Coronal--Temporal Correlations in GX339-4: Hysteresis, Possible Reflection Changes, and Implications for ADAFs

We present spectral fits and timing analysis of Rossi X-ray Timing Explorer observations of GX339-4. These observations were carried out over a span of more than two years and encompassed both the soft/high and hard/low states. Hysteresis in the soft state/hard state transition is observed. The hard state exhibits a possible anti-correlation between coronal compactness (i.e., spectral hardness) and the covering fraction of cold, reflecting material. The correlation between `reflection fraction' and soft X-ray flux, however, appears to be more universal. Furthermore, low flux, hard state observations - taken over a decline into quiescence- show that the Fe line, independent of `reflection fraction', remains broad and at a roughly constant equivalent width, counter to expectations from ADAF models. All power spectral densities (PSD) of the hard state X-ray lightcurves are describable as the sum of just a few broad, quasi-periodic features with frequencies that roughly scale as coronal compactness to the -3/2 power. Similar to observations of Cyg X-1, time lags between soft and hard variability anti-correlate with coronal compactness. A stronger correlation is seen between the time lags and the `reflection fraction'.Comment: 29 Pages, 17 Figures, 6 Tables. Accepted for Publication in MNRAS. (Abstract Abridged

Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects: I. Properties of the Corona and the Spectrum of Escaping Radiation

We present the properties of accretion disk corona (ADC) models, where the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a non-linear Monte Carlo code to perform the calculations. As an example, we discuss models where the corona is situated above and below a cold accretion disk with a plane-parallel (slab) geometry, similar to the model of Haardt and Maraschi. By Comptonizing the soft radiation emitted by the accretion disk, the corona is responsible for producing the high-energy component of the escaping radiation. Our models include the reprocessing of radiation in the accretion disk. Here, the photons either are Compton reflected or photo-absorbed, giving rise to fluorescent line emission and thermal emission. The self-consistent coronal temperature is determined by balancing heating (due to viscous energy dissipation) with Compton cooling, determined using the fully relativistic, angle-dependent cross-sections. The total opacity is found by balancing pair productions with annihilations. We find that, for a disk temperature kT_bb \lta 200 eV, these coronae are unable to have a self-consistent temperature higher than \sim 120 keV if the total optical depth is \gta 0.2, regardless of the compactness parameter of the corona and the seed opacity. This limitation corresponds to the angle-averaged spectrum of escaping radiation having a photon index \gta 1.8 within the 5 keV - 30 keV band. Finally, all models that have reprocessing features also predict a large thermal excess at lower energies. These constraints make explaining the X-ray spectra of persistent black hole candidates with ADC models very problematic.Comment: 15 pages, Latex, 9 .eps figures, uses emulateapj.sty (included). To be published in ApJ, October 1, 1997, Vol. 48

The Autumn Celebrations of the Ritual Calendar Year in the Later-Stuart Period

This thesis discusses the patterns in the celebrations of the autumn ritual calendar of the later-Stuart period. It focuses on the annual celebrations of the Gunpowder Treason and Plot (5th of November) and the Anniversary of the Accession of Queen Elizabeth (17th of November). For comparison, the Lord Mayor\u27s Show (29th of October) is studied. The central theme of this thesis is to distinguish between the customs and traditions of the two dominant cultures of the later-Stuart period: elite and non-elite. This thesis is broken down into three chapters. The first chapter discusses the November celebrations of the later-Stuart period. It illustrates the similarities between the 5th of November and the 17th of November by examining where the celebrations took place (indoors or outdoors) and who participated in them (elite or commoners). This thesis uses and analyzes official and partisan newspapers from the 1660s to 1715. It was through the analysis of these newspapers that the celebrants and ceremony could be discovered. The second chapter examines the participants, content, and form of the October and November celebrations. It discusses who the participants where (elite or commoner, adult or youth), what specifically occurred during these celebrations (bonfires, bells, public dancing, rough music, beer barrels, pageants, balls, banquets, and fireworks), and how the celebrations were constructed (when they began, where they commenced, the route, and where they ended). A central theme to this chapter discusses the three tiered model of the social culture extant within the late-Stuart dynasty. This three tiered model is the elite sphere, the popular sphere, and the interaction between these two cultures. The third chapter examines the continuation of these three annual celebrations into the nineteenth century

The Autumn Celebrations of the Ritual Calendar Year in the Later-Stuart Period

This thesis discusses the patterns in the celebrations of the autumn ritual calendar of the later-Stuart period. It focuses on the annual celebrations of the Gunpowder Treason and Plot (5th of November) and the Anniversary of the Accession of Queen Elizabeth (17th of November). For comparison, the Lord Mayor\u27s Show (29th of October) is studied. The central theme of this thesis is to distinguish between the customs and traditions of the two dominant cultures of the later-Stuart period: elite and non-elite. This thesis is broken down into three chapters. The first chapter discusses the November celebrations of the later-Stuart period. It illustrates the similarities between the 5th of November and the 17th of November by examining where the celebrations took place (indoors or outdoors) and who participated in them (elite or commoners). This thesis uses and analyzes official and partisan newspapers from the 1660s to 1715. It was through the analysis of these newspapers that the celebrants and ceremony could be discovered. The second chapter examines the participants, content, and form of the October and November celebrations. It discusses who the participants where (elite or commoner, adult or youth), what specifically occurred during these celebrations (bonfires, bells, public dancing, rough music, beer barrels, pageants, balls, banquets, and fireworks), and how the celebrations were constructed (when they began, where they commenced, the route, and where they ended). A central theme to this chapter discusses the three tiered model of the social culture extant within the late-Stuart dynasty. This three tiered model is the elite sphere, the popular sphere, and the interaction between these two cultures. The third chapter examines the continuation of these three annual celebrations into the nineteenth century

Low Luminosity States of the Black Hole Candidate GX 339-4. I. ASCA and Simultaneous Radio/RXTE Observations

We discuss a series of observations of the black hole candidate GX 339-4 in low luminosity, spectrally hard states. We present spectral analysis of three separate archival Advanced Satellite for Cosmology and Astrophysics (ASCA) data sets and eight separate Rossi X-ray Timing Explorer (RXTE) data sets. Three of the RXTE observations were strictly simultaneous with 843 MHz and 8.3-9.1 GHz radio observations. All of these observations have (3-9 keV) flux approximately < 10^{-9} ergs s^{-1} cm^{-2}. The ASCA data show evidence for an 6.4 keV Fe line with equivalent width 40 eV, as well as evidence for a soft excess that is well-modeled by a power law plus a multicolor blackbody spectrum with peak temperature 150-200 eV. The RXTE data sets also show evidence of an Fe line with equivalent widths 20-140 eV. Reflection models show a hardening of the RXTE spectra with decreasing X-ray flux; however, these models do not exhibit evidence of a correlation between the photon index of the incident power law flux and the solid angle subtended by the reflector. `Sphere+disk' Comptonization models and Advection Dominated Accretion Flow (ADAF) models also provide reasonable descriptions of the RXTE data. The former models yield coronal temperatures in the range 20-50 keV and optical depths of \tau ~ 3. The model fits to the X-ray data, however, do not simultaneously explain the observed radio properties. The most likely source of the radio flux is synchrotron emission from an extended outflow of size greater than O(10^7 GM/c^2).Comment: 18 pages in latex emulateapj.sty. Accepted for publication in the Astrophysical Journa

RXTE Observation of Cygnus X-1: Spectral Analysis

We present the results of the analysis of the broad-band spectrum of Cygnus X-1 from 3.0 to 200 keV, using data from a 10 ksec observation by the Rossi X-ray Timing Explorer. The spectrum can be well described phenomenologically by an exponentially cut-off power law with a photon index Gamma = 1.45 +/- 0.02 (a value considerably harder than typically found), e-folding energy E_fold = 162 +/- 9 keV, plus a deviation from a power law that formally can be modeled as a thermal blackbody with temperature kT_bb = 1.2 +/1 0.2 keV. Although the 3 - 30 keV portion of the spectrum can be fit with a reflected power law with Gamma = 1.81 +/- 0.01 and covering fraction f = 0.35 +/- 0.02, the quality of the fit is significantly reduced when the HEXTE data in the 30 - 100 keV range is included, as there is no observed hardening in the power law within this energy range. As a physical description of this system, we apply the accretion disc corona models of Dove, Wilms & Begelman (1997) --- where the temperature of the corona is determined self-consistently. A spherical corona with a total optical depth tau = 1.6 +/- 0.1 and an average temperature kT_c = 87 +/- 5 keV, surrounded by an exterior cold disc, does provide a good description of the data (reduced chi-squared = 1.55). These models deviate from the data by up to 7% in the 5 - 10 keV range, and we discuss possible reasons for these discrepancies. However, considering how successfully the spherical corona reproduces the 10 - 200 keV data, such ``photon-starved'' coronal geometries seem very promising for explaining the accretion processes of Cygnus X-1.Comment: Revised version (added content). 8 pages, 6 figures, 1 table.tex file, latex, uses mn.sty. Accepted for publication in MNRA

RXTE Observation of Cygnus X-1: II. Timing Analysis

We present timing analysis for a Rossi X-ray Timing Explorer observation of Cygnus X-1 in its hard/low state. This was the first RXTE observation of Cyg X-1 taken after it transited back to this state from its soft/high state. RXTE's large effective area, superior timing capabilities, and ability to obtain long, uninterrupted observations have allowed us to obtain measurements of the power spectral density (PSD), coherence function, and Fourier time lags to a decade lower in frequency and half a decade higher in frequency than typically was achieved with previous instruments. Notable aspects of our observations include a weak 0.005 Hz feature in the PSD coincident with a coherence recovery; a `hardening' of the high-frequency PSD with increasing energy; a broad frequency range measurement of the coherence function, revealing rollovers from unity coherence at both low and high frequency; and an accurate determination of the Fourier time lags over two and a half decades in frequency. As has been noted in previous similar observations, the time delay is approximately proportional to f^(-0.7), and at a fixed Fourier frequency the time delay of the hard X-rays compared to the softest energy channel tends to increase logarithmically with energy. Curiously, the 0.01-0.2 Hz coherence between the highest and lowest energy bands is actually slightly greater than the coherence between the second highest and lowest energy bands. We carefully describe all of the analysis techniques used in this paper, and we make comparisons of the data to general theoretical expectations. In a companion paper, we make specific comparisons to a Compton corona model that we have successfully used to describe the energy spectral data from this observation.Comment: To Be Published in the Astrophysical Journal. 18 pages. Uses emulatepaj.st

Low Luminosity States of the Black Hole Candidate GX 339-4

Here we present timing analysis of a set of eight Rossi X-ray Timing Explorer (RXTE) observations of the black hole candidate GX 339-4 that were taken during its hard/low state. On long time scales, the RXTE All Sky Monitor data reveal evidence of a 240 day periodicity, comparable to timescales expected from warped, precessing accretion disks. On short timescales all observations save one show evidence of a persistent f(qpo approximately equals 0.3 Hz quasi-periodic oscillations (QPO)). The broad band (10 (exp -3) to 10 (exp2) Hz) power appears to be dominated by two independent processes that can be modeled as very broad Lorentzians with Q approximately less than - 1. The coherence function between soft and hard photon variability shows that if these are truly independent processes, then they are individually coherent, but they are incoherent with one another. This is evidenced by the fact that the coherence function between the hard and soft variability is near unity between 5 x 10 (exp -3) but shows evidence of a dip at f approximately equals 1 Hz. This is the region of overlap between the broad Lorentzian fits to the Power Spectral Density (PSD). Similar to Cyg X-1, the coherence also drops dramatically at frequencies approximately greater than 1O Hz. Also similar to Cyg X-1, the hard photon variability is seen to lag the soft photon variability with the lag time increasing with decreasing Fourier frequency. The magnitude of this time lag appears to be positively correlated with the flux of GX 339-4. We discuss all of these observations in light of current theoretical models of both black hole spectra and temporal variability