A gamma-ray flare from PKS 2255-282

A gamma-ray flare from the quasar PKS 2255-282 was detected in 1997 Decembe r by the EGRET instrument on board the Compton Gamma Ray Observatory (CGRO) . Previously undetected at gamma-ray energies, the source remained bright f or 2 weeks of observations with weak evidence of gamma-ray variability with in the hare observation. The average flux was (1.6 +/- 0.3) x 10(-6) cm(-2) s(-1) above: 100 MeV with a hard power-law index of 1.7 +/- 0.3. This plac es the outburst among the brightest detected by EGRET. A later Rossi X-Ray Timing Explorer (RXTE) observation revealed a simple power-law spectrum wit h photon index 1.8 and 2-10 keV flux of 1.44 x 10(-11) ergs cm(-2) s(-1). T his paper describes the CGRO and RXTE observations and data analysis, the s ource identification, and gamma-ray variability. We also consider the broad band spectrum, albeit on the basis of nonsimultaneous multiwavelength measu rements, and the nature of the outburst from this source in the context of other known gamma-ray blazars.