NEUTRAL PION EMISSION FROM ACCELERATED PROTONS IN THE SUPERNOVA REMNANT W44

By A. Giuliani, M. Cardillo, M. Tavani, Y. Fukui, S. Yoshiike, K. Torii, G. Dubner, G. Castelletti, G. Barbiellini, A. Bulgarelli and 34 more. 2011

186 citations recorded by the source corpus.

We present the AGILE gamma-ray observations in the energy range 50 MeV–10 GeV of the supernova remnant (SNR) W44, one of the most interesting systems for studying cosmic-ray production. W44 is an intermediate-age SNR (∼20, 000 years) and its ejecta expand in a dense medium as shown by a prominent radio shell, nearby molecular clouds, and bright [S ii] emitting regions. We extend our gamma-ray analysis to energies substantially lower than previous measurements which could not conclusively establish the nature of the radiation. We find that gamma-ray emission matches remarkably well both the position and shape of the inner SNR shocked plasma. Furthermore, the gamma-ray spectrum shows a prominent peak near 1 GeV with a clear decrement at energies below a few hundreds of MeV as expected from neutral pion decay. Here we demonstrate that (1) hadron-dominated models are consistent with all W44 multiwavelength constraints derived from radio, optical, X-ray, and gamma-ray observations; (2) ad hoc lepton-dominated models fail to explain simultaneously the well-constrained gamma-ray and radio spectra, and require a circumstellar density much larger than the value derived from observations; and (3) the hadron energy spectrum is well described by a power law (with index s = 3.0 ± 0.1) and a low-energy cut-off at Ec = 6 ± 1 GeV. Direct evidence for pion emission is then established in an SNR for the first time.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/a688f250df732623cc4f533ac64917420ffc45ec

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. A. Strong
2. E. Orlando
3. Anna Franckowiak
4. Troy A. Porter
5. Igor V. Moskalenko
6. I. Grenier
7. A. Bykov
8. J. Vink

In Nuclear and High Energy Physics

1. A. Strong
2. E. Orlando
3. Anna Franckowiak
4. Troy A. Porter
5. I. Grenier
6. Igor V. Moskalenko
7. A. Bykov
8. J. Vink

Citations in the corpus

• The origin of galactic cosmic rays (2013, unknown): “Recently the AGILE (Giuliani et al. 2010, 2011) and Fermi-LAT (Abdo et al. 2009, 2010a, 2010b, 2010c; Ackermann et al. 2013) collaborations claimed the detection of the much sought-after pion bump in the gamma-ray spectrum.”
• Observational Signatures of Particle Acceleration in Supernova Remnants (2012, background): “However, new AGILE observations of two supernova remnants (W44, W28 Giuliani et al., 2011, 2010) reveal the characteristic low energy cut-off expected for pion decay (Figure 13).”
• THE FIRST FERMI LAT SUPERNOVA REMNANT CATALOG (2015, background): “The launches of AGILE in 2007 and Fermi in 2008 finally provided the capability to unambiguously identify SNRs in γ-rays and to detect the spectral signature of accelerated protons from the brightest of them (Giuliani et al. 2011; Ackermann et al. 2013a).”