Timing noise properties of GRO J0422+32

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 similar or equal to 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 similar or equal to 300 ms. The power and lag spectra are consistent with the production of the gamma-rays through thermal Comptonization in an extended hot corona with a power-law density profile.