  OSSE observed the transient black hole candidate GRO J0422+32 (XN Per 92)
between 1992 Aug 11 and 1992 Sep 17. High time resolution data were obtained in
several energy bands over the 35-600 keV range with a sampling rate of 8 ms.
Power spectra at energies below 175 keV show substantial low-frequency red
noise with a shoulder at a few tens of mHz, 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 about 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.
