RXTE observations of PKS 2155-304 during the November 1997 gamma-ray outburst

We present X-ray observations of the nearby BL Lac PKS 2155-304 taken when it was undergoing a GeV/TeV gamma-ray outburst. During the outburst we meas ured X-ray fluxes in the 2-10 keV band that are the largest ever observed f or PKS 2155-304, Comparison of these November 1997 measurements and other X -ray observations made contemporaneously with GeV or TeV gamma-ray observat ions indicate that X-ray and gamma-ray emissions are correlated. Measuremen ts with X-ray all-sky monitors such as the ASM/RXTE and MOXE can therefore signal the presence of outbursts at gamma-ray energies from PKS 2155-304. ( C) 1999 Elsevier Science B.V. All rights reserved.