We present point-source catalogs for the ?2 Ms exposure of the Chandra Deep Field North, currently the deepest X-ray observation of the universe in the 0.5?8.0 keV band. Five hundred and three (503) X-ray sources are detected over an ?448 arcmin2 area in up to seven X-ray bands. Twenty (20) of these X-ray sources lie in the central ?5.3 arcmin2 Hubble Deep Field North (13,600 sources deg-2). The on-axis sensitivity limits are ?2.5 ? 10-17 ergs cm-2 s-1 (0.5?2.0 keV) and ?1.4 ? 10-16 ergs cm-2 s-1 (2?8 keV). Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is ?03. The X-ray colors of the detected sources indicate a broad variety of source types, although absorbed AGNs (including a small number of possible Compton-thick sources) are clearly the dominant type. We also match lower significance X-ray sources to optical counterparts and provide a list of 79 optically bright (R 23) lower significance Chandra sources. The majority of these sources appear to be starburst and normal galaxies. The average backgrounds in the 0.5?2.0 keV and 2?8 keV bands are 0.056 and 0.135 counts Ms-1 pixel-1, respectively. The background count distributions are very similar to Poisson distributions. We show that this ?2 Ms exposure is approximately photon limited in all seven X-ray bands for regions close to the aim point, and we predict that exposures up to ?25 Ms (0.5?2.0 keV) and ?4 Ms (2?8 keV) should remain nearly photon limited. We demonstrate that this observation does not suffer from source confusion within ?6' of the aim point, and future observations are unlikely to be source-confusion limited within ?3' of the aim point even for source densities exceeding 100,000 deg-2. These analyses directly show that Chandra can achieve significantly higher sensitivities in an efficient, nearly photon-limited manner and be largely free of source confusion. To allow consistent comparisons, we have also produced point-source catalogs for the ?1 Ms Chandra Deep Field South (CDF-S). Three hundred and twenty-six (326) X-ray sources are included in the main Chandra catalog, and an additional 42 optically bright X-ray sources are included in a lower significance Chandra catalog. We find good agreement with the photometry of the previously published CDF-S catalogs; however, we provide significantly improved positional accuracy.

https://iopscience.iop.org/article/10.1086/376473/pdf

The Chandra Deep Field North Survey. XIII. 2 Ms Point-Source Catalogs

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.

https://iopscience.iop.org/article/10.1086/338108/pdf

An overview of the performance and scientific results from the Chandra X-ray Observatory (CXO)

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.

The chandra source catalog

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.5 deg^2 of the COSMOS field (centered at 10 ^h , +02 ^o ) with an effective exposure of ~160 ks, and an outer 0.4 deg^2 area with an effective exposure of ~80 ks. The limiting source detection depths are 1.9 × 10^(–16) erg cm^(–2) s^(–1) in the soft (0.5-2 keV) band, 7.3 × 10^(–16) erg cm^(–2) s^(–1) in the hard (2-10 keV) band, and 5.7 × 10^(–16) erg cm^(–2) s^(–1) in the full (0.5-10 keV) band. Here we describe the strategy, design, and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2 × 10^(–5) (1655 in the full, 1340 in the soft, and 1017 in the hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (±12%) exposure across the inner 0.5 deg^2 field was obtained, leading to a sharply defined lower flux limit. The widely different point-spread functions obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with subarcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper. The full catalog is described here in detail and is available online.

/pdf/the-chandra-cosmos-survey-i-overview-and-point-source-m75usq89ip.pdf

The Chandra COSMOS Survey. I. Overview and Point Source Catalog

The Chandra X-Ray Observatory, the x-ray component of NASA's Great Observatories, was launched early in the morning of 1999, July 23 by the Space Shuttle Columbia. The Shuttle launch was only the first step in placing the observatory in orbit. After release from the cargo bay, the Inertial Upper Stage performed two firings, and separated from the observatory as planned. Finally, after five firings of Chandra's own Integral Propulsion System--the last of which took place 15 days after launch--the observatory was placed in its highly elliptical orbit of approximately 140,000 km apogee and approximately 10,000 km perigee. After activation, the first x-rays focused by the telescope were observed on 1999, August 12. Beginning with these initial observations one could see that the telescope had survived the launch environment and was operating as expected. The month following the opening of the sun-shade door was spent adjusting the focus for each set of instrument configurations, determining the optical axis, calibrating the star camera, establishing the relative response functions, determining energy scales, and taking a series of `publicity' images. Each observation proved to be far more revealing than was expected. Finally, and despite an initial surprise and setback due to the discovery that the Chandra x-ray telescope was far more efficient for concentrating low-energy protons that had been anticipated, the observatory is performing well and is returning superb scientific data. Together with other space observations, most notably the recently activated XMM-Newton, it is clear that we are entering a new era of discovery in high-energy astrophysics.

Chandra X-ray Observatory (CXO): overview

The AXAF (Advanced X-ray Astrophysics Facility) high resolution mirror assembly (HRMA) now is complete and has been tested at the NASA Marshall Space Flight Center (MSFC) X-ray Calibration Facility (XRCF). The surface and alignment properties of the mirror were thoroughly measured before the x-ray test, which allowed accurate performance predictions to be performed. The preliminary analysis of the measured x-ray image distributions for all energies tested show excellent agreement with predictions made before the beginning of the test. There is a discrepancy between the measured and predicted effective areas; this typically is less than 5%, and is less than 13% for all energies measured. We present evidence that this discrepancy is due to uncertainties in the calibration of the test instrumentation, and therefore can be expected to be reduced when results from further instrument calibration tests now in progress are incorporated into the analysis. We predict that 65 - 80% (depending upon energy) of the flux from an imaged point source will be contained on a one arc second diameter aperture in flight. We expect the HRMA to more than fulfill the requirements necessary to achieve the AXAF scientific objectives.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Performance expectation versus reality

The recently launched Chandra x-ray Observatory (CXO) was designed to have the sharpest angular resolution yet of any x-ray telescope. Detailed modeling and metrology of the optics followed by extensive testing at the X-ray Calibration Facility at the Marshall p Space Flight Center in Huntsville, Alabama, indicated that the optics were performing exceedingly well, within our ability to account for distortion of the mirrors due to gravity, and the effects of finite distance and size of the x-ray generator. Thus it was only on-orbit that we expected to directly observe the specified half arcsecond performance. We present here results of the on-orbit calibration of the point spread function (PSF), comparing it with our predictions. We discuss how the PSF varies with source location in the telescope field of view, as well as with the spectral energy distribution of the source.

/pdf/orbital-measurement-and-verification-of-the-chandra-x-ray-psiibou7yx.pdf

Orbital measurement and verification of the Chandra X-ray Observatory's PSF

Fundamental needs for future x-ray telescopes: a) Sharp images => excellent angular resolution b) High throughput => large aperture areas Generation-X optics technical challenges: a) High resolution => precision mirrors & alignment b) Large apertures => lots of lightweight mirrors Innovation needed for technical readiness: a) 4 top-level error terms contribute to image size b) There are approaches to controlling those errors Innovation needed for manufacturing readiness Programmatic issues are comparably challenging

High-Resolution X-Ray Telescopes

Instrument response uncertainties are almost universally ignored in current astrophysical X-ray data analyses. Yet modern X-ray observatories, such as Chandra and XMM-Newton, frequently acquire data for which photon counting statistics are not the dominant source of error. Including allowance for performance uncertainties is, however, technically challenging in terms of both understanding and specifying the uncertainties themselves, and in employing them in data analysis. Here we describe Monte Carlo methods developed to include instrument performance uncertainties in typical model parameter estimation studies. These methods are used to estimate the limiting accuracy of Chandra for understanding typical X-ray source model parameters. The present study indicates that, for ACIS-S3 observations, the limiting accuracy is reached for ~ 104 counts.

Monte Carlo processes for including Chandra instrument response uncertainties in parameter estimation studies

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.

/pdf/parameterization-of-the-chandra-point-spread-function-13ocq9rce3.pdf

Diab Jerius

Papers

Performance expectation versus reality

Orbital measurement and verification of the Chandra X-ray Observatory's PSF

High-Resolution X-Ray Telescopes

Monte Carlo processes for including Chandra instrument response uncertainties in parameter estimation studies

Parameterization of the Chandra point spread function