type: Poster
Abstract: The low-energy sensitivity of the ACIS instrument has been continuously degrading over the last 4 years due to the accumulation of a layer of contamination on the ACIS filter and/or CCDs. This contamination layer, the result of outgassing within the telescope,introduces a new, energy dependent absorption into the ACIS response. The thickness of this layer has been increasing with time and its spatial distribution accross the ACIS focal plane has been continually changing with time. We utilize multiple observations of the SMC Supernova Remnant 1E0102.2-7219 to verify the models for the spectral, temporal and spatial dependence of the contamination layer. 1E0102.2-7219 has a soft, line-dominated spectrum which is very sensitive to the additional absorption of the contamination layer. The extensive calibration observations of 1E0102.2-7219 over the course of the mission at several different locations on the ACIS I and S arrays make this source an ideal laboratory for verifying the temporal and spatial dependence of the contamination model.
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Title: On the uncertainties in line spread function of HETG
Authors: Kazunori Ishibashi (MIT/CSR), David Huenemoerder (MIT/CSR)
Presenter: Kazunori Ishibashi
Presentation Type: Poster
Abstract: Upon analysis of spectral line profiles, it is critical to have accurate representation of line spread function (LSF) as a fitting kernel. In this presentation we discuss on the accuracy in deriving emission (or absorption) spectral line widths with using the currently available LSF models.
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Title: Gain Evolution in the HRC-S: Implications for Spectroscopy and Imaging
Authors: Deron Pease (CXC/SAO), Jeremy Drake, Jennifer Posson-Brown, Charles Wilton, R. Hank Donnelly
Presenter: Deron Pease
Presentation Type: Poster
Abstract: We present LETG/HRC-S observations of HZ 43 and PKS 2155-304 to monitor the gain evolution in the HRC-S along the LETG line of dispersion. Additionally, we present HRC-S imaging observations of AR Lac to spot-check the gain evolution spatially on the central MCP. Our analysis shows that since in-flight calibration began the median PHA has dropped by 23-28% at the nominal aimpoint, by an average of 12% along the LETG dispersion line on the central MCP, and by an average of 19% along the dispersion line on the wing MCPs. The bulk of the drop occurred within the first months of the mission, with a subsequently smaller median PHA drop of less than 10%. Current simple rate-of-decay models predict that a 5% loss of source events due to PHA drop alone is not expected for at least 10 years from October 2003.
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Title: Gain Evolution in the HRC-I
Authors: Jennifer Posson-Brown (CXC/SAO), R. Hank Donnelly (CXC/SAO)
Presenter: Jennifer Posson-Brown
Presentation Type: Poster
Abstract: Since launch, calibration observations of several sources, including AR Lac, Cas A, G21.5-0.9, and HZ 43, have been taken with the HRC-I to monitor the detector´s performance. Analysis of these observations, examining the median source pulse height amplitude (PHA) as a function of time, reveals gain fatigue in the HRC-I. We find that since the voltage adjustment in October 1999, the gain at the nominal aimpoint of the detector has declined by roughly 20%. At the twenty offset positions monitored with AR Lac, we find declines in gain ranging from roughly 4-9%, decreasing with radial distance from the aimpoint. This gradual lowering of the gain has not yet affected the quantum efficiency (QE). However, if left unchecked, the gain fatigue will eventually cause events to drop below the lower level discriminator (LLD), leading to a decline in QE.
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Title: An Update to the HRC-I MCP Quantum Efficiency Model
Authors: Jennifer Posson-Brown (CXC/SAO) , R. Hank Donnelly (CXC/SAO) , Deron Pease (CXC/SAO)
Presenter: Jennifer Posson-Brown
Presentation Type: Poster
Abstract: We present an update to the HRC-I MCP quantum efficiency (QE) model based on calibration observations of the blazar PKS 2155-304 taken in November 2002. The HRC-I observation of PKS 2155-304 was taken between two HRC-S/LETG observations of the source. These HRC-S/LETG observations allowed us to model the source and predict a count rate for the HRC-I observation. We found that this predicted rate is about 7% lower than the observed rate. Therefore, we have increased the MCP QE model of the HRC-I in the energy range 0.277 - 1.0 keV where PKS 2155-304 radiates strongly and where we previously had no flight data. Outside of this energy range, the current QE model (v. 2.1) is consistent with observations of the other calibration sources - HZ 43, Cas A, and G21.5-0.9.
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Title: Characterizing the S3 Low Energy Response with the SMC SNR 1E0102-72.3
Authors: Michael Raley (SAO), Richard Edgar (SAO), Alexey Vikhlinin (SAO), Paul Plucinsky (SAO)
Presenter: Michael Raley
Presentation Type: Poster
Abstract: Calibration observations of the SMC supernova remnant 1E0102-72.3 (E0102) indicate that problems exist with the response of the S3 chip at energies below about 1 keV, and especially at the oxygen lines below 0.7 keV. To assess these problems we have created a model spectrum based on the grating observations of this target which allows detector gains for the four strong line complexes (O VII, O VIII, Ne IX, and Ne X) to vary independently. We find that the issue of determining gains at low energies is bound up with the possibility that the line widths at these energies in the released FEF files may be too large by a few percent. We attempt to set limits on the absolute gains at the 4 line complexes, and the difference between the gains at the O VII complex (c. 568 eV) and the O VIII Lyman alpha line (653.61 eV). The median gain error for all observations for both oxygen lines on nodes 0 and 1 of the S3 chip are 2.6%. At the neon lines we get 0.8%.
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Title: Astronomical Calibration of the Chandra Clock
Authors: Arnold Rots (CfA-SAO/CXC)
Presenter: Arnold Rots
Presentation Type: Poster
Abstract: We have determined the absolute timing of the Chandra clock for an observation of the Crab pulsar made at MJD 52908.9, taking into account all known effects. This determination is based on an intercomparison of the phase of the main pulse in the pulse profile between this Chandra observation and an RXTE observation made three days later (MJD 52912.1), both referenced to the same Jodrell Bank timing ephemeris, covering the interval MJD 52883 to 52913, with geocentric epoch MJD 52898.000000156 (UTC). The final result is that there are 35 us unaccounted for, with an uncertainty of approximately 10 us.
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Title: Effects of the ACIS-S contamination in the Chandra data of Ton S180
Authors: Agata Rozanska (Copernicus Astronomi), Aneta Siemiginowska (CfA, USA), Bozena Czerny (Copernicus Astronomi)
Presenter: Agata Rozanska
Presentation Type: Poster
Abstract: We present implications of the ACIS-S contamination on the analysis of the ACIS-S/LETG data. In particular we show features present in the spectrum of a Narrow Line Seyfert 1 galaxy, Ton S180 observed in December 1999. Some absorption lines in the spectrum of Ton S180 are due to the ACIS-S contaminantion. These absorption lines should show up as a common feature in all objects even those with different redshifts. To identify the contaminantion lines we compare the data of Ton S180 to the featureless spectrum of a quasar, 3c273, observed two weeks later with the same configuration as Ton S180. The same absorption features around energy 0.22 keV are present in both 3c273 with redshift 0.156 and in Ton S180 at z=0.06198. However, we can also identify some low signal absorption lines present only in Ton S180. These lines may be related to the warm absorber in this source, which has significant implications on our understanding of the nature of NLS1. Here we focus on the difficulty of the analysis of contaminated ACIS-S data.
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Title: Improving the ACIS-S3 Spectral Resolution via a Grade-Dependent Correction?
Authors: Shanil Virani (CXC/SAO), Paul Plucinsky (CXC/SAO), Diab Jerius (CXC/SAO), Dan Nguyen (CXC/SAO), Terry Gaetz (CXC/SAO)
Presenter: Shanil Virani
Presentation Type: Poster
Abstract: We have analysed data of the external calibration source to characterize the grade-dependent spectral resolution of the ACIS-S3 CCD. As part of this analysis, we have also determined the stability of the S3 gain. Preliminary results from a work-in-progress are presented. We find that the computed line peak in PI space has shifted downwards by ~ 1 PI channel @ 1.5 keV, 1.6 PI channels @ 4.5 keV, and 1.8 PI channels @ 5.9 keV over a 3.25 year time period. We find that this shift can be corrected by applying "corr_tgain". This tool is available from the CXC. Over this time period, the line sigma has changed by ~5%, 4%, and 5% at 1.5 keV, 4.5 keV, and 5.9 keV, respectively, due to CTI. This can be largely corrected by applying the Pennsylvania State University (PSU) CTI corrector. While the line peaks in the CTI corrected data are at higher PI channels, this is presumably accounted for in the PSU response matrices. We have also attempted to improve the spectral resolution of S3 by investigating the G0, G2, G3, G4, and G6 grade distributions. We find no significant change in line peak nor line sigma by such a correction when data from the entire CCD are summed. We are in the process of investigating the position dependency of this effect. Only modest improvements are expected.
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Title: Background variability in the Chandra High Resolution Camera
Authors: Charles Wilton (CXC/SAO), Michael Juda (CXC/SAO)
Presenter: Charles Wilton
Presentation Type: Poster
Abstract: The background variability of the Chandra High Resolution Camera (HRC) was studied in order to understand the relationship between the radiation environment and the scientific usefulness of data gathered by the HRC. Variability of the scalar total rate data in excess of expected Poisson noise was correlated with Chandra Radiation Model fluxes and position of the spacecraft relative to the Earth´s magnetosphere.
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