We report the observation by the Compton Gamma Ray Observatory of a spectacular flare of radio source PKS 1622 - 297 .
A peak flux of ( 17 \pm 3 ) \times 10 ^ { -6 } cm ^ { -2 } s ^ { -1 } ( E > 100 MeV ) was observed .
The corresponding isotropic luminosity is 2.9 \times 10 ^ { 49 } erg/s .
We find that PKS 1622 - 297 exhibits \gamma -ray intra-day variability .
A flux increase by a factor of at least 3.6 was observed to occur in less than 7.1 hours ( with 99 % confidence ) .
Assuming an exponential rise , the corresponding doubling time is less than 3.8 hours .
A significant flux decrease by a factor of \sim 2 in 9.7 hours was also observed .
Without beaming , the rapid flux change and large isotropic luminosity are inconsistent with the Elliot-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 implied by the observed lack of pair-production opacity ( assuming x-rays are emitted co-spatially with the \gamma -rays ) .
Simultaneous observation by EGRET and OSSE finds a spectrum adequately fit by a power law with photon index of - 1.9 .
Although the significance is not sufficient to establish this beyond doubt , the high-energy \gamma -ray spectrum appears to evolve from hard to soft as a flare progresses .