An Intense Gamma‐Ray Flare of PKS 1622−297

We report the observation by the Compton Gamma Ray Observatory of aspectacular flare of radio source PKS 1622-297. A peak flux of 17E-6 cm^-2 s^-1(E > 100 MeV) was observed. The corresponding isotropic luminosity is 2.9E49erg/s. We find that PKS 1622-297 exhibits gamma-ray intra-day variability. Aflux increase by a factor of at least 3.6 was observed to occur in less than7.1 hours (with 99% confidence). Assuming an exponential rise, thecorresponding doubling time is less than 3.8 hours. A significant flux decreaseby a factor of ~2 in 9.7 hours was also observed. Without beaming, the rapidflux change and large isotropic luminosity are inconsistent with theElliot-Shapiro condition (assuming that gas accretion is the immediate sourceof power for the gamma-rays). This inconsistency suggests that the gamma-rayemission is beamed. A minimum Doppler factor of 8.1 is implied by the observedlack of pair-production opacity (assuming x-rays are emitted co-spatially withthe gamma-rays). Simultaneous observation by EGRET and OSSE finds a spectrumadequately fit by a power law with photon index of -1.9. Although thesignificance is not sufficient to establish this beyond doubt, the high-energygamma-ray spectrum appears to evolve from hard to soft as a flare progresses.Comment: 14 pages, 4 figures, 1 tabl