Timing Noise Properties of GRO J0422+32

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Abstract
OSSE observed the transient black hole candidate GRO J0422+32 (XN Persei 92) between 1992 August 11 and 1992 September 17. High time resolution data were obtained in several energy bands over the 35-600 keV range with a timing resolution of 8 ms. Power spectra at energies below 175 keV show substantial low-frequency red noise with a shoulder at a few times 10−2 Hz, peaked noise with characteristic frequency near 0.2 Hz, and a second shoulder at a few Hz. The frequencies of the shoulders and the peak are independent of energy and source intensity. The complex cross spectrum indicates that photons in the 75-175 keV band lag photons in the 35-60 keV band by a time roughly proportional to the inverse of the Fourier frequency. The maximum lag observed is 300 ms. The power and lag spectra are consistent with the production of the γ-rays through thermal Comptonization in an extended hot corona with a power-law density profile.
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