The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration

The middle-aged supernova remnant (SNR) W44 has recently attracted attention because of its relevance regarding the origin of Galactic cosmic-rays. For the first time for a SNR, the gamma-ray missions AGILE and Fermi have established the spectral continuum below 200 MeV, which can be attributed to a...

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Autores principales:	Cardillo, M., Tavani, M., Giuliani, A., Yoshiike, S., Sano, H., Fukuda, T., Fukui, Y., Castelletti, G., Dubner, G.
Formato:	JOUR
Materias:	Acceleration of particles Astroparticle physics Gamma rays: ISM ISM: supernova remnants Radiation mechanisms: non-thermal Shock waves Industry Particle accelerators Stars Ultraviolet spectroscopy Gamma rays: isms Radiation mechanisms: nonthermal Gamma rays
Acceso en línea:	http://hdl.handle.net/20.500.12110/paper_00046361_v565_n_p_Cardillo
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

id	todo:paper_00046361_v565_n_p_Cardillo
record_format	dspace
spelling	todo:paper_00046361_v565_n_p_Cardillo2023-10-03T14:00:49Z The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration Cardillo, M. Tavani, M. Giuliani, A. Yoshiike, S. Sano, H. Fukuda, T. Fukui, Y. Castelletti, G. Dubner, G. Acceleration of particles Astroparticle physics Gamma rays: ISM ISM: supernova remnants Radiation mechanisms: non-thermal Shock waves Industry Particle accelerators Shock waves Stars Ultraviolet spectroscopy Acceleration of particles Astroparticle physics Gamma rays: isms ISM: supernova remnants Radiation mechanisms: nonthermal Gamma rays The middle-aged supernova remnant (SNR) W44 has recently attracted attention because of its relevance regarding the origin of Galactic cosmic-rays. For the first time for a SNR, the gamma-ray missions AGILE and Fermi have established the spectral continuum below 200 MeV, which can be attributed to a neutral pion emission. Confirming the hadronic origin of the gamma-ray emission near 100 MeV is then of the greatest importance. Our paper is focused on a global re-assessment of all available data and models of particle acceleration in W44 with the goal of determining the hadronic and leptonic contributions to the overall spectrum on a firm ground. We also present new gamma-ray and CO NANTEN2 data on W44 and compare them to recently published AGILE and Fermi data. Our analysis strengthens previous studies and observations of the W44 complex environment and provides new information for more detailed modeling. In particular, we determine that the average gas density of the regions emitting 100 MeV-10 GeV gamma-rays is relatively high (n ~ 250-300 cm-3). The hadronic interpretation of the gamma-ray spectrum of W44 is viable and supported by strong evidence. It implies a relatively large value for the average magnetic field (B ≥ 102 μG) in the SNR surroundings, which is a sign of field amplification by shock-driven turbulence. Our new analysis establishes that the spectral index of the proton energy distribution function is p1 = 2.2 ± 0.1 at low energies and p2 = 3.2 ± 0.1 at high energies. We critically discuss hadronic versus leptonic-only models of emission taking radio and gamma-ray data into account simultaneously. We find that the leptonic models are disfavored by the combination of radio and gamma-ray data. Having determined the hadronic nature of the gamma-ray emission on firm ground, a number of theoretical challenges remain to be addressed. © ESO 2014. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_00046361_v565_n_p_Cardillo
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	Acceleration of particles Astroparticle physics Gamma rays: ISM ISM: supernova remnants Radiation mechanisms: non-thermal Shock waves Industry Particle accelerators Shock waves Stars Ultraviolet spectroscopy Acceleration of particles Astroparticle physics Gamma rays: isms ISM: supernova remnants Radiation mechanisms: nonthermal Gamma rays
spellingShingle	Acceleration of particles Astroparticle physics Gamma rays: ISM ISM: supernova remnants Radiation mechanisms: non-thermal Shock waves Industry Particle accelerators Shock waves Stars Ultraviolet spectroscopy Acceleration of particles Astroparticle physics Gamma rays: isms ISM: supernova remnants Radiation mechanisms: nonthermal Gamma rays Cardillo, M. Tavani, M. Giuliani, A. Yoshiike, S. Sano, H. Fukuda, T. Fukui, Y. Castelletti, G. Dubner, G. The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration
topic_facet	Acceleration of particles Astroparticle physics Gamma rays: ISM ISM: supernova remnants Radiation mechanisms: non-thermal Shock waves Industry Particle accelerators Shock waves Stars Ultraviolet spectroscopy Acceleration of particles Astroparticle physics Gamma rays: isms ISM: supernova remnants Radiation mechanisms: nonthermal Gamma rays
description	The middle-aged supernova remnant (SNR) W44 has recently attracted attention because of its relevance regarding the origin of Galactic cosmic-rays. For the first time for a SNR, the gamma-ray missions AGILE and Fermi have established the spectral continuum below 200 MeV, which can be attributed to a neutral pion emission. Confirming the hadronic origin of the gamma-ray emission near 100 MeV is then of the greatest importance. Our paper is focused on a global re-assessment of all available data and models of particle acceleration in W44 with the goal of determining the hadronic and leptonic contributions to the overall spectrum on a firm ground. We also present new gamma-ray and CO NANTEN2 data on W44 and compare them to recently published AGILE and Fermi data. Our analysis strengthens previous studies and observations of the W44 complex environment and provides new information for more detailed modeling. In particular, we determine that the average gas density of the regions emitting 100 MeV-10 GeV gamma-rays is relatively high (n ~ 250-300 cm-3). The hadronic interpretation of the gamma-ray spectrum of W44 is viable and supported by strong evidence. It implies a relatively large value for the average magnetic field (B ≥ 102 μG) in the SNR surroundings, which is a sign of field amplification by shock-driven turbulence. Our new analysis establishes that the spectral index of the proton energy distribution function is p1 = 2.2 ± 0.1 at low energies and p2 = 3.2 ± 0.1 at high energies. We critically discuss hadronic versus leptonic-only models of emission taking radio and gamma-ray data into account simultaneously. We find that the leptonic models are disfavored by the combination of radio and gamma-ray data. Having determined the hadronic nature of the gamma-ray emission on firm ground, a number of theoretical challenges remain to be addressed. © ESO 2014.
format	JOUR
author	Cardillo, M. Tavani, M. Giuliani, A. Yoshiike, S. Sano, H. Fukuda, T. Fukui, Y. Castelletti, G. Dubner, G.
author_facet	Cardillo, M. Tavani, M. Giuliani, A. Yoshiike, S. Sano, H. Fukuda, T. Fukui, Y. Castelletti, G. Dubner, G.
author_sort	Cardillo, M.
title	The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration
title_short	The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration
title_full	The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration
title_fullStr	The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration
title_full_unstemmed	The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration
title_sort	supernova remnant w44: confirmations and challenges for cosmic-ray acceleration
url	http://hdl.handle.net/20.500.12110/paper_00046361_v565_n_p_Cardillo
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The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration

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