Neutral pion emission from accelerated protons in the supernova remnant W44

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We present the AGILE gamma-ray observations in the energy range 50MeV-10GeV 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 radi...

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Detalles Bibliográficos
Autores principales: Giuliani, A., Cardillo, M., Tavani, M., Fukui, Y., Yoshiike, S., Torii, K., Dubner, G., Castelletti, G., Barbiellini, G., Bulgarelli, A., Caraveo, P., Costa, E., Cattaneo, P.W., Chen, A., Contessi, T., Del Monte, E., Donnarumma, I., Evangelista, Y., Feroci, M., Gianotti, F., Lazzarotto, F., Lucarelli, F., Longo, F., Marisaldi, M., Mereghetti, S., Pacciani, L., Pellizzoni, A., Piano, G., Picozza, P., Pittori, C., Pucella, G., Rapisarda, M., Rappoldi, A., Sabatini, S., Soffitta, P., Striani, E., Trifoglio, M., Trois, A., Vercellone, S., Verrecchia, F., Vittorini, V., Colafrancesco, S., Giommi, P., Bignami, G.
Formato: JOUR
Materias:
acceleration of particles
cosmic rays
gamma rays: general
ISM: supernova remnants
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_20418205_v742_n2_p_Giuliani
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
Descripción
Sumario:We present the AGILE gamma-ray observations in the energy range 50MeV-10GeV 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 [SII] 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 1GeV 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 E c = 6 ± 1GeV. Direct evidence for pion emission is then established in an SNR for the first time. © 2011. The American Astronomical Society. All rights reserved..

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