Short-Lived s-Process Gamma-Ray Lines in Type II Supernovae

Area of Science:

• Nuclear astrophysics
• Stellar evolution
• Supernova nucleosynthesis

Background:

• Helium burning in massive stars is crucial for element production.
• The s-process (slow neutron capture) is a key nucleosynthesis pathway.
• Understanding presupernova conditions informs supernova observations.

Purpose of the Study:

• To calculate nuclear abundances in helium-burning shells of presupernova stars.
• To investigate the production of specific isotopes via neutron capture reactions.
• To predict the detectability of gamma-ray emissions from supernova remnants.

Main Methods:

• Modeling nuclear abundances in stellar interiors.
• Simulating neutron production via the (22)Ne(alpha,n)(23)Mg reaction.
• Assessing the survival of synthesized isotopes through supernova shockwaves.

Main Results:

• For stars > 20 solar masses, the (22)Ne(alpha,n)(23)Mg reaction produces sufficient neutrons for s-process nucleosynthesis.
• Iron-59 (half-life 45 days) and cobalt-60 (half-life 5.3 years) are synthesized.
• These isotopes are predicted to survive supernova shocks.

Conclusions:

• Gamma rays from the decay of iron-59 and cobalt-60 should be detectable from most galactic type II supernovae.
• These specific gamma-ray lines are unlikely to be observable from supernova 1987A due to its distance and low metallicity.