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We present a detailed examination on the coronal nonthermal emissions duringthe preflare phase of the X4.8 flare that occurred on 2002 July 23. Themicrowave (17 GHz and 34 GHz) data obtained with Nobeyama Radioheliograph, atNobeyama Solar Radio Observatory and the hard X-ray (HXR) data taken with {\itReuven Ramaty High Energy Solar Spectroscopic Imager} obviously showednonthermal sources that are located above the flare loops during the preflarephase. We performed imaging spectroscopic analyses on the nonthermal emissionsources both in microwaves and in HXRs, and confirmed that electrons areaccelerated from several tens of keV to more than 1 MeV even in this phase. Ifwe assume the thin-target model for the HXR emission source, the derivedelectron spectral indices ($\sim 4.7$) is the same value as that frommicrowaves ($\sim 4.7$) within the observational uncertainties, which impliesthat the distribution of the accelerated electrons follows a single power-law.The number density of the microwave-emitting electrons is, however, larger thanthat of the HXR-emitting electrons, unless we assume low ambient plasma densityof about $1.0 \times 10^9$ cm$^{-3}$ for the HXR-emitting region. If we adoptthe thick-target model for the HXR emission source, on the other hand, theelectron spectral index ($\sim 6.7$) is much different, while the gap of thenumber density of the accelerated electrons is somewhat reduced.

Imaging Spectroscopy on Preflare Coronal Nonthermal Sources Associated with the 2002 July 23 Flare