MeV Gamma Rays from Fission: A Distinct Signature of Actinide Production in Neutron Star Mergers. (arXiv:2008.03335v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wang_X/0/1/0/all/0/1">Xilu Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vassh_N/0/1/0/all/0/1">Nicole Vassh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sprouse_T/0/1/0/all/0/1">Trevor Sprouse</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mumpower_M/0/1/0/all/0/1">Matthew Mumpower</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vogt_R/0/1/0/all/0/1">Ramona Vogt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Randrup_J/0/1/0/all/0/1">Jorgen Randrup</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Surman_R/0/1/0/all/0/1">Rebecca Surman</a>
Neutron star mergers (NSMs) are the first verified site of rapid neutron
capture (r-process) nucleosynthesis, and could emit gamma rays from the
radioactive isotopes synthesized in the neutron-rich ejecta. These MeV gamma
rays may provide a unique and direct probe of the NSM environment as well
insight into the nature of the r process, just as observed gammas from the 56Ni
radioactive decay chain provide a window into supernova nucleosynthesis. In
this work, we include the photons from fission processes for the first time in
estimates of the MeV gamma-ray signal expected from a NSM event. We consider
NSM ejecta compositions with a range of neutron richness and find a dramatic
difference in the predicted signal depending on whether or not fissioning
nuclei are produced. The difference is most striking at photon energies above
~3.5 MeV and at a relatively late time, several days after the merger event,
when the ejecta is optically thin. We estimate that a Galactic NSM could be
detectable by a next generation gamma-ray detector such as AMEGO in the MeV
range, up to ~10^4 days after the merger, if fissioning nuclei are robustly
produced in the event.
Neutron star mergers (NSMs) are the first verified site of rapid neutron
capture (r-process) nucleosynthesis, and could emit gamma rays from the
radioactive isotopes synthesized in the neutron-rich ejecta. These MeV gamma
rays may provide a unique and direct probe of the NSM environment as well
insight into the nature of the r process, just as observed gammas from the 56Ni
radioactive decay chain provide a window into supernova nucleosynthesis. In
this work, we include the photons from fission processes for the first time in
estimates of the MeV gamma-ray signal expected from a NSM event. We consider
NSM ejecta compositions with a range of neutron richness and find a dramatic
difference in the predicted signal depending on whether or not fissioning
nuclei are produced. The difference is most striking at photon energies above
~3.5 MeV and at a relatively late time, several days after the merger event,
when the ejecta is optically thin. We estimate that a Galactic NSM could be
detectable by a next generation gamma-ray detector such as AMEGO in the MeV
range, up to ~10^4 days after the merger, if fissioning nuclei are robustly
produced in the event.
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