2013ApJ...775...52D

We revise the assumptions of the parameters involved in predicting the number of supernova remnants detectable in the nuclear lines of the decay chain of ⁴⁴Ti. Specifically, we consider the distribution of the supernova progenitors, the supernova rate in the Galaxy, the ratios of supernova types, the Galactic production of ⁴⁴Ti, and the ⁴⁴Ti yield from supernovae of different types to derive credible bounds on the expected number of detectable remnants. We find that, within 1σ uncertainty, the Galaxy should contain an average of 5.1_–2.0^+2.4 remnants detectable to a survey with a ⁴⁴Ti decay line flux limit of 10^–5 photons/cm2/s, with a probability of detecting a single remnant of 2.7_–2.4^+10.0%, and an expected number of detections between two and nine remnants, making the single detection of Cas A unlikely but consistent with our models. Our results show that the probability of detecting the brightest ⁴⁴Ti flux source at the high absolute Galactic longitude of Cas A or above is ∼10%. Using the detected flux of Cas A, we attempt to constrain the Galactic supernova rate and Galactic production of ⁴⁴Ti, but find the detection to be only weakly informative. We conclude that even future surveys having 200 times more sensitivity than state-of-the-art surveys can be guaranteed to detect only a few new remnants, with an expected number of detections between 8 and 21 at a limiting ⁴⁴Ti decay flux of 10^–7 photons/cm2/s.