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Gamma-Ray Emission Produced by r-process Elements from Neutron Star Mergers
Abstract The observation of a radioactively powered kilonova AT 2017gfo associated with the gravitational wave event GW170817 from a binary neutron star merger proves that these events are ideal sites for the production of heavy r -process elements. The gamma-ray photons produced by the radioactive...
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Published in: | The Astrophysical journal 2021-09, Vol.919 (1), p.59 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Abstract
The observation of a radioactively powered kilonova AT 2017gfo associated with the gravitational wave event GW170817 from a binary neutron star merger proves that these events are ideal sites for the production of heavy
r
-process elements. The gamma-ray photons produced by the radioactive decay of heavy elements are unique probes for the detailed nuclide compositions. Based on the detailed
r
-process nucleosynthesis calculations and considering radiative transport calculations for the gamma rays in different shells, we study the gamma-ray emission in a merger ejecta on a timescale of a few days. It is found that the total gamma-ray energy generation rate evolution is roughly depicted as
E
̇
∝
t
−
1.3
. For the dynamical ejecta with a low electron fraction (
Y
e
≲ 0.20), the dominant contributors of gamma-ray energy are the nuclides around the second
r
-process peak (
A
∼ 130) and the decay chain of
132
Te (
t
1/2
= 3.21 days) →
132
I (
t
1/2
= 0.10 days) →
132
Xe produces gamma-ray lines at 228, 668, and 773 keV. For the case of a wind ejecta with
Y
e
≳ 0.30, the dominant contributors of gamma-ray energy are the nuclides around the first
r
-process peak (
A
∼ 80) and the decay chain of
72
Zn (
t
1/2
= 1.93 days) →
72
Ga (
t
1/2
= 0.59 days) →
72
Ge produces gamma-ray lines at 145, 834, 2202, and 2508 keV. The peak fluxes of these lines are 10
−9
∼ 10
−7
ph cm
−2
s
−1
, which are marginally detectable with the next-generation MeV gamma-ray detector
ETCC
if the source is at a distance of 40 Mpc. |
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ISSN: | 0004-637X 1538-4357 |
DOI: | 10.3847/1538-4357/ac1267 |