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Discovery of Microsecond Time Lags in Kilohertz QPOs

Vaughan, B. A. and van der Klis, M. and Méndez, M. and van Paradijs, J. and Wijnands, R. A. D. and Lewin, W. H. G. and Lamb, F. K. and Psaltis, D. and Kuulkers, E. and Oosterbroek, T. (1997) Discovery of Microsecond Time Lags in Kilohertz QPOs. Astrophysical Journal Letters, 483 (2). L115-L118. ISSN 2041-8205.

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Using the Rossi X-Ray Timing Explorer, we have measured ~27 μs time delays in 830 Hz quasi-periodic oscillations (QPOs) between 4-6 and 11-17 keV in 4U 1608-52, with high-energy photons lagging low-energy photons, and found upper limits to the time delays of 45 μs between 2-6.5 and 6.5-67 keV in ~730 Hz QPOs in 4U 0614+091 and 30 μs between 8.7-12.4 and 12.4-67 keV in ~870 Hz QPOs in 4U 1636-53. We also find that the cross-coherence function between QPOs at different energies is greater than 0.85 with 95% confidence in 4U 1608-52 and 4U 1636-53. If Compton upscattering of low-energy X-rays in a region with an optical depth of a few is responsible for the delays, then the Compton upscattering region is between a few kilometers and a few tens of kilometers in size.

Item Type:Article
Related URLs:
URLURL TypeDescription
van der Klis, M.0000-0003-0070-9872
Lamb, F. K.0000-0002-3862-7402
Additional Information:© 1997. American Astronomical Society. Received 1997 January 3, accepted for publication 1997 April 22. An Erratum for this article has been published in 1998 ApJ 509 L145. The authors acknowledge Michael Nowak and Lev Titarchuk for useful comments and suggestions. B. A. V. acknowledges support from the United States National Aeronautics and Space Administration (NASA) under grants NAG 5-3340 and NAG 5-3293. J. v. P. acknowledges support from NASA under grant NAG 5-3269. T. O. acknowledges a European Space Agency (ESA) research fellowship. F. K. L. and D. P. acknowledge NSF grants AST-9315133 and AST-9618524 and NASA grant NAG 5-2925. M. M. is a fellow of the Consejo Nacional de Investigaciones Cientı´ficas y Te´cnicas de la Repu´blica Argentina. W. H. G. L. acknowledges support from NASA. This work was supported in part by the Netherlands Organization for Scientific Research (NWO) under grant PGS 78-277 and by the Netherlands Foundation for Research in Astronomy (ASTRON) under grant 781-76-017.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
NASANAG 5-3340
NASANAG 5-3293
NASANAG 5-3269
NASANAG 5-2925
Non-Subject Keywords:accretion, accretion disks; stars: individual (4U 1608–52, 4U 0614+614, 4U 1636–53); stars: neutron; X-rays: stars
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory1997-48
Issue or Number:2
Record Number:CaltechAUTHORS:20141203-102713239
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52320
Deposited By: Deborah Miles
Deposited On:03 Dec 2014 20:56
Last Modified:09 Mar 2020 13:19

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