Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Emergence of a Lanthanide-Rich Kilonova Following the Merger of Two
  Neutron Stars   We report the discovery and monitoring of the near-infrared counterpart
(AT2017gfo) of a binary neutron-star merger event detected as a gravitational
wave source by Advanced LIGO/Virgo (GW170817) and as a short gamma-ray burst by
Fermi/GBM and Integral/SPI-ACS (GRB170817A). The evolution of the transient
light is consistent with predictions for the behaviour of a
"kilonova/macronova", powered by the radioactive decay of massive neutron-rich
nuclides created via r-process nucleosynthesis in the neutron-star ejecta. In
particular, evidence for this scenario is found from broad features seen in
Hubble Space Telescope infrared spectroscopy, similar to those predicted for
lanthanide dominated ejecta, and the much slower evolution in the near-infrared
Ks-band compared to the optical. This indicates that the late-time light is
dominated by high-opacity lanthanide-rich ejecta, suggesting nucleosynthesis to
the 3rd r-process peak (atomic masses A~195). This discovery confirms that
neutron-star mergers produce kilo-/macronovae and that they are at least a
major - if not the dominant - site of rapid neutron capture nucleosynthesis in
the universe.

12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
19
The categories of this paper are: eess