A comprehensive search for gamma-ray lines in the first year of data from the INTEGRAL spectrometer

We have carried out an extensive search for gamma-ray lines in the first year of public data from the spectrometer (SPI) on the INTEGRAL mission. INTEGRAL has spent a large fraction of its observing time in the Galactic plane with particular concentration in the Galactic center (GC) region (similar to 3 Ms in the first year). Hence the most sensitive search regions are in the Galactic plane and center. The phase space of the search spans the energy range 20-8000 keV and line widths from 0 to 1000 keV (FWHM). It includes both diffuse and pointlike emission. We have searched for variable emission on timescales down to similar to 1000 s. Diffuse emission has been searched for on a range of different spatial scales from similar to 20 degrees (the approximate field of view of the spectrometer) up to the entire Galactic plane. Our search procedures were verified by the recovery of the known gamma-ray lines at 511 and 1809 keV at the appropriate intensities and significances. We find no evidence for any previously unknown gamma-ray lines. The upper limits range from a few x 10(-5) to a few x 10(-2) cm(-2) s(-1) depending on line width, energy, and exposure; regions of strong instrumental background lines were excluded from the search. Comparison is made between our results and various prior predictions of astrophysical lines.