Early-time <i>γ</i>-ray constraints on cosmic-ray acceleration in the core-collapse SN 2023ixf with the <i>Fermi</i> Large Area Telescope

<jats:p><jats:italic>Context.</jats:italic> While supernova remnants (SNRs) have been considered the most relevant Galactic cosmic ray (CR) accelerators for decades, core-collapse supernovae (CCSNe) could accelerate particles during the earliest stages of their evolution and hence contribute to the CR energy budget in the Galaxy. Some SNRs have indeed been associated with TeV <jats:italic>γ</jats:italic>-rays, yet proton acceleration efficiency during the early stages of an SN expansion remains mostly unconstrained.</jats:p> <jats:p><jats:italic>Aims.</jats:italic> The multi-wavelength observation of SN 2023ixf, a Type II supernova (SN) in the nearby galaxy M 101 (at a distance of 6.85 Mpc), opens the possibility to constrain CR acceleration within a few days after the collapse of the red super-giant stellar progenitor. With this work, we intend to provide a phenomenological, quasi-model-independent constraint on the CR acceleration efficiency during this event at photon energies above 100 MeV.</jats:p> <jats:p><jats:italic>Methods.</jats:italic> We performed a maximum-likelihood analysis of <jats:italic>γ</jats:italic>-ray data from the <jats:italic>Fermi</jats:italic> Large Area Telescope up to one month after the SN explosion. We searched for high-energy, non-thermal emission from its expanding shock, and estimated the underlying hadronic CR energy reservoir assuming a power-law proton distribution consistent with standard diffusive shock acceleration.</jats:p> <jats:p><jats:italic>Results.</jats:italic> We do not find significant <jats:italic>γ</jats:italic>-ray emission from SN 2023ixf. Nonetheless, our non-detection provides the first limit on the energy transferred to the population of hadronic CRs during the very early expansion of a CCSN.</jats:p> <jats:p><jats:italic>Conclusions.</jats:italic> Under reasonable assumptions, our limits would imply a maximum efficiency on the CR acceleration of as low as 1%, which is inconsistent with the common estimate . Authors: Martí-Devesa, G. [Univ. Innsbruck (Austria); Univ. of Trieste (Italy); SLAC] (ORCID:0000000307666473); Cheung, C. C. [Naval Research Lab. (NRL), Washington, DC (United States)] (ORCID:0000000243770174); Di Lalla, N. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics & Cosmology]; Renaud, M. [Montpellier Univ. 2 (France). Lab. Universe And Particles De Montpellier]; Principe, G. [Univ. of Trieste (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Trieste (Italy); Istituto Nazionale di Astrofisica (INAF), Bologna (Italy)]. DOE Contract: AC02-76SF00515. Subjects: 79 ASTRONOMY AND ASTROPHYSICS