Galactic survey of 44Ti sources with the IBIS telescope onboard INTEGRAL

We report the results of the deepest Galactic plane (|b| < 17.5°) survey in the 67.9 and 78.4 keV nuclear de-excitation lines of titanium-44 (⁴⁴Ti) performed using the data acquired with the IBIS/ISGRI instrument onboard the INTEGRAL satellite during 12 yr of operation. The peak sensitivity of our survey reached an unprecedented level of 4.8 × 10^-6 ph cm^-2 s^-1 (3σ) that improves the sensitivity of the survey done by Compton Gamma-Ray Observatory/COMPTEL by a factor of ∼5. As a result, constraining upper limits for all sources from the catalogue of Galactic supernova remnants (SNRs; Green 2014) are derived. These upper limits can be used to estimate the exposure needed to detect ⁴⁴Ti emission from any known SNR using existing and prospective X- and gamma-ray telescopes. Among the youngest Galactic SNRs, only Cas A shows significant ⁴⁴Ti emission flux in good agreement with the NuSTAR measurements. We did not detect any other sources of titanium emission in the Galactic plane at significance level higher than 5σ confirming previous claims of the rarity of such ⁴⁴Ti-producing SNRs.