HEAD Division Meeting 1999, April 1999
Session 15. X-Ray Binaries
Poster, Tuesday, April 13, 1999, 8:30am-6:02pm, Gold Room

[Previous] | [Session 15] | [Next]


[15.01] Measurement of Energy-Dependent Lags in Four Galactic Low Mass X-ray Binary Systems

C.B. Markwardt (NASA/GSFC), H.C. Lee (Northwestern Univ.), J.H. Swank (NASA/GSFC)

The measurement of energy dependent time lags in the X-ray emission from galactic low mass X-ray binaries holds the promise of constraining the emission geometry and mechanisms. This hope is especially strong for sources with kilohertz quasiperiodic oscillations (QPOs), whose mechanism is largely still a mystery. From the energy spectrum of these sources, one might infer the presence of a hot corona which should in turn inverse Compton scatter softer seed photons, leading to hard lags. Such lags are present at low frequencies (< 30 Hz). However, we find soft lags in the ``lower'' kilohertz QPO peak for the Atoll sources 4U~1608-52 (see Vaughan et al 1998 [erratum]), 4U~1636-536 (also Kaaret et al 1999), 4U~1728-34, and 4U~1702-429, with magnitudes reaching ~50 \mus. Further, we show that the lag spectrum of upper kilohertz peak in at least one of the sources is entirely inconsistent with soft lags, and indeed suggests a hard lag. This fact alone strongly implies that either the emission mechanisms for the oscillations are distinct, or the emission regions are distinct.


If the author provided an email address or URL for general inquiries, it is as follows:

craigm@lheamail.gsfc.nasa.gov


[Previous] | [Session 15] | [Next]