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

TL;DR

This study conducted the deepest Galactic Plane survey for titanium-44 gamma-ray emission using INTEGRAL/IBIS, setting new sensitivity limits, confirming Cas A as the only significant source, and highlighting the rarity of 44Ti-producing supernova remnants.

Contribution

It provides the most sensitive survey to date for 44Ti sources in the Galaxy, improving detection limits and constraining the occurrence of such sources.

Findings

Only Cas A shows significant 44Ti emission among young SNRs.

No other sources detected at >5 sigma significance, confirming rarity.

Survey sensitivity improved by a factor of ~5 over previous missions.

Abstract

We report the results of the deepest Galactic Plane (|b| < 17.5 deg) 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 years of operation. The peak sensitivity of our survey reached an unprecedented level of $4.8\times10^{-6}$ erg s$^{-1}$ cm$^{-2}$ (3 sigma) that improves the sensitivity of the survey done by CGRO/COMPTEL by a factor of ~5. As a result, constraining upper limits for all sources from the catalog 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 5 sigma confirming previous claims of the rarity of such 44Ti-producing SNRs.