Comptonization and the Spectra of Accretion-Powered X-Ray Pulsars

Accretion-powered X-ray pulsars are among the most luminous X-ray sources in the Galaxy. However, despite decades of theoretical and observational work since their discovery, no satisfactory model for the formation of the observed X-ray spectra has emerged. In this paper, we report on a self-consistent calculation of the spectrum emerging from a pulsar accretion column that includes an explicit treatment of the bulk and thermal Comptonization occurring in the radiation-dominated shocks that form in the accretion flows. Using a rigorous eigenfunction expansion method, we obtain a closed-form expression for the Green's function describing the upscattering of monochromatic radiation injected into the column. The Green's function is convolved with bremsstrahlung, cyclotron, and blackbody source terms to calculate the emergent photon spectrum. We show that energization of photons in the shock naturally produces an X-ray spectrum with a relatively flat continuum and a high-energy exponential cutoff. Finally, we demonstrate that our model yields good agreement with the spectra of the bright pulsar Her X-1 and the low luminosity pulsar X Per.Comment: 6 Pages, 2 Figures, To appear in "The Multicoloured Landscape of Compact Objects and their Explosive Progenitors" (Cefalu, Sicily, June 2006). Eds. L. Burderi et al. (New York: AIP

Vertical Distribution of Aersols and Water Vapor Using CRISM Limb Observations

Near-infrared spectra taken in a limb-viewing geometry by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on-board the Mars Reconnaissance Orbiter (MRO) provide a useful tool for probing atmospheric structure. Specifically, the observed radiance as a function of wavelength and height above the limb allows the vertical distribution of both dust and ice aerosols to be retrieved. These data serve as an important supplement to the aerosol profiling provided by the MRO/MCS instrument allowing independent validation and giving additional information on particle physical and scattering properties through multi-wavelength studies. A total of at least ten CRISM limb observations have been taken so far covering a full Martian year. Each set of limb observations nominally contains about four dozen scans across the limb giving pole-to-pole coverage for two orbits at roughly 100 and 290 W longitude over the Tharsis and Syrtis/Hellas regions, respectively. At each longitude, limb scans are spaced roughly 10 degrees apart in latitude, with a vertical spatial resolution on the limb of roughly 800 m. Radiative transfer modeling is used to model the observations. We compute synthetic CRISM limb spectra using a discrete-ordinates radiative transfer code that accounts for multiple scattering from aerosols and accounts for spherical geometry of the limb observations by integrating the source functions along curved paths in that coordinate system. Retrieved are 14-point vertical profiles for dust and water ice aerosols with resolution of 0.4 scale heights between one and six scale heights above the surface. After the aerosol retrieval is completed, the abundances of C02 (or surface pressure) and H20 gas are retrieved by matching the depth of absorption bands at 2000 nm for carbon dioxide and at 2600 run for water vapor. In addition to the column abundance of water vapor, limited information on its vertical structure can also be retrieved depending on the signal available from aerosol scattering

CRISM Observations of Water Vapor and Carbon Monoxide

Near-infrared spectra returned by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM, [1]) on-board the Mars Reconnaissance Orbiter (MRO) contain the clear spectral signature of several atmospheric gases including carbon dioxide (CO2), water vapor (H2O), and carbon monoxide (CO). Here we describe the seasonal and spatial mapping of water vapor and carbon dioxide for one full Martian year using CRISM spectra

Uniform Maine Citations, 2016 - 2017 Edition (superseded)

https://digitalcommons.mainelaw.maine.edu/uniform-maine-citations/1000/thumbnail.jp

Measuring Extinction Curves of Lensing Galaxies

We critique the method of constructing extinction curves of lensing galaxies using multiply imaged QSOs. If one of the two QSO images is lightly reddened or if the dust along both sightlines has the same properties then the method works well and produces an extinction curve for the lensing galaxy. These cases are likely rare and hard to confirm. However, if the dust along each sightline has different properties then the resulting curve is no longer a measurement of extinction. Instead, it is a measurement of the difference between two extinction curves. This "lens difference curve'' does contain information about the dust properties, but extracting a meaningful extinction curve is not possible without additional, currently unknown information. As a quantitative example, we show that the combination of two Cardelli, Clayton, & Mathis (CCM) type extinction curves having different values of R(V) will produce a CCM extinction curve with a value of R(V) which is dependent on the individual R(V) values and the ratio of V band extinctions. The resulting lens difference curve is not an average of the dust along the two sightlines. We find that lens difference curves with any value of R(V), even negative values, can be produced by a combination of two reddened sightlines with different CCM extinction curves with R(V) values consistent with Milky Way dust (2.1 < R(V) < 5.6). This may explain extreme values of R(V) inferred by this method in previous studies. But lens difference curves with more normal values of R(V) are just as likely to be composed of two dust extinction curves with R(V) values different than that of the lens difference curve. While it is not possible to determine the individual extinction curves making up a lens difference curve, there is information about a galaxy's dust contained in the lens difference curves.Comment: 15 pages, 4 figues, ApJ in pres

Uniform Maine Citations, 2019 - 2020 Edition (Superseded)

Uniform Maine Citations is organized so that similar types of references to Maine authorities appear together. The organization is grouped by primary or secondary research materials, including subdivisions for (1) statutory and legislative materials, including constitutions, statutes, legislative documents, and municipal ordinances; (2) court decisions, rules, and documents; (3) executive agency regulations, reports, and other documents; and (4) secondary materials that analyze and interpret the primary materials, including Maine-specific treatises, practice books, and legal periodicals. Beyond guidance for proper citation, the primary and secondary sources identified in this edition constitute a useful catalog of materials available to support research into Maine legal authority and sources that discuss them. Further, Uniform Maine Citations identifies the major law libraries and the state and federal court and state government websites that provide free access to primary sources for Maine-specific legal research materials. Maine Uniform Citations undertakes to provide annually updated guidance for the proper form for citation to and location of Maine-specific primary and secondary legal source material. As with the editions that most recently preceded it, this edition is published on the University of Maine School of Law website alongside the Maine Law Review page and is updated at least annually on the academic calendar to recognize new developments and new sources of Maine-related legal research.https://digitalcommons.mainelaw.maine.edu/uniform-maine-citations/1015/thumbnail.jp

Uniform Maine Citations, 2022-2024 Edition

Uniform Maine Citations is organized so that similar types of references to Maine authorities appear together. The organization is grouped by primary or secondary research materials, including subdivisions for (1) statutory and legislative materials, including constitutions, statutes, legislative documents, and municipal ordinances; (2) court decisions, rules, and documents; (3) executive agency regulations, reports, and other documents; and (4) secondary materials that analyze and interpret the primary materials, including Maine-specific treatises, practice books, and legal periodicals. Beyond guidance for proper citation, the primary and secondary sources identified in this edition constitute a useful catalog of materials available to support research into Maine legal authority and sources that discuss them. Further, Uniform Maine Citations identifies the major law libraries and the state and federal court and state government websites that provide free access to primary sources for Maine-specific legal research materials. Maine Uniform Citations undertakes to provide annually updated guidance for the proper form for citation to and location of Maine-specific primary and secondary legal source material. As with the editions that most recently preceded it, this edition is published on the University of Maine School of Law website alongside the Maine Law Review page and is updated at least annually on the academic calendar to recognize new developments and new sources of Maine-related legal research.https://digitalcommons.mainelaw.maine.edu/uniform-maine-citations/1018/thumbnail.jp

Uniform Maine Citations, 2020 - 2021 Edition (Superseded)

Uniform Maine Citations is organized so that similar types of references to Maine authorities appear together. The organization is grouped by primary or secondary research materials, including subdivisions for (1) statutory and legislative materials, including constitutions, statutes, legislative documents, and municipal ordinances; (2) court decisions, rules, and documents; (3) executive agency regulations, reports, and other documents; and (4) secondary materials that analyze and interpret the primary materials, including Maine-specific treatises, practice books, and legal periodicals. Beyond guidance for proper citation, the primary and secondary sources identified in this edition constitute a useful catalog of materials available to support research into Maine legal authority and sources that discuss them. Further, Uniform Maine Citations identifies the major law libraries and the state and federal court and state government websites that provide free access to primary sources for Maine-specific legal research materials. Maine Uniform Citations undertakes to provide annually updated guidance for the proper form for citation to and location of Maine-specific primary and secondary legal source material. As with the editions that most recently preceded it, this edition is published on the University of Maine School of Law website alongside the Maine Law Review page and is updated at least annually on the academic calendar to recognize new developments and new sources of Maine-related legal research.https://digitalcommons.mainelaw.maine.edu/uniform-maine-citations/1016/thumbnail.jp

Uniform Maine Citations, 2018 - 2019 Edition (Superseded)

Uniform Maine Citations is organized so that similar types of references to Maine authorities appear together. The organization is grouped by primary or secondary research materials, including subdivisions for (1) statutory and legislative materials, including constitutions, statutes, legislative documents, and municipal ordinances; (2) court decisions, rules, and documents; (3) executive agency regulations, reports, and other documents; and (4) secondary materials that analyze and interpret the primary materials, including Maine-specific treatises, practice books, and legal periodicals. Beyond guidance for proper citation, the primary and secondary sources identified in this edition constitute a useful catalog of materials available to support research into Maine legal authority and sources that discuss them. Further, Uniform Maine Citations identifies the major law libraries and the state and federal court and state government websites that provide free access to primary sources for Maine-specific legal research materials. Maine Uniform Citations undertakes to provide annually updated guidance for the proper form for citation to and location of Maine-specific primary and secondary legal source material. As with the editions that most recently preceded it, this edition is published on the University of Maine School of Law website alongside the Maine Law Review page and is updated at least annually on the academic calendar to recognize new developments and new sources of Maine-related legal research.https://digitalcommons.mainelaw.maine.edu/uniform-maine-citations/1014/thumbnail.jp