Limits on the Number of Galactic Young Supernova Remnants Emitting in the Decay Lines of 44Ti

TL;DR

This study estimates the number of detectable galactic supernova remnants emitting in 44Ti decay lines, considering various astrophysical parameters, and predicts limited detection prospects even with future highly sensitive surveys.

Contribution

The paper provides updated bounds on the expected number of detectable 44Ti-emitting supernova remnants by revising key astrophysical assumptions and parameters.

Findings

Expected detectable remnants: 2 to 9

Probability of detecting Cas A: ~10%

Future surveys may detect 8 to 21 remnants

Abstract

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 1 sigma uncertainty, the Galaxy should contain an average of 5.1+2.4-2.0 remnants detectable to a survey with a 44Ti decay line flux limit of 10E-5 photons/cm2/s, with a probability of detecting a single remnant of (2.7+10.0-2.4)%, and an expected number of detections between 2 and 9 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 10E-7 photons/cm2/s.