Author
Margarita Karovska
Other affiliations: Harvard University, CFA Institute, Smithsonian Institution
Bio: Margarita Karovska is an academic researcher from Smithsonian Astrophysical Observatory. The author has contributed to research in topics: Cepheid variable & Galaxy. The author has an hindex of 29, co-authored 93 publications receiving 4329 citations. Previous affiliations of Margarita Karovska include Harvard University & CFA Institute.
Papers published on a yearly basis
Papers
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TL;DR: The CIAO (Chandra Interactive Analysis of Observations) software package was first released in 1999 following the launch of the Chandra X-ray Observatory and is used by astronomers across the world to analyze Chandra data as well as data from other telescopes.
Abstract: The CIAO (Chandra Interactive Analysis of Observations) software package was first released in 1999 following the launch of the Chandra X-ray Observatory and is used by astronomers across the world to analyze Chandra data as well as data from other telescopes. From the earliest design discussions, CIAO was planned as a general-purpose scientific data analysis system optimized for X-ray astronomy, and consists mainly of command line tools (allowing easy pipelining and scripting) with a parameter-based interface layered on a flexible data manipulation I/O library. The same code is used for the standard Chandra archive pipeline, allowing users to recalibrate their data in a consistent way. We will discuss the lessons learned from the first six years of the software's evolution. Our initial approach to documentation evolved to concentrate on recipe-based "threads" which have proved very successful. A multi-dimensional abstract approach to data analysis has allowed new capabilities to be added while retaining existing interfaces. A key requirement for our community was interoperability with other data analysis systems, leading us to adopt standard file formats and an architecture which was as robust as possible to the input of foreign data files, as well as re-using a number of external libraries. We support users who are comfortable with coding themselves via a flexible user scripting paradigm, while the availability of tightly constrained pipeline programs are of benefit to less computationally-advanced users. As with other analysis systems, we have found that infrastructure maintenance and re-engineering is a necessary and significant ongoing effort and needs to be planned in to any long-lived astronomy software.
1,145 citations
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TL;DR: The Chandra Source Catalog (CSC) as mentioned in this paper is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual Xray sources, and is designed to satisfy the needs of a broad-based group of scientists.
Abstract: The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual X-ray sources, and is designed to satisfy the needs of a broad-based group of scientists, including those who may be less familiar with astronomical data analysis in the X-ray regime. The first release of the CSC includes information about 94,676 distinct X-ray sources detected in a subset of public Advanced CCD Imaging Spectrometer imaging observations from roughly the first eight years of the Chandra mission. This release of the catalog includes point and compact sources with observed spatial extents 30''. The catalog (1) provides access to the best estimates of the X-ray source properties for detected sources, with good scientific fidelity, and directly supports scientific analysis using the individual source data; (2) facilitates analysis of a wide range of statistical properties for classes of X-ray sources; and (3) provides efficient access to calibrated observational data and ancillary data products for individual X-ray sources, so that users can perform detailed further analysis using existing tools. The catalog includes real X-ray sources detected with flux estimates that are at least 3 times their estimated 1σ uncertainties in at least one energy band, while maintaining the number of spurious sources at a level of 1 false source per field for a 100 ks observation. For each detected source, the CSC provides commonly tabulated quantities, including source position, extent, multi-band fluxes, hardness ratios, and variability statistics, derived from the observations in which the source is detected. In addition to these traditional catalog elements, for each X-ray source the CSC includes an extensive set of file-based data products that can be manipulated interactively, including source images, event lists, light curves, and spectra from each observation in which a source is detected.
527 citations
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TL;DR: The Chandra Source Catalog (CSC) as mentioned in this paper is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual Xray sources, and is designed to satisfy the needs of a broad-based group of scientists.
Abstract: The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual X-ray sources, and is designed to satisfy the needs of a broad-based group of scientists, including those who may be less familiar with astronomical data analysis in the X-ray regime. The first release of the CSC includes information about 94,676 distinct X-ray sources detected in a subset of public ACIS imaging observations from roughly the first eight years of the Chandra mission. This release of the catalog includes point and compact sources with observed spatial extents <~ 30''. The catalog (1) provides access to the best estimates of the X-ray source properties for detected sources, with good scientific fidelity, and directly supports scientific analysis using the individual source data; (2) facilitates analysis of a wide range of statistical properties for classes of X-ray sources; and (3) provides efficient access to calibrated observational data and ancillary data products for individual X-ray sources, so that users can perform detailed further analysis using existing tools. The catalog includes real X-ray sources detected with flux estimates that are at least 3 times their estimated 1 sigma uncertainties in at least one energy band, while maintaining the number of spurious sources at a level of <~ 1 false source per field for a 100 ks observation. For each detected source, the CSC provides commonly tabulated quantities, including source position, extent, multi-band fluxes, hardness ratios, and variability statistics, derived from the observations in which the source is detected. In addition to these traditional catalog elements, for each X-ray source the CSC includes an extensive set of file-based data products that can be manipulated interactively.
493 citations
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TL;DR: In this paper, Chandra X-ray images with the Advanced CCD Imaging Spectrometer spectroscopy array (ACIS-S) showed a striking richness of Xray structure at a resolution comparable to that of the best ground-based visible-light observations.
Abstract: The Chandra X-Ray Observatory observed the Crab Nebula and pulsar during orbital calibration. Zeroth-order images with the High-Energy Transmission Grating (HETG) readout by the Advanced CCD Imaging Spectrometer spectroscopy array (ACIS-S) show a striking richness of X-ray structure at a resolution comparable to that of the best ground-based visible-light observations. The HETG-ACIS-S images reveal, for the first time, an X-ray inner ring within the X-ray torus, the suggestion of a hollow-tube structure for the torus, and X-ray knots along the inner ring and (perhaps) along the inward extension of the X-ray jet. Although complicated by instrumental effects and the brightness of the Crab Nebula, the spectrometric analysis shows systematic variations of the X-ray spectrum throughout the nebula.
384 citations
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TL;DR: Zeroth-order images with the High-Energy Transmission Grating (HETG) readout by the Advanced CCD Imaging Spectrometer spectroscopy array (ACIS-S) show a striking richness of X-ray structure at a resolution comparable to that of the best ground-based visible-light observations.
Abstract: The Chandra X-ray Observatory observed the Crab Nebula and Pulsar during orbital calibration. Zeroth-order images with the High-Energy Transmission Grating (HETG) read-out by the Advanced CCD Imaging Spectrometer spectroscopy array (ACIS-S) show a striking richness of x-ray structure, at a resolution comparable to that of the best ground-based visible-light observations. The HETG--ACIS-S images reveal, for the first time, an x-ray inner ring within the x-ray torus, the suggestion of a hollow-tube structure for the torus, and x-ray knots along the inner ring and (perhaps) along the inward extension of the x-ray jet. Although complicated by instrumental effects and the brightness of the Crab Nebula, the spectrometric analysis shows systematic variations of the x-ray spectrum throughout the Nebula.
304 citations
Cited by
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University of California, Berkeley1, Goddard Space Flight Center2, Paul Scherrer Institute3, Lawrence Berkeley National Laboratory4, Oak Ridge National Laboratory5, ETH Zurich6, Montana State University7, University of Alabama in Huntsville8, University of Glasgow9, Rice University10, Open University11
TL;DR: RHESSI as discussed by the authors is a Principal Investigator (PI) mission, where the PI is responsible for all aspects of the mission except the launch vehicle, and is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/gamma-ray continua emitted by energetic electrons, and of gamma-ray lines produced by energetic ions.
Abstract: RHESSI is the sixth in the NASA line of Small Explorer (SMEX) missions and the first managed in the Principal Investigator mode, where the PI is responsible for all aspects of the mission except the launch vehicle. RHESSI is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/gamma-ray continua emitted by energetic electrons, and of gamma-ray lines produced by energetic ions. The single instrument consists of an imager, made up of nine bi-grid rotating modulation collimators (RMCs), in front of a spectrometer with nine cryogenically-cooled germanium detectors (GeDs), one behind each RMC. It provides the first high-resolution hard X-ray imaging spectroscopy, the first high-resolution gamma-ray line spectroscopy, and the first imaging above 100 keV including the first imaging of gamma-ray lines. The spatial resolution is as fine as ~ 2.3 arc sec with a full-Sun (≳ 1°) field of view, and the spectral resolution is ~ 1–10 keV FWHM over the energy range from soft X-rays (3 keV) to gamma-rays (17 MeV). An automated shutter system allows a wide dynamic range (> 107) of flare intensities to be handled without instrument saturation. Data for every photon is stored in a solid-state memory and telemetered to the ground, thus allowing for versatile data analysis keyed to specific science objectives. The spin-stabilized (~ 15 rpm) spacecraft is Sun-pointing to within ~ 0.2° and operates autonomously. RHESSI was launched on 5 February 2002, into a nearly circular, 38° inclination, 600-km altitude orbit and began observations a week later. The mission is operated from Berkeley using a dedicated 11-m antenna for telemetry reception and command uplinks. All data and analysis software are made freely and immediately available to the scientific community.
1,991 citations
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Kyle S. Dawson1, David J. Schlegel2, Christopher P. Ahn1, Scott F. Anderson3 +181 more•Institutions (51)
TL;DR: The Baryon Oscillation Spectroscopic Survey (BOSS) as discussed by the authors was designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure.
Abstract: The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure. BOSS uses 1.5 million luminous galaxies as faint as i = 19.9 over 10,000 deg2 to measure BAO to redshifts z < 0.7. Observations of neutral hydrogen in the Lyα forest in more than 150,000 quasar spectra (g < 22) will constrain BAO over the redshift range 2.15 < z < 3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyα forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance dA to an accuracy of 1.0% at redshifts z = 0.3 and z = 0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyα forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate DA (z) and H –1(z) parameters to an accuracy of 1.9% at z ~ 2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.
1,938 citations
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1,288 citations
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TL;DR: The Chandra X-Ray Observatory (CXO) as discussed by the authors is the x-ray component of NASA's Great Observatories and was launched on 1999, July 23 by the Space Shuttle Columbia.
Abstract: The Chandra X-Ray Observatory (CXO), the x-ray component of NASA's Great Observatories, was launched on 1999, July 23 by the Space Shuttle Columbia. After satellite systems activation, the first x-rays focused by the telescope were observed on 1999, August 12. Beginning with the initial observation it was clear that the telescope had survived the launch environment and was operating as expected. Despite an initial surprise due to the discovery that the telescope was far more efficient for concentrating CCD-damaging low-energy protons than had been anticipated, the observatory is performing well and is returning superb scientific data. Together with other space observatories, most notably XMM-Newton, it is clear that we have entered a new era of discovery in high-energy astrophysics.
803 citations