SMM OBSERVATIONS OF GAMMA-RAY TRANSIENTS .2. A SEARCH FOR GAMMA-RAY LINES BETWEEN 400 AND 600 KEV FROM THE CRAB-NEBULA

We have searched spectra obtained by the Solar Maximum Mission Gamma-R ay Spectrometer during 1981-1988 for evidence of transient gamma-ray l ines from the Crab Nebula which have been reported by previous experim ents at energies 400-460 keV and 539 keV. We find no evidence for sign ificant emission in any of these lines on time scales between similar to 1 day and similar to 1 yr. Our 3 a upper limits on the transient fl ux during 1 d intervals are similar or equal to 2.2x10(-3) photons cm( -2) s(-1) for narrow lines at any energy, and similar or equal to 2.9x 10(-3) photons cm(-2) s(-1) for the 539 keV line if it is as broad as 42 keV FWHM. We also searched our data during the similar to 5 hr peri od on 1981 June 6 during which Owens, Myers, and Thompson (1985) repor ted a strong line at 405 keV. We detected no line down to a 3 sigma up per limit of 3.3x10(-3) photons cm(-2) s(-1), in disagreement with the flux 7.2+/-2.1x10(-3) photons cm(-2) s(-1) measured by Owens et al.