Ian N. Evans

HST imaging of the inner 3 arcseconds of NGC 1068 in the light of forbidden O III 5007 A

The Planetary Camera aboard HST has been used to obtain a high spatial resolution forbidden O III 5007 A image of the nucleus of the barred spiral galaxy NGC 1068. This image shows more detail than any previously published images and resolves the NLR into several distinct clouds arranged in an apparently conical geometry. The individual emission-line regions appear to be resolved with sizes of 0.1-0.2 arcsec. There is a strong apparent correspondence between the 1.3 cm radio structure and several of the forbidden O III 5007 A clouds, although there are also bright emission-line clouds for which there are no radio counterparts. In particular, the radio triple of Ulvestad et al. (1987) appears to correspond directly to the forbidden O III 5007 A clouds A-D. It is concluded that the distribution of the clouds is consistent with ionization core models. The hidden nucleus is located somewhere in the southern radio component and may be coincident with the H2O megamaser. 33 refs.

Hubble Space Telescope imaging of the narrow-line region of NGC 4151

We have used the Planetary Camera aboard the Hubble Space Telescope to obtain high spatial resolution [O III] λ5007 and Hα λ6563+[N II] λλ6548, 6583 images of the nucleus of NGC 4151. Almost all of the Hα λ6563+[N II] λλ6548, 6583 emission arises from an unresolved nuclear point source. The [O III] λ5007 image resolves the narrow-line region into a number of emission-line clouds distributed in a biconical structure with apices coincident with a central point source, a projected opening angle of 75°±10°, and a projected axis oriented along P.A. 60°/240°±5°. The position angle of the [O III] λ5007 emission is aligned with the extension of the nuclear VLBI radio source

A COMPLETE ATLAS OF RECALIBRATED HUBBLE SPACE TELESCOPE FAINT OBJECT SPECTROGRAPH SPECTRA OF ACTIVE GALACTIC NUCLEI AND QUASARS. I. PRE-COSTAR SPECTRA

We have recalibrated all nonpolarimetric, pre-COSTAR, archival Hubble Space Telescope Faint Object Spectrograph UV and optical spectrophotometry of active galaxies and quasars in order to extract uniformly calibrated spectrophotometric data for further detailed scientific investigations. The raw archival spectra have been recalibrated using the latest algorithms and calibration data. Spectral data contaminated by intermittent noisy diodes and cosmic-ray events have been identified manually and eliminated. Wherever possible we have combined multiple observations of the same source to produce a single spectrum per object with the highest possible signal-to-noise ratio and covering the widest wavelength range, scaling the individual data sets to the same photometric scale where necessary. Detailed quality assurance has been performed to ensure that the merged object spectra are of the highest quality consistent with the limitations of the individual data sets and calibrations. The recalibrated, merged object spectra are available in electronic form. We use this data set to present statistics of the photometric accuracy in the wavelength overlap regions for observations spanning multiple gratings.

Hubble Space Telescope observations of planetary nebulae in the Magellanic Clouds. I: The extreme type I SMP 83/WS 35

We have obtained Hubble Space Telescope Planetary Camera images in both the Hα and the [O III] λ5007 emission lines of the planetary nebula SMP 83 alias WS35, alias N66 in the Large Magellanic Cloud. By combining these results with optical and UV spectrophotometry, absolute flux measurements, and dynamical and density information, we have been able to construct a fully self-consistent nebular model. This proves that SMP 83 is an extremely massive type I object having a central star having an effective temperature of 170,000 K and a luminosity of nearly 3×10 4 L ○. . The core mass is estimated in the range 1.0-1.2 M ○. , for which the main-sequence mass was greater than ∼6 M ○. . The nebular abundances are higher than the average for the LMC and show evidence for hot-bottom burning

The optical jet in Markarian 463

Hubble Space Telescope images of Markarian 463, an interacting Seyfert 2 galaxy, reveal an optical jet 0.84 arcsec long at position angle PA≃182° originating at the Seyfert nucleus. The jet terminates at a radio point source 1.2 arcsec from the nucleus. Previous polarization observations and our filter photometry suggests that the jet may be the reflection of the hidden Seyfert 1 nucleus previously found in this galaxy

The Chandra X-ray Observatory calibration database (CalDB): building, planning, and improving

The calibration database implemented for the Chandra X-ray Observatory is the most detailed and extensive CalDB of its kind to date. Built according to the NASA High Energy Astrophysics Science Archive Research Center (HEASARC) CalDB prescription, the Chandra CalDB provides indexed, selectable calibration data for detector responses, mirror effective areas, grating efficiencies, instrument geometries, default source aim points, CCD characteristics, and quantum efficiencies, among many others. The combined index comprises approximately 500 entries. A standard FTOOLS parametric interface allows users and tools to access the index. Unique dataset selection requires certain input calibration parameters such as mission, instrument, detector, UTC date and time, and certain ranged parameter values. The goals of the HEASARC CalDB design are (1) to separate software upgrades from calibration upgrades, (2) to allow multi-mission use of analysis software (for missions with a compliant CalDB) and (3) to facilitate the use of multiple software packages for the same data. While we have been able to meet the multivariate needs of Chandra with the current CalDB implementation from HEASARC, certain requirements and desirable enhancements have been identified that raise the prospect of a developmental rewrite of the CalDB system. The explicit goal is to meet Chandras specific needs better, but such upgrades may also provide significant advantages to CalDB planning for future missions. In particular we believe we will introduce important features aiding in the development of mission-independent analysis software. We report our current plans and progress.

Chandra X-Ray Observations of the Inner Optical Filaments in Centaurus A

We have obtained Chandra High Resolution Camera (0.1-10 keV) X-ray imaging of the inner optical filaments of Cen A. Faint X-ray emission is observed associated with the filaments with significance levels of 2-3.5 σ when the data are adaptively smoothed. Comparison with optical [O III] λ5007 emission-line imaging suggests that the X-ray-emitting gas is associated with the northwest edge of the optical line-emitting gas. This region of the filaments is closest to the radio jet and is therefore a candidate for shock heating induced by turbulent instabilities in the interstellar medium. The observed X-ray luminosity is significantly smaller than that predicted by purely radiative shock models of the filaments, implying that mechanical energy input does not provide 100% of the ionizing energy budget for the filaments.

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 ~3900 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 or the 2 Mega-second Deep Field Surveys, 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.

The Chandra X-ray Observatory data processing system

Raw data from the Chandra X-ray Observatory are processed by a set of standard data processing pipelines to create scientifically useful data products appropriate for further analysis by end users. Fully automated pipelines read the dumped raw telemetry byte stream from the spacecraft and perform the common reductions and calibrations necessary to remove spacecraft and instrumental signatures and convert the data into physically meaningful quantities that can be further analyzed by observers. The resulting data products are subject to automated validation to ensure correct pipeline processing and verify that the spacecraft configuration and scheduling matched the observers request and any constraints. In addition, pipeline processing monitors science and engineering data for anomalous indications and trending, and triggers alerts if appropriate. Data products are ingested and stored in the Chandra Data Archive, where they are made available for downloading by users. In this paper, we describe the architecture of the data processing system, including the scientific algorithms that are applied to the data, and interfaces to other subsystems. We place particular emphasis on the impacts of design choices on system integrity and maintainability. We review areas where algorithmic improvements or changes in instrument characteristics have required significant enhancements, and the mechanisms used to effect these changes while assuring continued scientific integrity and robustness. We discuss major enhancements to the data processing system that are currently being developed to automate production of the Chandra Source Catalog.

A Detailed Comparison of Hubble Space Telescope Faint Object Spectrograph and IUE Ultraviolet Spectra of Selected Seyfert Nuclei

Despite the contributions of the Hubble Space Telescope Faint Object Spectrograph (FOS) to the archive of UV observations of active galactic nuclei, the vast majority of UV reference data were obtained using the International Ultraviolet Explorer (IUE) satellite. These data remain important since they provide historical information about the intensities of the UV continua and emission lines that is needed to constrain models of the active nucleus. A detailed comparison of the FOS and IUE data is critical to understanding how the measurable quantities depend on the individual instrumental calibrations, and how any conclusions derived from modeling the observations may vary depending on the source of the UV data. Rigorous comparison of FOS and IUE spectra have so far been performed only for spectrophotometric standard star observations that are acquired accurately and have high signal-to-noise ratios. We compare typical FOS spectra that were not acquired and observed with the strict regimen that is used for standard-star observations, especially in the pre-COSTAR era. All nonproprietary UV FOS spectrophotometric archival data for the Seyfert 1 galaxies Mrk 509, NGC 3783, and NGC 5548 that have near-simultaneous (within 24 hr) IUE observations are used in the analysis. These data demonstrate that the absolute photometric calibrations of the FOS and IUE agree within ~5% in absolute flux for two of the objects. For NGC 5548, the FOS and IUE flux data disagree by ~50% in the 1200-2000 A region. In this object there may be evidence for flux nonlinearity of the IUE detector and a contribution from the host galaxy redward of 2800 A. Cross-correlation of the FOS and IUE spectra reveals no zero-point wavelength shift larger than the IUE wavelength calibration errors. Comparison of line flux measurements from both the FOS and IUE spectra show that for strong emission lines (e.g., Lyα, C IV, and Mg II) the measured intensities always agree within 15%, while for moderately strong lines (e.g., N V, Si IV/O IV, He II, and C III]) the agreement is ~30% (1 σ). Weak lines (e.g., O I, C II, N IV], O III], and N III]) may not even be detected in the IUE spectra, and when they are detected the disagreement between the measured fluxes can be very large.