Crab Nebula

R. Sunyaev, E. Churazov, M. Gilfanov, A. Claret, J. Ballet, J. P. Dezalay and P. Mandrou, on behalf of the GRANAT team (IKI, Moscow; CEA, Saclay; CESR, Toulouse), report: "Evidence for an emission feature at about 545 keV in the spectrum of the Crab Nebula was found with GRANAT/SIGMA on Mar. 10-11. The peak on the image was at 5.1 sigma, and the flux in the 490-580-keV energy band corresponded to 4.5 x 10**-3 photon s-1 cm-2. The x-ray spectrum below 200 keV was consistent with that observed by SIGMA in 1990-1991. The 3-sigma upper limit on the average flux in the 490-580-keV band during the 1990-1991 observations was 1.2 x 10**-3 photon s-1 cm-2. Searches for any unusual behavior of the source (such as a wisp or glitch) at other wavelengths are urged."