Imagine the Universe!

Jim's Ph.D. Research Project

In this project, Jim tried to understand what causes the X-ray variability in Cyg X-1. Because of these variations, Cyg X-1 is a very interesting source, one which has been studied by many but understood by few (if it is understood completely by anyone!).

Jim considered two possibilities: 1) the variability was caused by a chaotic process but governed by a small set of variable parameters (which could be easily modeled) and 2) the variability could be explained by a traditional shot noise model improved so that it more closely matched the observed variability.

He found that the answer to 1) was that there was too much noise in the data, which made it difficult to discern given the technique he was using. The answer to 2) was "Yes! an improved shot-noise model would work." Jim then developed an extension of the shot models. These models were better at reproducing the observations, so they gave insight into what physical processes in the Cyg X-1 system were occurring to cause the observed variability.

Cyg X-1 Longterm Cyg X-1 Shortterm
RXTE data from Cyg X-1
Short timescale RXTE data from Cyg X-1
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Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

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