Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: H.E.S.S. ToO program on nearby core-collapse Supernovae: search for
  very-high energy $\gamma$-ray emission towards the SN candidate AT2019krl in
  M74   While the youngest known supernova remnants, such as Cassiopeia A, have been
proven to be able to accelerate cosmic rays only up to
$\sim$10$^{14}\,\mathrm{eV}$ at their present evolutionary stages, recent
studies have shown that particle energies larger than a few PeV
($10^{15}\,\mathrm{eV}$) could be reached during the early stages of a
core-collapse Supernova, when the high-velocity forward shock expands into the
dense circumstellar medium shaped by the stellar progenitor wind. Such
environments, in particular the type IIn SNe whose progenitors may exhibit
mass-loss rates as high as $10^{-2}M_\odot\,\mathrm{yr}^{-1}$ \cite{smith14},
could thus lead to $\gamma$-ray emission from $\pi^0$ decay in hadronic
interactions, potentially detectable with current Cherenkov telescopes at
very-high energies. Such a detection would provide direct evidence for
efficient acceleration of CR protons/nuclei in supernovae, and hence new
insights on the long-standing issue of the origin of Galactic Cosmic Rays. In
that context, the High Energy Stereoscopic System (\hess) has been carrying out
a Target of Opportunity program since 2016 to search for such an early
very-high-energy $\gamma$-ray emission towards nearby core-collapse supernovae
and supernova candidates (up to $\sim 10~\mathrm{Mpc}$), within a few weeks
after discovery. After giving an overview of this \hess\ Target of Opportunity
program, we present the results obtained from the July 2019 observations
towards the transient \at, originally classified as a type IIn supernova, which
occurred in the galaxy M74 at $\sim 9.8\,\mathrm{Mpc}$. Although its nature
still remains unclear, the derived \hess\ constraints on this transient are
placed in the general context of the expected VHE $\gamma$-ray emission from
core-collapse supernovae.

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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: econ
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an
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The categories of this paper are: math
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The categories of this paper are: mtrl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: cond-mat
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The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas