Catching Up on State Transitions in Cygnus X-1 (2008)
Boeck, Moritz, Hanke, Manfred, Wilms, Joern, Grinberg, Victoria, Pottschmidt, Katja, Markoff, Sera, ...
In 2005 February we observed Cygnus X-1 over a period of 10 days quasi-continuously with the Rossi X-ray Timing Explorer and the Ryle telescope. We present the results of the spectral and timing...
Multi-Satellite Observations of Cygnus X-1 to Study the Focused Wind and Absorption Dips (2008)
Hanke, Manfred, Wilms, Joern, Boeck, Moritz, Nowak, Michael A., Schulz, Norbert S., Pottschmidt, Katja, ...
High-mass X-ray binary systems are powered by the stellar wind of their donor stars. The X-ray state of Cygnus X-1 is correlated with the properties of the wind which defines the environment of mass...
Reynolds, Christopher S., Nowak, Michael A., Markoff, Sera, Tueller, Jack, Wilms, Joern, Young, Andrew J.
[abridged] We present an X-ray study of the low-luminosity active galactic nucleus (AGN) in NGC4258 using data from Suzaku, XMM-Newton, and the Swift/BAT survey. We find that signatures of X-ray...
Suzaku Observations of Cyg X-1 (2008)
We present highlights from a series of four simultaneous Suzaku/RXTE observations of the black hole candidate Cyg X-1. We briefly summarize several key results from our decade long RXTE monitoring...
Nowak, Michael A., Juett, Adrienne, Homan, Jeroen, Yao, Yangsen, Wilms, Joern, Schulz, Norbert S., ...
We present simultaneous Chandra-HETG and RXTE observations of a moderate flux `soft state' of the black hole candidate 4U1957+11. These spectra, having a minimally discernible hard X-ray excess, are...
Hanke, Manfred, Wilms, Joern, Nowak, Michael A., Pottschmidt, Katja, Schulz, Norbert S., Lee, Julia C.
We present analyses of a 50 ks observation of the supergiant X-ray binary system Cygnus X-1/HDE 226868 taken with the Chandra High Energy Transmission Grating Spectrometer (HETGS). Cyg X-1 was in its...
Beyond XSPEC: Towards Highly Configurable Analysis (2008)
Noble, Michael S., Nowak, Michael A.
We present a quantitative comparison between software features of the defacto standard X-ray spectral analysis tool, XSPEC, and ISIS, the Interactive Spectral Interpretation System. Our emphasis is...
Limits on Hot Galactic Halo Gas from X-ray Absorption Lines (2007)
Yao, Yangsen, Nowak, Michael A., Wang, Q. Daniel, Schulz, Norbert S., Canizares, Claude R.
Although the existence of large-scale hot gaseous halos around massive disk galaxies have been theorized for a long time, there is yet very little observational evidence. We report the Chandra and...
Tracking the Orbital and Super-orbital Periods of SMC X-1 (2007)
Trowbridge, Sarah, Nowak, Michael A., Wilms, Joern
The High Mass X-ray Binary (HMXB) SMC X-1 demonstrates an orbital variation of 3.89 days and a super-orbital variation with an average length of 55 days. As we show here, however, the length of the...
Wilms, Joern, Pottschmidt, Katja, Pooley, Guy G., Markoff, Sera, Nowak, Michael A., Kreykenbohm, Ingo, ...
We report on the first detection of a quasi-simultaneous radio-X-ray flare of Cygnus X-1. The detection was made on 2005 April 16 with pointed observations by the Rossi X-ray Timing Explorer and the...
Xiang, Jingen, Lee, Julia C., Nowak, Michael A.
We present X-ray dust scattering halo results based on our 76 ks {\it Chandra} ACIS-S/HETGS observation of the LMXB dipping source 4U 1624-490. Through analysis of the halo light curves with 2-6 keV...
I review here some of the open questions regarding the geometry and emission mechanisms of galactic black hole candidates. For hard states, I concentrate on the perspective of ``disk+Compton...
Is the ``IR Coincidence'' just that? (2005)
Nowak, Michael A., Wilms, Jörn, Heinz, Sebastian, Pooley, Guy, Pottschmidt, Katja, Corbel, Stephane
Smith, Beverly J., Struck, Curtis, Nowak, Michael A.
We present Chandra X-ray images for the interacting galaxy pair NGC 7714/5. In addition to the unresolved starburst nucleus, a variable point source with L(X) ~ 10^40 erg/s was detected 1.5" (270 pc)...
X-ray and Radio Monitoring of GX 339-4 and Cyg X-1 (2004)
Previous work by Motch et al. (1985) suggested that in the low/hard state of GX339-4, the soft X-ray power-law extrapolated backward in energy agrees with the IR flux level. Corbel and Fender (2002)...
Constraining X-ray Binary Jet Models via Reflection (2004)
Markoff, Sera, Nowak, Michael A.
Although thermal disk emission is suppressed or absent in the hard state of X-ray binaries, the presence of a cold, thin disk can be inferred from signatures of reprocessing in the ~2-50 keV band....
Fast timing instrument for XEUS: Scientific expectations (2004)
Wilms, Jörn, Kendziorra, Eckhard, Martin, Michael, Barret, Didier, Nowak, Michael A., Strüder, Lothar, ...
Bright source X-ray spectroscopy with XMM-Newton: A modified EPIC-pn timing mode (2004)
Kendziorra, Eckhard, Wilms, Jörn, Haberl, Frank, Kirsch, Marcus, Martin, Michael, Nowak, Michael A.
The Future of X-ray Spectroscopy of Galactic Black Hole Binaries (2003)
There are four major X-ray satellites currently in operation, with two more shortly to follow, and several very ambitious observatories in various stages of planning. This very rich period of X-ray...
Fluorescent iron lines as a probe of astrophysical black hole systems (2002)
Reynolds, Christopher S., Nowak, Michael A.
(abridged) With most physicists and astrophysicists in agreement that black holes do indeed exist, the focus of astrophysical black hole research has shifted to the detailed properties of these...
State Transitions in Black Hole Candidates (2002)
As described in the review by Marek Abramowicz (these proceedings), accretion theory is at something of a crossroads. Many theoretical descriptions of observations have centered on the...
Nowak, Michael A., Wilms, Joern, Dove, James B.
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...
Are There Three Peaks in the Power Spectra of GX 339-4 and Cyg X-1? (2000)
Among the variability behaviour exhibited by neutron star systems are the so-called ``horizontal branch oscillations'' (HBO, with frequencies ~50 Hz), the ``lower-frequency kHz quasi-periodic...
Implications of the X-ray Variability for the Mass of MCG-6-30-15 (1999)
Nowak, Michael A., Chiang, James
The bright Seyfert 1 galaxy \mcg shows large variability on a variety of time scales. We study the $\aproxlt 3$ day time scale variability using a set of simultaneous archival observations that were...
On the enigmatic X-ray Source V1408 Aql (=4U 1957+11) (1999)
Nowak, Michael A., Wilms, Joern
Models for the characteristically soft X-ray spectrum of the compact X-ray source V1498 Aql (=4U 1957+11) have ranged from optically thick Comptonization to multicolor accretion disk models. We...
Low Luminosity States of the Black Hole Candidate GX~339--4. II. Timing Analysis (1998)
Nowak, Michael A., Wilms, Joern, Dove, James B.
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,...
Stable Oscillations of Black Hole Accretion Discs (1998)
Nowak, Michael A., Lehr, Dana E.
The study of stable accretion disc oscillations relevant to black hole candidate (BHC) systems dates back over twenty years. Prior work has focused on both unstable and (potentially) stable disc...
RXTE Observation of Cygnus X--1: III. Implications for Compton Corona and ADAF Models (1998)
Nowak, Michael A., Wilms, Joern, Vaughan, Brian A., Dove, James B., Begelman, Mitchell C.
We have recently shown that a `sphere+disk' geometry Compton corona model provides a good description of Rossi X-ray Timing Explorer (RXTE) observations of the hard/low state of Cygnus X--1....
RXTE Observation of Cygnus X-1: II. Timing Analysis (1998)
Nowak, Michael A., Vaughan, Brian A., Wilms, Joern, Dove, James B., Begelman, Mitchell C.
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...
Radiation-Driven Warping. II. Non-Isothermal Disks (1998)
Maloney, Philip R., Begelman, Mitchell C., Nowak, Michael A.
Recent work by Pringle and by Maloney, Begelman & Pringle has shown that geometrically thin, optically thick, accretion disks are unstable to warping driven by radiation torque from the central...
RXTE Observation of Cygnus X-1: Spectral Analysis (1997)
Dove, James B., Wilms, Jorn, Nowak, Michael A., Vaughan, Brian A., Begelman, Mitchell C.
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...
Vaughan, Brian A., Nowak, Michael A.
We describe how the coherence function, a Fourier frequency-dependent measure of the linear correlation between time series measured simultaneously in two energy channels, can be used in conjunction...
Cygnus X-1: A Case for a Magnetic Accretion Disk? (1996)
Nowak, Michael A., Vaughan, Brian A., Dove, James, Wilms, Joern
With the advent of RXTE, which is capable of broad spectral coverage and fast timing, as well as other instruments which are increasingly being used in multi-wavelength campaigns (via both...
Phase Lags and Coherence of X-Ray Variability in Black Hole Candidates (1995)
Nowak, Michael A., Vaughan, Brian A.
The ``low'' (hard or ``non-thermal'') state of black hole candidates is sometimes modelled via an optically thick, hot Compton cloud that obscures a softer input source such as an accretion disk. In...
Toward a Unified View of Black Hole High Energy States (1995)
We present here a review of high energy (> 1 keV) observations of seven black hole candidates, six of which have estimated masses. In this review we focus on two parameters of interest: the ratio of...
Accretion Disc Turbulence and the X-Ray Power Spectra of Black Hole High States (1994)
Nowak, Michael A., Wagoner, Robert V.
The high state of black hole candidates is characterized by a quasi- thermal emission component at $kT \sim 1$ keV. In addition, this state tends to have very low variability which indicates that it...
A Cautionary Note on Gamma Ray Burst Nearest Neighbor Statistics (1993)
In this letter we explore the suggestion of Quashnock and Lamb (1993) that nearest neighbor correlations among gamma ray burst positions indicate the possibility of burst repetitions within various...