Detection of the Characteristic Pion-Decay Signature in Supernova Remnants

By M. Ackermann, M. Ajello, A. Allafort, L. Baldini, J. Ballet, G. Barbiellini, M. Baring, D. Bastieri, K. Bechtol, R. Bellazzini and 159 more. Science, 2013

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Accelerated Protons Although cosmic rays were first detected a hundred years ago, their origin is still not fully understood. Comic rays are high-energy particles, mostly protons, which bombard Earth from outer space. Most of those that originate from within our galaxy are thought to be accelerated in the shock waves from the explosion of massive stars, or supernovae. Protons accelerated in a supernova remnant will collide with interstellar material producing pions, a type of subatomic particle, which will then decay into gamma rays. Ackermann et al. (p. 807) present measurements of the energy spectra of two supernova remnants in our galaxy, IC443 and W44, in the energy range below 100 MeV down to 60 MeV with the Fermi Gamma-Ray Space Telescope. The spectra reveal the pion-decay feature that is a signature of accelerated protons. The gamma-ray spectra of two supernova remnants in our Galaxy show the signature of proton acceleration. Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/4907dccc9e4baf2c0260beea6262e35829e154b7

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Citations in the corpus

Theoretical Challenges in Galaxy Formation (2016, background): “…the ’knee’ in the CR spectrum is considered to be diffusive shock acceleration (DSA, see e.g. Bell 1978, Blandford & Ostriker 1978) and non-linear DSA (Malkov & O’C Drury 2001) in shocks of supernova remnants (SNR) (see Hillas 2005, for a review, and recent observations by Ackermann et al. 2013).”
The origin of galactic cosmic rays (2013, neutral): “Figure 12 (from Ackermann et al. 2013) shows the gamma-ray spectra of SNRs IC443 (left panel) and W44 (right panel), where the pion bump is well visible.”
SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. I. ACCELERATION EFFICIENCY (2013, background): “Also, γ-rays from SNRs are often interpreted to be of hadronic origin (see, e.g., Caprioli 2011; Ackermann et al. 2013), suggesting that nuclei acceleration can be efficient at SNR forward shocks (about 10% in Tycho, see Morlino & Caprioli 2012).”
Contrastive Pessimistic Likelihood Estimation for Semi-Supervised Classification (2015, methodology): “A handful of recent examples from the applied and natural sciences can be found in some of the earlier-mentioned references: [5], [6], [8], [9], [13].”
Searches for Extended and Point-like Neutrino Sources with Four Years of IceCube Data (2014, background): “The catalog contains four SNRs associated with molecular clouds in the northern sky (Abdo et al. 2007, 2009a, 2009b, 2010; Ackermann et al. 2013; Fiasson et al. 2009) that were previously considered in Aartsen et al. (2013c), and six newly introduced sources from SNRCat in the southern sky.”
The Nine Lives of Cosmic Rays in Galaxies (2015, background): “A hadronic emission signature has at last been found in the W44 and IC443 remnants with Fermi -LAT and AGILE (Ackermann et al. 2013b, Cardillo et al. 2014), although it will not constitute firm evidence of the acceleration of CR nuclei until the measurements are extended to well below the pion peak ”
A hadronic origin for ultra-high-frequency-peaked BL Lac objects (2014, background): “…al. 2012; Murase et al. 2012) Proton-proton interactions (important in denser environments, such as supernovae remnants or micro-quasars, see e.g. Ackermann et al. 2013b; Romero et al. 2003, respectively) are commonly neglected in blazar hadronic models, because the particle density in the…”
IceCube-Gen2: the window to the extreme Universe (2020, background): “The Fermi LAT has observed features in the gamma-ray spectra of the shell-type supernova remnants IC 443 and W44 [205] that can be related to hadronic processes.”
The First LHAASO Catalog of Gamma-Ray Sources (2023, background): “Important evidence about the acceleration of GeV–TeV CRs were found in two ancient supernova remnants (Ackermann et al. 2013).”
THE FIRST FERMI LAT SUPERNOVA REMNANT CATALOG (2015, background): “However, such a parametrization does not account for deviations from a PL in the particle and photon spectra, while spectral curvature has been measured for several SNRs interacting with MCs, such as IC 443 and W44 (Ackermann et al. 2013a) whose spectra are preferentially fitted with a logP in the p”
Sensitivity of the high altitude water Cherenkov detector to sources of multi-TeV gamma rays (2013, neutral): “The Fermi data show strong transient ﬂares in the synchrotron emission from the Crab Nebula, peaking at 50 times the quiescent state, over several days.”