AN INTENSE GAMMA-RAY FLARE OF PKS-1622-297

We report the observation by the Compton Gamma Ray Observatory of a sp ectacular flare of radio source PKS 1622-297. A peak flux of (17 +/- 3 ) x 10(-6) cm(-2) s(-1) (E > 100 MeV) was observed. The corresponding isotropic luminosity is 2.9 x 10(49) ergs s(-1). We find that PKS 1622 -297 exhibits gamma-ray intraday variability. A flux increase by a fac tor of at least 3.6 was observed to occur in less than 7.1 hr (with 99 % confidence). Assuming an exponential rise, the corresponding doublin g time is less than 3.8 hr. A significant flux decrease by a factor of similar to 2 in 9.7 hr was also observed. Without beaming, the rapid flux change and large isotropic luminosity are inconsistent with the E lliot-Shapiro condition (assuming that gas accretion is the immediate source of power for the gamma-rays). This inconsistency suggests that the gamma-ray emission is beamed. A minimum Doppler factor of 8.1 is i mplied by the observed lack of pair-production opacity (assuming X-ray s are emitted cospatially with the gamma-rays). Simultaneous observati on by EGRET and OSSE finds a spectrum adequately fitted by a power law with photon index of -1.9. Although the significance is not sufficien t to establish this beyond doubt, the high-energy gamma-ray spectrum a ppears to evolve from hard to soft as a flare progresses.