X-ray Observations of AGN at Intermediate to High Redshift

The cores of active galactic nuclei (AGN) harbor some of the most extreme conditions of matter and energy in the Universe. One of the major goals of high-energy astrophysics is to probe these extreme environments in the vicinity of supermassive black holes, which are intimately linked to the mechanisms that produce the continuum emission in AGN. X-ray studies seek to understand the physics responsible for the continuum emission, its point of origin, how nuclear activity is fueled, and how supermassive black holes evolve. The key to finding answers to these questions lies in measuring the intrinsic luminosities and spectral shapes, the relation of these properties to other wavebands, and how the source properties change with redshift. This article reviews X-ray observations of AGN from redshifts of ~0.1-3 with the goal of summarizing our current knowledge of their X-ray spectral characteristics. Results are evaluated in terms of their robustness and are examined in the light of current theoretical predictions of energy release via processes associated with the accretion mechanism. A possible evolutionary scenario is discussed, along with the importance of AGN studies at high redshift as they relate to the total energetics of the Universe.Comment: 10 pages, 1 figure. To appear in the proceedings of the 9th Annual October Maryland Astrophysics Conference, After the Dark Ages: When galaxies Were Youn

Probing Dense Matter in the cores of AGN: Observations with RXTE and ASCA

Preliminary results from an X-ray spectral study of Seyfert 1 galaxies with ASCA and RXTE are presented. From an analysis of X-ray reprocessing features of Compton reflection and Fe K-alpha fluorescence, it is found that iron line strength is not necessarily a good predictor of the amount of reflection. The variability properties of Fe K-alpha and reflection do not necessarily scale together and substantial decoupling of the behavior of the reprocessed flux with respect to continuum variability is common. Such trends suggest the presence of multiple and/or complex regions of dense matter in AGN cores and that standard accretion disk models drastically oversimplify reality.Comment: 4 pages, 2, two-panel figures, latex. To appear in "Proceedings of X-ray Astronomy '99 - Stellar Endpoints, AGN and the Diffuse Background," 2000. G. Malaguti, G. Palumbo & N. White (eds), Gordon & Breach (Singapore

Investigation of the geology, mineral resources and water resources of the state of Maryland

There are no author-identified significant results in this report

The Benefits of Peer Review and a Multisemester Capstone Writing Series on Inquiry and Analysis Skills in an Undergraduate Thesis.

This study examines the relationship between the introduction of a four-course writing-intensive capstone series and improvement in inquiry and analysis skills of biology senior undergraduates. To measure the impact of the multicourse write-to-learn and peer-review pedagogy on student performance, we used a modified Valid Assessment of Learning in Undergraduate Education rubric for Inquiry and Analysis and Written Communication to score senior research theses from 2006 to 2008 (pretreatment) and 2009 to 2013 (intervention). A Fisher-Freeman-Halton test and a two-sample Student's t test were used to evaluate individual rubric dimensions and composite rubric scores, respectively, and a randomized complete block design analysis of variance was carried out on composite scores to examine the impact of the intervention across ethnicity, legacy (e.g., first-generation status), and research laboratory. The results show an increase in student performance in rubric scoring categories most closely associated with science literacy and critical-thinking skills, in addition to gains in students' writing abilities

RXTE and BeppoSAX Observations of MCG -5-23-16: Reflection From Distant Cold Material

We examine the spectral variability of the Seyfert 1.9 galaxy MCG -5-23-16 using RXTE and BeppoSAX observations spanning 2 years from April 1996 to April 1998. During the first year the X-ray source brightens by a factor of ~25% on timescales of days to months. During this time, the reprocessed continuum emission seen with RXTE does not respond measurably to the continuum increase. However, by the end of the second year during the BeppoSAX epoch the X-ray source has faded again. This time, the reprocessed emission has also faded, indicating that the reprocessed flux has responded to the continuum. If these effects are caused by time delays due to the distance between the X-ray source and the reprocessing region, we derive a light crossing time of between ~1 light day and ~1.5 light years. This corresponds to a distance of 0.001 pc to 0.55 pc, which implies that the reprocessed emission originates between 3x10^15 cm and 1.6x10^18 cm from the X-ray source. In other words, the reprocessing in MCG -5-23-16 is not dominated by the inner regions of a standard accretion disk.Comment: Accepted for publication in ApJ. 17 pages, 8 figure

Oscillatory approach to the singularity in vacuum T2T^2 symmetric spacetimes

A combination of qualitative analysis and numerical study indicates that vacuum $T^2$ symmetric spacetimes are, generically, oscillatory.Comment: 2 pages submitted to the Ninth Marcel Grossmann Proceedings; v2, "all known cases" changed to "various known cases" in the first paragrap

X-ray Evidence for Multiple Absorbing Structures in Seyfert Galaxies

We have used X-ray spectra to measure attenuating columns in a large sample of Seyfert galaxies. Over 30 of these sources have resolved radio jets, allowing the relative orientation of the nucleus and host galaxy to be constrained. We have discovered that the distribution of absorbing columns is strongly correlated with the relative orientation of the Seyfert structures. This result is inconsistent with unification models including only a torus and is instead most readily explained if a second absorber is included: in addition to a Compton-thick, parsec-scale torus there would also be a larger-scale absorber with N_H < 10^{23} cm^{-2}. The second absorber is aligned with the host galactic plane while the torus is arbitrarily misaligned.Comment: 2 pages, 1 figure, to appear in "Multiwavelength AGN Surveys" (Cozumel, December 8-12 2003), ed. R. Maiolino and R. Mujica, Singapore: World Scientific, 2004. Additional material may be found at http://space.mit.edu/home/jonathan/research.htm

On the area of the symmetry orbits in T2T^2 symmetric spacetimes

We obtain a global existence result for the Einstein equations. We show that in the maximal Cauchy development of vacuum $T^2$ symmetric initial data with nonvanishing twist constant, except for the special case of flat Kasner initial data, the area of the $T^2$ group orbits takes on all positive values. This result shows that the areal time coordinate $R$ which covers these spacetimes runs from zero to infinity, with the singularity occurring at R=0.Comment: The appendix which appears in version 1 has a technical problem (the inequality appearing as the first stage of (52) is not necessarily true), and since the appendix is unnecessary for the proof of our results, we leave it out. version 2 -- clarifications added, version 3 -- reference correcte