arXiv subjects

John C. Houck

Publications and source records attributed to John C. Houck.

8 recordsLinked to original sources

arXiv2024

The Chandra Source Catalog Release 2 Series

The Chandra Source Catalog (CSC) is a virtual X-ray astrophysics facility that enables both detailed individual source studies and statistical studies of large samples of X-ray sources detected in ACIS and HRC-I imaging observations obtained by the Chandra X-ray Observatory. The catalog provides carefully-curated, high-quality, and uniformly calibrated and analyzed tabulated positional, spatial, photometric, spectral, and temporal source properties, as well as science-ready X-ray data products. The latter includes multiple types of source- and field-based FITS format products that can be used as a basis for further research, significantly simplifying followup analysis of scientifically meaningful source samples. We discuss in detail the algorithms used for the CSC Release 2 Series, including CSC 2.0, which includes 317,167 unique X-ray sources on the sky identified in observations released publicly through the end of 2014, and CSC 2.1, which adds Chandra data released through the end of 2021 and expands the catalog to 407,806 sources. Besides adding more recent observations, the CSC Release 2 Series includes multiple algorithmic enhancements that provide significant improvements over earlier releases. The compact source sensitivity limit for most observations is ~5 photons over most of the field of view, which is ~2x fainter than Release 1, achieved by co-adding observations and using an optimized source detection approach. A Bayesian X-ray aperture photometry code produces robust fluxes even in crowded fields and for low count sources. The current release, CSC 2.1, is tied to the Gaia-CRF3 astrometric reference frame for the best sky positions for catalog sources.

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arXiv2011

Statistical Characterization of the Chandra Source Catalog

The first release of the Chandra Source Catalog (CSC) contains ~95,000 X-ray sources in a total area of ~0.75% of the entire sky, using data from ~3,900 separate ACIS observations of a multitude of different types of X-ray sources. In order to maximize the scientific benefit of such a large, heterogeneous data-set, careful characterization of the statistical properties of the catalog, i.e., completeness, sensitivity, false source rate, and accuracy of source properties, is required. Characterization efforts of other, large Chandra catalogs, such as the ChaMP Point Source Catalog (Kim et al. 2007) or the 2 Mega-second Deep Field Surveys (Alexander et al. 2003), while informative, cannot serve this purpose, since the CSC analysis procedures are significantly different and the range of allowable data is much less restrictive. We describe here the characterization process for the CSC. This process includes both a comparison of real CSC results with those of other, deeper Chandra catalogs of the same targets and extensive simulations of blank-sky and point source populations.

astro-ph.HE↗

arXiv2010

The Chandra Source Catalog

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.

astro-ph.HE↗

arXiv2006

Cosmic ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant

Supernova remnants (SNRs) are believed to be the primary location of the acceleration of Galactic cosmic rays, via diffusive shock (Fermi) acceleration. Despite considerable theoretical work the precise details are still unknown, in part because of the difficulty in directly observing nucleons that are accelerated to TeV energies in, and affect the structure of, the SNR shocks. However, for the last ten years, X-ray observatories ASCA, and more recently Chandra, XMM-Newton, and Suzaku have made it possible to image the synchrotron emission at keV energies produced by cosmic-ray electrons accelerated in the SNR shocks. In this article, we describe a spatially-resolved spectroscopic analysis of Chandra observations of the Galactic SNR Cassiopeia A to map the cutoff frequencies of electrons accelerated in the forward shock. We set upper limits on the electron diffusion coefficient and find locations where particles appear to be accelerated nearly as fast as theoretically possible (the Bohm limit).

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arXiv2006

Models for Nonthermal Photon Spectra

We describe models of nonthermal photon emission from a homogeneous distribution of relativistic electrons and protons. Contributions from the synchrotron, inverse Compton, nonthermal bremsstrahlung and neutral-pion decay processes are computed separately using a common parameterization of the underlying distribution of nonthermal particles. The models are intended for use in fitting spectra from multi-wavelength observations and are designed to be accurate and efficient. Although our applications have focused on Galactic supernova remnants, the software is modular, making it straightforward to customize for different applications. In particular, the shapes of the particle distribution functions and the shape of the seed photon spectrum used by the inverse Compton model are defined in separate modules and may be customized for specific applications. We assess the accuracy of these models by using a recurrence relation and by comparing them with analytic results and with previous numerical work by other authors.

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arXiv2003

RXTE, ROSAT and ASCA Observations of G347.3-0.5 (RX J1713.7-3946): Probing Cosmic Ray Acceleration by a Galactic Shell-Type Supernova Remnant

(Abridged) We present an analysis of the X-ray spectrum of the Galactic shell-type supernova remnant (SNR) G347.3-0.5 (RX J1713.7-3946). By performing a joint spectral analysis of data from observations made of G347.3-0.5 using the ROSAT PSPC, the ASCA GIS and the RXTE PCA, we have fit the spectra of particular regions of this SNR (including the bright northwestern and southwestern rims, the northeastern rim and the interior diffuse emission) over the approximate energy range of 0.5 through 30 keV. Based on the parameters of the best fit to the spectra using the SRCUT model, we estimate the maximum energy of cosmic-ray electrons accelerated by the rims of G347.3-0.5 to be 19-25 TeV, assuming a magnetic field strength of 10 microGauss. We present a broadband (radio to gamma-ray) photon energy flux-spectrum for the northwestern rim of the SNR, using a synchrotron-inverse Compton model with a variable magnetic field strength to fit the spectrum. Our fit derived from this model yields a maximum energy of only 8.8 TeV for the accelerated cosmic-ray electrons and a magnetic field strength of 150 microGauss. However, our derived ratio of volumes for TeV emission and X-ray emission (approximately 1000) is too large to be physically acceptable. We argue that neither non-thermal bremsstrahlung nor neutral pion decay can adequately describe the TeV emission from this rim, and therefore the physical process responsible for this emission is currently uncertain. Finally, we compare the gross properties of G347.3-0.5 with other SNRs known to possess X-ray spectra dominated by non-thermal emission.

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arXiv2002

Chandra X-Ray Spectroscopy and Imaging of the Galaxy Cluster PKS 0745-191

We present a detailed spectral and spatial analysis of the galaxy cluster PKS 0745-191, using recent observations from the Chandra X-ray Observatory. The data provide information on the temperature and metallicity of the intracluster medium, the distribution of emission throughout the cluster, morphology of the cluster core, and an independent mass estimate which can be compared to that from gravitational lensing. X-ray spectra extracted from the central 300 kpc (~2 arcmin) are well described by a two-temperature plasma and the mean cluster temperature is consistent with previously determined values. The distribution of both temperature and metallicity within the inner 360 kpc (2.3 arcmin) of PKS 0745-191 is probed on scales of 8 arcsec (~20 kpc), yielding a relatively constant abundance throughout the region and a strong temperature gradient (down to ~4-5 keV) within the central 215 kpc. Beta-model fits to the surface brightness profile of PKS 0745-191 indicate that a second beta-model component is required to fit the inner ~10 kpc. Imaging analysis of the cluster core reveals an irregular morphology within the inner 50 kpc, and confirms that the X-ray emission peak lies within 0.5 arcsec (the spatial resolution of Chandra) of both the optical and radio central cD positions. The cluster mass, based on both two temperature and multiphase fits to the X-ray spectrum, is in close agreement with lensing mass estimates of PKS-0745-191.

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arXiv1997

Recent X-Ray Observations of SN1986J with ASCA and ROSAT

We present ASCA and ROSAT observations of SN 1986J covering the period 1991 August to 1996 January. From observations with the ROSAT HRI and PSPC, we find that the 0.5-2.5 keV flux decreased proportional to $t^{-2}$ during this period; the ASCA data are consistent with this result and extend it to the 2-10 keV band. ASCA spectra from 1994 January and 1996 January are consistent with thermal emission from a solar metallicity plasma at an equilibrium temperature kT = 5-7.5 keV, somewhat hotter than that observed from other X-ray supernovae. These spectra also show a clear Fe K emission line at 6.7 keV with FWHM < 20,000 km/s (90% confidence). This limit on the line width is consistent with the reverse shock model of Chevalier & Fransson (1994), but does not rule out the clumpy wind model of Chugai (1993).

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