| Active Galactic Nuclei | |
| ASCA
Observations of the Broad Line Radio Galaxy 3C445
Rita M. Sambruna, et al., November 1997 We present the first high-resolution X-ray observation of the nearby (z=0.057) Broad Line Radio Galaxy 3C445 obtained with ASCA in 0.6-10 keV. The earlier detection of the Fe K-alpha line is confirmed. |
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| ROSAT HRI observations of the Local Group galaxies IC 10, NGC 147 and NGC 185
W. N. Brandt, et al., 22 August 1997
We report on pointed X-ray observations of IC 10, NGC 147 and NGC 185 made with the ROSAT High Resolution Imager (HRI). These are three Local Group galaxies that have never been previously studied in detail in the X-ray regime. |
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X-ray absorption by ionized oxygen in ASCA spectra of the infrared quasar IRAS
13349+2438
W. N. Brandt, et al., 14 July 1997 We present evidence for X-ray absorption by ionized oxygen in ASCA spectra of the prototype infrared quasar IRAS 13349+2438. This powerful (Lbol >= 2 X 1016 erg s-1) quasar was studied in detail with ROSAT, and the combination of the X-ray data and optical/near-infrared spectropolarimetry strongly suggested the presence of a dusty ionized ("warm") absorber along the line of sight to the central X-ray source. |
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| ASCA
spectroscopy of IRAS 23060+0505: penetrating the torus of a type 2 quasar
with X-rays
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| The
extreme X-ray luminosity of the redshift 4.72 radio-loud quasar GB 1428+4217
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| ROSAT
monitoring of persistent giant and rapid variability in the narrow-line
Th. Boller, W.N. Brandt, et al., 15 April 1997 We report evidence for presistent giant and rapid X-ray variability in the radio-quiet, ultrasoft, strong Fe II, narrow-line Seyfert 1 galaxy IRAS 13224-3809. |
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| The
remarkable properties of the ultrasoft WFC AGN Zwicky 159.034
W.N. Brandt Zwicky 159.034, one of the Seyfert galaxies identified with extreme ultraviolet sources detected during the ROSAT Wide Field Camera (WFC) all-sky survey, has unusual properties. The ROSAT Position Sensitive Proportional Counter (PSPC) X-ray spectrum, obtained simultaneously with the WFC survey, shows a remarkably soft spectrum. |
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| A
comparison of the hard ASCA spectral slopes of broad and narrow-line Seyfert
1 galaxies
W.N. Brandt, et al., 13 March 1997 The soft (~0.1 - 2.0 keV) X-ray spectra of narrow-line Seyfert 1 galaxies are known to be generally steeper than those of Seyfert 1 galaxies with broader optical permitted lines. Here we use the currently available ASCA data to systematically compare the harder (~2 - 10 keV) X-ray continua of soft ROSAT narrow-line Seyfert 1s with those of Seyfert 1s with larger HB FWHM. |
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| Steep
spectrum Seyfert galaxies
K.A. Pounds, W.N. Brandt The realization that a substantial minority of Seyfert-type AGN exhibit unusually strong and steep soft X-ray spectra is reviewed, building on observations made during the ROSAT all-sky survey. |
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| A
powerful and highly variable off-nuclear X-ray source in the composite
starburst/Seyfert 2 galaxy NGC 4945
W.N. Brandt, et al., 23 June 1996 We report on the discovery of a powerful and variable off-nuclear X-ray source in the nearby spiral galaxy NGC 4945. Twho ROSAT PSPC observations show the source to brighten in 0.5 - 2.0 keV flux by a factor of ~ 9 on a time scale of 11 months or less. |
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| AXAF CCD Imaging Spectrometer | |
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Joint AXAF high-resolution mirror assembly and AXAF CCD Imaging Spectrometer
calibration at the MSFC X-ray calibration facility
John Nousek, et. al., 1998, SPIE Proceedings The flight AXAF CCD Imaging Spectrometer (ACIS) and the High-Resolution Mirror Assembly (HRMA) telescope were extensively calibrated at NASA MSFC's X-Ray Calibration Facility (XRCF). We present results based on HRMA/ACIS characteristics that were obtained in a number of tests. The goal of the calibration is to provide accurate estimates of the in-orbit performance of the ACIS/HRMA instrument and to enable translation of in-orbit measurements to absolute values of the incident x-ray flux and physical models of the source emission. |
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Optimizing the ACIS Effective Area and Energy Resolution
Chartas et al., 1998, SPIE Proceedings, 3444 We present results describing the dependence of the Effective Area and Energy Response of ACIS/HRMA as a function of grade selection, split event threshold, CCD and CCD amplifier, and off-axis angle. |
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Discarding Piled-up Events in ACIS
Presented by John Nousek at the 1998 SPIE meeting, San Diego, California The coincidence of multiple x-rays in a detection cell within one CCD frame -- an effect known as pile-up -- is a significant source of spectral contamination for bright sources observed with the AXAF CCD Imaging Spectrometer (ACIS). Investigation of algorithms for correcting contaminated spectra is underway. In cases where such algorithms fail, the observer may wish to discard events from the core of the AXAF point spread function (PSF), computing spectra using only events from the PSF wings, where pile-up effects are reduced. This work investigates the effectiveness of this technique for an isolated on-axis point source, using event lists produced by a Monte-Carlo simulation of the ACIS instrument. |
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Pileup: Analysis of XRCF Data and Comparison with Models
Rita Sambruna and George Chartas We describe a pileup analysis based on data collected at the X-ray Calibration Facility (XRCF) in Spring 1997 during phases F and H of the calibration operations. Our primary goals are to investigate possible trends of pileup with source flux and grade selection, and to compare in detail the measured pileup fraction with the current theoretical models in order to assess the general validity of the latter for predicting pileup for in-flight observations. |
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Observing With ACIS
Presented by Gordon Garmire at the 1997 HEAD meeting, Estes Park, Colorado An overview of the ACIS instrument on the AXAF satellite. |
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| ACIS
X-ray Calibration Facility Results
Presented by John Nousek at the 1997 HEAD meeting, Estes Park, Colorado The ACIS team collected nearly 40 twenty-four hour days of calibration data at the X-ray Calibration Facility (XRCF) at the Marshall Space Flight Center. We present an overview of the types of measurements made, and sample results of the calibration, with an emphasis on joint flight ACIS/HRMA measurements. We apply the results of these measurements to considerations in selecting ACIS flight observing considerations. |
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| How
to Configure ACIS for the Typical Observing Scenario
Presented by John Nousek at the 1997 HEAD meeting, Estes Park, Colorado Although ACIS is an immensely capable instrument with a large number of potentially useful configuration options for special purposes, most observers will choose from a small number of broadly useful configurations. We present several ACIS configurations selected for use in the ACIS Guaranteed Time Observations, and explain the rationale based on the astrophysical objectives. |
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| The
ACIS PSF: Calibration Data and Modeling
Presented by Leisa Townsley at the 1997 HEAD meeting, Estes Park, Colorado The AXAF CCD Imaging Spectrometer (ACIS) consists of arrays of charge-coupled devices which pixelize and sample the AXAF focal surface with a spatial resolution of 0.49 arc seconds per pixel. We describe the ACIS-sampled AXAF point spread function (PSF) via data obtained at the X-ray Calibration Facility (XRCF) at MSFC in April 1997. |
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| ACIS
Flight Filter Transmission Models
Presented by Leisa Townsley and George Chartas at the 1997 HEAD meeting, Estes Park, Colorado The AXAF CCD Imaging Spectrometer (ACIS) employs filters made of polyimide coated on both sides with aluminum to block optical and UV light, so that the CCDs see only X-radiation from astronomical targets. We characterized these filters by spectrally and spatially mapping their transmission at astrophysically and instrumentally important energies, using the National Synchrotron Light Source (NSLS) for detailed spectral scans and the University of Wisconsin Synchrotron Radiation Center (SRC) for fine spatial mapping. |
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| ACIS
Effective Area and Energy Resolution as a Function of Grade Selection,
Split Event Threshold, CCD and CCD Amplifier Selection
Presented by George Chartas at the 1997 HEAD meeting, Estes Park, Colorado The ACIS flight instrument was recently extensively calibrated at the X-ray Calibration Facility at MSFC. For the analysis of a subset of the ACIS calibration data we have employed an automated event filtering software package developed at PSU. We present results describing the dependence of the Effective Area and Energy Response of ACIS/HRMA as a function of grade selection, split event threshold, CCD and CCD amplifier, off-axis angle and region of interest on the ACIS focal plane. |
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| Sub-pixel
Spatial Resolution Using Backside-illuminated X-ray CCDs
Leisa Townsley The FWHM of the PSF for AXAF's High Resolution Mirror Assembly is expected to be roughly 0.5 arcsec, the same size as a pixel in the AXAF CCD Imaging Spectrometer (ACIS). In order to reconstruct the PSF and obtain source positions accurate to less than 0.5 arcsec, we would like to locate individual photon interaction sites on a subpixel scale. |
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| Cosmic X-ray Background | |
| CCD Sounding
Rocket Observations of the Soft X-ray Background
Mendenhall, Burrows, et. al., 1996 Results of the first CCD observations of the X-ray background between 0.2 and 10.0 keV are presented. |
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| CUBIC | |
| CUBIC:
Preflight Calibration Results and Initial Operations
Burrows, et. al., 1996 The CUBIC instrument is designed to do moderate resolution non-dispersive X-ray spectroscopy of the diffuse X-ray background over the band 0.2 - 10.0 keV using state-of-the-art photon-counting CCDs. |
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| CUBIC:
X-ray CCD Spectroscopy of the Diffuse X-ray Background
Burrows, et. al., 1995 This paper gives an overview of the instrument design and CCD detectors. |
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| Supernova Remnants | |
| ASCA
Observations of the Supernova Remnant VRO42.05.01
Zhiyu Guo and David N. Burrows We present the results of our ASCA SIS and GIS observations of the supernova remnant VRO42.05.01. Our spectral fits indicate that the SNR is isothermal (~8.3X106 K), consistent with our ROSAT analysis results. |
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| ROSAT
Observations of the Orion-Eridanus Superbubble
David N. Burrows and Zhiyu Guo The Orion-Eridanus Bubble is a large nearby superbubble created by the Orion OB1 stellar association. X-ray emission from the interior of this superbubble, which has a temperature of about 1.2 million degrees, forms a prominent feature of the soft X-ray diffuse background. |
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| X-Ray
Morphology,Kinematics,and Geometry of the Orion-Eridanus Bubble
Z. Guo, et. al. We present mosaics of X-ray intensity maps and spectral fit results for selected regions of the Eridanus soft X-ray Enhancement (EXE), as well as absorbing clouds in the EXE region and geometrical properties of this X-ray emitting bubble. |
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| X-ray Binaries | |
| ASCA
observations of the iron K complex of Circinus X-1 near zero phase: spectral
evidence for partial covering
W.N. Brandt, et al., 3 November 1996 We report on ASCA energy spectra of Cir X-1 taken near it zero phase on 1994 August 4-5. The ASCA SIS detectors allow a much more detailed study of the iron K complex than has been possible before. We find that prior to a sudden upward flux transition the dominant iron K feature appears to consist of a large edge from neutral or nearly-neutral iron. |
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| Pre-main Sequence Stars | |
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X-ray, Star Formation and the Solar Nebula
Eric D. Feigelson, 1997 Imaging X-ray satellites have demonstrated that low-mass young stellar objects from protostars through the zero-age main sequence, exhibit high levels of magnetic activity and flaring. These in situ high energy processes may play important roles in star formation and the early history of our solar system. |
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Radio Emission from ROSAT Discovered Young Stars in and Around Taurus-Auriga
Lee Carkner, et al., 1997 An 8.4 GHz VLA survey of 91 recently discovered lithium-rich late-type stars from the ROSAT All-Sky Survey and pointed observations is presented. |
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X-ray emitting T Tauri stars in the L1551 cloud
Lee Carkner and Eric D. Feigelson Low mass pre-main sequence stars in the nearby Lynds 1551 star formaing cloud are studied with the ROSAT and ASCA X-ray satellites. An 8 ksec ROSAT image reveals 38 sources including 7 well-known T Tauri stars, 2 likely new weak-lined T Tauri stars, 5 potential new weak-lined T Tauri stars, one is a young B9 star, and the remaining sources are unrelated to the cloud or poorly identified. |
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Circularly polarized radio emission from an X-ray protostar
Eric D. Feigelson and Lee Carkner, 1996 IRS 5, an embedded young stellar object in the nearby Corona Australis molecular cloud, was recently detected as an X-ray source with the ASCA and ROSAT satellites. We report here the detection of circularly polarized continuum emission from IRS 5 at centimeter wavelengths. |
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An improved H-R diagram for Chamaeleon I pre-main sequence stars
Lawson, Feigelson, and Huenemoerder, 1996 A new Hertzsprung-Russel diagram for the Chamaeleon I cloud is constructed following the optical characterization of ROSAT X-ray sources discovered within or near the cloud boundary. |
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Dispersed T Tauri Stars and Galactic Star Formation
Eric D. Feigelson, 1996 Existing samples of low-mass T Tauri stars from nearby star forming regions are very deficient in stars older than 2 Myr. We argue that this arises from the dispersal of stars outside well-surveyed regions, and is not due to a burst of star formation, erroneous theoretical isochrones or survey flux limits. |
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Discovery of hard X-rays from a cluster of protostellar candidates
Koyama, Feigelson, et al., 1996 |
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| Observational Cosmology | |
| X-ray Detection of the Primary Lens Galaxy Cluster of the
Gravitational Lens System Q0957+561 G. Chartas, D. Chuss, W. Forman, C. Jones, and I. Shapiro, Sep 10, 1998 ApJ. Analysis of several recent ROSAT HRI observations of the gravitationally lensed system Q0957+561 has led to the detection at the 3 sigma level of the cluster lens containing the primary galaxy G1. X-ray estimates of the lensing cluster mass constrain the Hubble constant to lie in the range 67 < H0 < 82 km s-1 Mpc-1, for a time delay of 1.1 years. |
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| X-ray Detectors | |
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Charge Diffusion in CCD X-ray Detectors
George Pavlov and John Nousek Critical to the detection of X-rays by CCDs, is the detailed process of charge diffusion and drift within the device. We reexamine the prescriptions currently used in the modeling of X-ray CCD detectors to provide analytic expressions for the charge distribution over the CCD pixels which are suitable for use in numerical simulations of CCD Response. Our treatment results in models which predict charge distributions which are more centrally peaked and have flatter wings than the Gaussian shapes predicted by previous work and adopted in current CCD modelling codes. |
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CCD X-ray Detectors: On-Board Data Processing
Laura J. Cawley, et. al. We present the results of a comparison of data processing algorithms to be used with space-borne X-ray CCD cameras such as those aboard ASCA, CUBIC, and AXAF. The goal is to optimize efficiency and accuracy based upon the capabilities and limitations of the on-board processors. |
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| XMM | |
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XMM Science Simulator: EPIC Mode Performance Issues
D. H. Lumb, et. al. We describe simulations of the XMM EPIC instruments which suggest the correct operating mode must be chosen to ensure that spectral analysis of the data is not compromised by "pile-up" effects. We contrast the performance with the AXAF CCD Imaging Spectrometer ... |
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