A Caltech Library Service

X-Ray Variability Coherence: How to Compute It, What It Means, and How It Constrains Models of GX 339-4 and Cygnus X-1

Vaughan, Brian A. and Nowak, Michael A. (1997) X-Ray Variability Coherence: How to Compute It, What It Means, and How It Constrains Models of GX 339-4 and Cygnus X-1. Astrophysical Journal Letters, 474 (1). L43-L46. ISSN 2041-8205. doi:10.1086/310430.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


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 with energy spectra, power spectra, and time delays between energy channels to constrain models of the spectrum and variability of X-ray binaries. Here we present a procedure for estimating the coherence function in the presence of counting noise. We apply this method to the black hole candidates Cyg X-1 and GX 33924 and find that the near-perfect coherence between low- and high-energy X-ray photons rules out a wide range of models that postulate spatially extended fluctuating emission, thermal flares, and overlapping shot noise.

Item Type:Article
Related URLs:
URLURL TypeDescription
Nowak, Michael A.0000-0001-6923-1315
Additional Information:Copyright 1997. American Astronomical Society. The authors would like to acknowledge useful conversations with Peter Michelson, Michiel van der Klis, Mitch Begelman, James Dove, and John Wilms, as well as generous support from NASA grants NAG 5-3239 (B. A. V.) and NAG 5-3225 (M. A. N.) and the Netherlands Organization for Scientific Research (NWO) under grant PGS 78-277.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Non-Subject Keywords:BLACK HOLE PHYSICS, METHODS: STATISTICAL, X-RAYS: STARS, Black Hole Physics, Methods: Statistical, X-Rays: Stars
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory1997-54
Issue or Number:1
Record Number:CaltechAUTHORS:20141203-111905220
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52330
Deposited By: Deborah Miles
Deposited On:08 Dec 2014 02:49
Last Modified:10 Nov 2021 19:24

Repository Staff Only: item control page